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Title 40 CFR Part 191
Subparts B and C
Compliance Recertification
Application
for the
Waste Isolation Pilot Plant

Appendix SCR-2009
Feature, Event, and Process Screening for PA

United States Department of Energy
Waste Isolation Pilot Plant

Carlsbad Field Office
Carlsbad, New Mexico

 


Appendix SCR-2009
Feature, Event, and Process Screening for PA

 


Table of Contents

  SCR-1.0  Introduction

  SCR-2.0  Basis for FEPs Screening Process

      SCR-2.1  Requirement for FEPs

      SCR-2.2  FEPs List Development for the CCA

      SCR-2.3 Criteria for Screening of FEPs and Categorization of Retained FEPs

          SCR-2.3.1  Regulation (SO-R)

          SCR-2.3.2   Probability of Occurrence of a FEP Leading to Significant Release of Radionuclides (SO-P)

          SCR-2.3.3  Potential Consequences Associated with the Occurrence of the FEPs (SO-C)

          SCR-2.3.4  UP FEPs

          SCR-2.3.5  DP FEPs

      SCR-2.4  FEPs Categories and Timeframes

          SCR-2.4.1  Description of Natural FEPs

          SCR-2.4.2  Description of Human-Induced EPs

              SCR-2.4.2.1  Scope of Future Human Activities in PA

                  SCR-2.4.2.1.1  Criteria Concerning Future Mining

                  SCR-2.4.2.1.2  Criteria Concerning Future Drilling

                  SCR-2.4.2.1.3  Screening of Future Human EPs

          SCR-2.4.3  Description of Waste- and Repository-Induced FEPs

  SCR-3.0  FEPs

  SCR-4.0  Screening of Natural FEPs

      SCR-4.1  Geological FEPs

          SCR-4.1.1  Stratigraphy

              SCR-4.1.1.1   FEP Numbers:    N1 and N2 FEP Titles:        Stratigraphy(N1)                           Brine Reservoir (N2)

              SCR-4.1.1.2  Screening Decision: UP (N1)                               DP (N2)

                  SCR-4.1.1.2.1  Summary of New Information

                  SCR-4.1.1.2.2  Screening Argument

          SCR-4.1.2  Tectonics

              SCR-4.1.2.1    FEP Numbers:   N3, N4, and N5 FEP Titles:        Changes in Regional Stress (N3)                            Regional Tectonics (N4)                            Regional Uplift and Subsidence (N5)

                  SCR-4.1.2.1.1  Screening Decision:  SO-C

                  SCR-4.1.2.1.2  Summary of New Information

                  SCR-4.1.2.1.3  Screening Argument

                  SCR-4.1.2.1.4  Tectonic Setting and Site Structural Features

                  SCR-4.1.2.1.5  Tectonics

          SCR-4.1.3  Structural FEPs

              SCR-4.1.3.1  Deformation

                  SCR-4.1.3.1.1    FEP Numbers: N6 and N7 FEP Titles:              Salt Deformation (N6)                                              Diapirism (N7)

                      SCR-4.1.3.1.1.1  Screening Decision:  SO-P

                      SCR-4.1.3.1.1.2  Summary of New Information

                      SCR-4.1.3.1.1.3  Screening Argument

              SCR-4.1.3.2  Fracture Development

                  SCR-4.1.3.2.1    FEP Number:    N8 FEP Title:         Formation of Fractures

                      SCR-4.1.3.2.1.1  Screening Decision: SO-P, UP (Repository)

                      SCR-4.1.3.2.1.2  Summary of New Information

                      SCR-4.1.3.2.1.3  Screening Argument

                  SCR-4.1.3.2.2    FEP Number:    N9 FEP Title:               Changes in Fracture Properties

                      SCR-4.1.3.2.2.1  Screening Decision:  SO-C, UP (near repository)

                      SCR-4.1.3.2.2.2  Summary of New Information

                      SCR-4.1.3.2.2.3  Screening Argument

                  SCR-4.1.3.2.3    FEP Numbers:       N10 and N11 FEP Titles:            Formation of New Faults (N10)                                Fault Movement (N11)

                      SCR-4.1.3.2.3.1  Screening Decision:  SO-P

                      SCR-4.1.3.2.3.2  Summary of New Information

                      SCR-4.1.3.2.3.3  Screening Argument

                  SCR-4.1.3.2.4    FEP Number:    N12 FEP Title:               Seismic Activity

                      SCR-4.1.3.2.4.1  Screening Decision:  UP

                      SCR-4.1.3.2.4.2  Summary of New Information

                      SCR-4.1.3.2.4.3  Screening Argument

                        SCR-4.1.3.2.4.4Causes of Seismic Activity

                      SCR-4.1.3.2.4.5  Groundshaking

                      SCR-4.1.3.2.4.6  Seismic Risk in the Region of the WIPP

          SCR-4.1.4  Crustal Process

              SCR-4.1.4.1    FEP Number:    N13 FEP Title:          Volcanic Activity

                  SCR-4.1.4.1.1  Screening Decision:  SO-P

                  SCR-4.1.4.1.2  Summary of New Information

                  SCR-4.1.4.1.3  Screening Argument

              SCR-4.1.4.2    FEP Number:    N14 FEP Title:          Magmatic Activity

          :          :SCR-4.1.4.2.1Screening Decision:  SO-C

                  SCR-4.1.4.2.2  Summary of New Information

                  SCR-4.1.4.2.3  Screening Argument

                  SCR-4.1.4.2.4    FEP Number:    N15 FEP Title:         Metamorphic Activity

                      SCR-4.1.4.2.4.1  Screening Decision:  SO-P

                      SCR-4.1.4.2.4.2  Summary of New Information

                      SCR-4.1.4.2.4.3  Screening Argument

          SCR-4.1.5  Geochemical Processes

              SCR-4.1.5.1    FEP Number:    N16 FEP Title:          Shallow Dissolution (including lateral dissolution)

                  SCR-4.1.5.1.1  Screening Decision:  UP

                  SCR-4.1.5.1.2  Summary of New Information

                  SCR-4.1.5.1.3  Screening Argument

                  SCR-4.1.5.1.4  Shallow Dissolution

              SCR-4.1.5.2    FEP Numbers:   N18, N20, and N21 FEP Titles:        Deep Dissolution (N18)                           Breccia Pipes (N20)                           Collapse Breccias (N21)

                  SCR-4.1.5.2.1  Screening Decision:  SO-P

                  SCR-4.1.5.2.2  Summary of New Information

                  SCR-4.1.5.2.3Screening Argument

                  SCR-4.1.5.2.4  Deep Dissolution

                  SCR-4.1.5.2.5  Dissolution within the Castile and Lower Salado

                  SCR-4.1.5.2.6  Collapse Breccias at Basin Margins

                  SCR-4.1.5.2.7  Summary of Deep Dissolution

              SCR-4.1.5.3   FEP Number:     N22 FEP Title:          Fracture Infill

                  SCR-4.1.5.3.1  Screening Decision:  SO-C – Beneficial

                  SCR-4.1.5.3.2  Summary of New Information

                  SCR-4.1.5.3.3  Screening Argument

                      SCR-4.1.5.3.3.1  Mineralization

      SCR-4.2Subsurface Hydrological FEPs

          SCR-4.2.1  Groundwater Characteristics

              SCR-4.2.1.1    FEP Numbers:   N23, N24, N25, and N27 FEP Titles:        Saturated Groundwater Flow (N23)                           Unsaturated Groundwater Flow (N24)                           Fracture Flow (N25)                           Effects of Preferential Pathways (N27)

                  SCR-4.2.1.1.1  Screening Decision:  UP

                  SCR-4.2.1.1.2  Summary of New Information

                  SCR-4.2.1.1.3  Screening Argument

              SCR-4.2.1.2    FEP Number:    N26 FEP Title:          Density Effect on Groundwater Flow

                  SCR-4.2.1.2.1  Screening Decision:  SO-C

                  SCR-4.2.1.2.2  Summary of New Information

                  SCR-4.2.1.2.3  Screening Argument

          SCR-4.2.2  Changes in Groundwater Flow

              SCR-4.2.2.1    FEP Number:    N28 FEP Title:          Thermal Effects on Groundwater Flow

                  SCR-4.2.2.1.1  Screening Decision:  SO-C

                  SCR-4.2.2.1.2  Summary of New Information

                  SCR-4.2.2.1.3  Screening Argument

              SCR-4.2.2.2    FEP Number:    N29 FEP Title:          Saline Intrusion (hydrogeological effects)

                  SCR-4.2.2.2.1  Screening Decision:  SO-P

                  SCR-4.2.2.2.2  Summary of New Information

                  SCR-4.2.2.2.3  Screening Argument

              SCR-4.2.2.3    FEP Number:    N30 FEP Title:          Freshwater Intrusion (hydrogeological effects)

                  SCR-4.2.2.3.1  Screening Decision:  SO-P

                  SCR-4.2.2.3.2  Summary

                      SCR-4.2.2.3.2.1  Screening Argument

              SCR-4.2.2.4    FEP Number:    N31 FEP Title:          Hydrological Response to Earthquakes

                  SCR-4.2.2.4.1  Screening Decision:  SO-C

                  SCR-4.2.2.4.2  Summary of New Information

                  SCR-4.2.2.4.3  Screening Argument

                      SCR-4.2.2.4.3.1  Hydrological Effects of Seismic Activity

              SCR-4.2.2.5    FEP Number:    N32 FEP Title:          Natural Gas Intrusion

                  SCR-4.2.2.5.1  Screening decision:  SO-P

                  SCR-4.2.2.5.2  Summary of New Information

                      SCR-4.2.2.5.2.1  Screening Argument

      SCR-4.3  Subsurface Geochemical FEPs

          SCR-4.3.1  Groundwater Geochemistry

              SCR-4.3.1.1    FEP Number:    N33 FEP Title:          Groundwater Geochemistry

                  SCR-4.3.1.1.1  Screening Decision:  UP

                  SCR-4.3.1.1.2  Summary of New Information

                  SCR-4.3.1.1.3  Screening Argument

              SCR-4.3.1.2    FEP Numbers: N34 and N38 FEP Titles:       Saline Intrusion (geochemical effects) (N34)                          Effects of Dissolution (N38)

                  SCR-4.3.1.2.1  Screening Decision:  SO-C

                  SCR-4.3.1.2.2  Summary of New Information

                  SCR-4.3.1.2.3  Screening Argument

              SCR-4.3.1.3    FEP Numbers: N35, N36, and N37 FEP Titles:       Freshwater Intrusion (Geochemical Effects) (N35)                          Change in Groundwater Eh (N36)                          Changes in Groundwater pH (N37)

                  SCR-4.3.1.3.1  Screening Decision:  SO-C

                  SCR-4.3.1.3.2  Summary of New Information

                  SCR-4.3.1.3.3  Screening Argument

      SCR-4.4  Geomorphological FEPs

          SCR-4.4.1  Physiography

              SCR-4.4.1.1    FEP Number:    N39 FEP Title:          Physiography

                  SCR-4.4.1.1.1  Screening Decision:  UP

                  SCR-4.4.1.1.2Summary of New Information

                  SCR-4.4.1.1.3  Screening Argument

              SCR-4.4.1.2    FEP Number:   N40 FEP Title:        Impact of a Large Meteorite

                  SCR-4.4.1.2.1  Screening Decision:  SO-P

              SCR-4.4.1.3  Summary of New Information

              SCR-4.4.1.4  Screening Argument

              SCR-4.4.1.5    FEP Number: N41 and N42 FEP Titles:      Mechanical Weathering (N41)                         Chemical Weathering (N42)

                  SCR-4.4.1.5.1  Screening Decision:  SO-C

                  SCR-4.4.1.5.2  Summary of New Information

                  SCR-4.4.1.5.3  Screening Argument

              SCR-4.4.1.6    FEP Numbers: N43, N44, and N45 FEP Titles:       Aeolian Erosion (N43)                          Fluvial Erosion (N44)                          Mass Wasting (N45)

                  SCR-4.4.1.6.1  Screening Decision:  SO-C

                  SCR-4.4.1.6.2  Summary of New Information

                  SCR-4.4.1.6.3  Screening Argument

              SCR-4.4.1.7    FEP Number:   N50 FEP Title:        Soil Development

                  SCR-4.4.1.7.1  Screening Decision:  SO-C

                  SCR-4.4.1.7.2  Summary of New Information

                  SCR-4.4.1.7.3  Screening Argument

      SCR-4.5  Surface Hydrological FEPs

          SCR-4.5.1  Depositional Processes

              SCR-4.5.1.1    FEP Numbers: N46, N47, N48, and N49 FEP Titles:       Aeolian Deposition (N46)                          Fluvial Deposition (47)                          Lacustrine Deposition (N48)                          Mass Waste (Deposition) (N49)

                  SCR-4.5.1.1.1  Screening Decision:  SO-C

                  SCR-4.5.1.1.2  Summary of New Information

                  SCR-4.5.1.1.3  Screening Argument

          SCR-4.5.2  Streams and Lakes

              SCR-4.5.2.1    FEPs Number: N51 FEPs Title:       Stream and River Flow

                  SCR-4.5.2.1.1  Screening Decision:  SO-C

                  SCR-4.5.2.1.2  Summary of New Information

                  SCR-4.5.2.1.3  Screening Argument

              SCR-4.5.2.2    FEP Number:   N52 FEP Title:        Surface Water Bodies

                  SCR-4.5.2.2.1  Screening Decision:  SO-C

                  SCR-4.5.2.2.2  Summary of New Information

                  SCR-4.5.2.2.3  Screening Argument

          SCR-4.5.3  Groundwater Recharge and Discharge

              SCR-4.5.3.1    FEP Numbers:   N53, N54, and N55 FEP Titles:        Groundwater Discharge (N53)                           Groundwater Recharge (N54)                           Infiltration (N55)

                  SCR-4.5.3.1.1  Screening Decision:  UP

                  SCR-4.5.3.1.2  Summary of New Information

                  SCR-4.5.3.1.3  Screening Argument

              SCR-4.5.3.2    FEP Number:    N56 FEP Title:          Changes in Groundwater Recharge and Discharge

                  SCR-4.5.3.2.1  Screening Decision:  UP

                  SCR-4.5.3.2.2  Summary of New Information

                  SCR-4.5.3.2.3  Screening Argument

              SCR-4.5.3.3    FEP Numbers: N57 and N58 FEP Titles:       Lake Formation (N57)                          River Flooding (N58)

                  SCR-4.5.3.3.1  Screening Decision:  SO-C

                  SCR-4.5.3.3.2  Summary of New Information

                  SCR-4.5.3.3.3  Screening Argument

      SCR-4.6  Climate EPs

          SCR-4.6.1  Climate and Climate Changes

              SCR-4.6.1.1    FEP Numbers: N59 and N60 FEP Titles:       Precipitation (N59)                          Temperature (N60)

                  SCR-4.6.1.1.1  Screening Decision:  UP

                  SCR-4.6.1.1.2  Summary of New Information

                  SCR-4.6.1.1.3  Screening Argument

              SCR-4.6.1.2    FEP Number:   N61 FEP Title:        Climate Change

                  SCR-4.6.1.2.1  Screening Decision:  UP

                  SCR-4.6.1.2.2  Summary of New Information

                  SCR-4.6.1.2.3  Screening Argument

              SCR-4.6.1.3    FEP Numbers:   N62 and N63 FEP Titles:        Glaciation (N62)                           Permafrost (N63)

                  SCR-4.6.1.3.1  Screening Decision:  SO-P

                  SCR-4.6.1.3.2  Summary of New Information

                  SCR-4.6.1.3.3  Screening Argument

      SCR-4.7  Marine FEPs

          SCR-4.7.1  Seas, Sedimentation, and Level Changes

              SCR-4.7.1.1    FEP Numbers:   N64 and N65 FEP Titles:        Seas and Oceans (N64)                           Estuaries (N65)

                  SCR-4.7.1.1.1  Screening Decision:  SO-C

                  SCR-4.7.1.1.2  Summary of New Information

                  SCR-4.7.1.1.3  Screening Argument

              SCR-4.7.1.2    FEPs Numbers: N66 and N67 FEPs Titles:     Coastal Erosion (N66)                          Marine Sediment Transport and Deposition (N67)

                  SCR-4.7.1.2.1  Screening Decision:  SO-C

                  SCR-4.7.1.2.2  Summary of New Information

                  SCR-4.7.1.2.3  Screening Argument

              SCR-4.7.1.3    FEP Number:   N68 FEP Title:        Sea Level Changes

                  SCR-4.7.1.3.1  Screening Decision:  SO-C

                  SCR-4.7.1.3.2  Summary of New Information

                  SCR-4.7.1.3.3  Screening Argument

      SCR-4.8  Ecological FEPs

          SCR-4.8.1  Flora and Fauna

              SCR-4.8.1.1    FEP Numbers: N69 and N70 FEP Titles:       Plants (N69)                          Animals (N70)

                  SCR-4.8.1.1.1  Screening Decision:  SO-C

                  SCR-4.8.1.1.2  Summary of New Information

                  SCR-4.8.1.1.3  Screening Argument

              SCR-4.8.1.2    FEP Number:   N71 FEP Title:        Microbes

                  SCR-4.8.1.2.1  Screening Decision:     SO-C  UP for colloidal effects and gas generation

                  SCR-4.8.1.2.2  Summary of New Information

                  SCR-4.8.1.2.3  Screening Argument

              SCR-4.8.1.3    FEP Number:   N72 FEP Title:        Natural Ecological Development

                  SCR-4.8.1.3.1  Screening Decision:  SO-C

                  SCR-4.8.1.3.2  Summary of New Information

                  SCR-4.8.1.3.3  Screening Argument

   SCR-5.0  Screening of Human-Induced EPs

      SCR-5.1  Human-Induced Geological EPs

          SCR-5.1.1  Drilling

              SCR-5.1.1.1    FEP Numbers:   H1, H2, H4, H8, and H9 FEP Titles:       Oil and Gas Exploration (H1)                          Potash Exploration (H2)                          Oil and Gas Exploitation (H4)                          Other Resources (drilling for) (H8)                          Enhanced Oil and Gas Recovery (drilling for) (H9)

                  SCR-5.1.1.1.1    Screening Decision:   SO-C (HCN)                                     DP (Future)

                  SCR-5.1.1.1.2  Summary of New Information

                  SCR-5.1.1.1.3  Historical, Current, and Near-Future Human EPs

                  SCR-5.1.1.1.4  Future Human EPs

              SCR-5.1.1.2    FEP Numbers:   H3 and H5 FEP Titles:       Water Resources Exploration (H3)                          Groundwater Exploitation (H5)

                  SCR-5.1.1.2.1    Screening Decision:    SO-C (HCN)                                      SO-C (Future)

                  SCR-5.1.1.2.2  Summary of New Information

                  SCR-5.1.1.2.3  Screening Argument

                  SCR-5.1.1.2.4  Historical, Current, and Near-Future Human EPs

                  SCR-5.1.1.2.5  Future Human EPs

              SCR-5.1.1.3    FEP Numbers:   H6, H7, H10, H11, and H12 FEP Titles:       Archeological Investigations (H6)                          Geothermal Energy Production (H7)                          Liquid Waste Disposal (H10)                          Hydrocarbon Storage (H11)                          Deliberate Drilling Intrusion (H12)

                  SCR-5.1.1.3.1    Screening Decision:    SO-R (HCN)                                      SO-R (Future)

                  SCR-5.1.1.3.2  Summary of New Information

                  SCR-5.1.1.3.3  Screening Argument

                      SCR-5.1.1.3.3.1  Historic, Current, and Near-Future EPs

                  SCR-5.1.1.3.4  Future Human EPs

          SCR-5.1.2  Excavation Activities

              SCR-5.1.2.1    FEP Number:   H13 FEP Title:        Conventional Underground Potash Mining

                  SCR-5.1.2.1.1    Screening Decision:   UP (HCN)                                     DP (Future)

                  SCR-5.1.2.1.2  Summary of New Information

                  SCR-5.1.2.1.3  Screening Argument

              SCR-5.1.2.2    FEP Number:   H14 FEP Title:        Other Resources (mining for)

                  SCR-5.1.2.2.1    Screening Decision:    SO-C (HCN)                                      SO-R (Future)

                  SCR-5.1.2.2.2  Summary of New Information

                  SCR-5.1.2.2.3  Screening Argument

              SCR-5.1.2.3    FEP Numbers:   H15 and H16 FEP Titles:       Tunneling (H15)                          Construction of Underground Facilities (H16)

                  SCR-5.1.2.3.1    Screening Decision:      SO-R (HCN)                                        SO-R (Future)

                  SCR-5.1.2.3.2  Summary

                  SCR-5.1.2.3.3  Screening Argument

              SCR-5.1.2.4    FEP Number:   H17 FEP Title:        Archeological Excavations

                  SCR-5.1.2.4.1    Screening Decision:   SO-C (HCN)                                     SO-R (Future)

                  SCR-5.1.2.4.2  Summary of New Information

                  SCR-5.1.2.4.3  Screening Argument

              SCR-5.1.2.5    FEP Number:   H18 FEP Title:        Deliberate Mining Intrusion

                  SCR-5.1.2.5.1    Screening Decision:      SO-R (HCN)                                        SO-R (Future)

                  SCR-5.1.2.5.2  Summary of New Information

                  SCR-5.1.2.5.3  Screening Argument

          SCR-5.1.3  Subsurface Explosions

              SCR-5.1.3.1    FEPs Number:   H19 FEP Title:        Explosions for Resource Recovery

                  SCR-5.1.3.1.1    Screening Decision:    SO-C (HCN)                                      SO-R (Future)

                  SCR-5.1.3.1.2  Summary of New Information

                  SCR-5.1.3.1.3  Screening Argument

                  SCR-5.1.3.1.4  Historical, Current, and Near-Future Human EPs

              SCR-5.1.3.2    FEPs Number:   H20 FEP Title:        Underground Nuclear Device Testing

                  SCR-5.1.3.2.1    Screening Decision:    SO-C (HCN)                                      SO-R (Future)

                  SCR-5.1.3.2.2  Summary of New Information

                  SCR-5.1.3.2.3  Screening Argument

                      SCR-5.1.3.2.3.1  Historical, Current, and Near-Future Human EPs

                      SCR-5.1.3.2.3.2  Future Human EPs

      SCR-5.2  Subsurface Hydrological and Geochemical EPs

          SCR-5.2.1  Borehole Fluid Flow

              SCR-5.2.1.1    FEP Number:   H21 FEP Title:        Drilling Fluid Flow

                  SCR-5.2.1.1.1    Screening Decision:   SO-C (HCN)                                     DP (Future)

                  SCR-5.2.1.1.2  Summary of New Information

                  SCR-5.2.1.1.3  Screening Argument

                      SCR-5.2.1.1.3.1  Historical, Current, and Near-Future Human EPs

                      SCR-5.2.1.1.3.2  Future Human EPs

              SCR-5.2.1.2    FEP Number:   H22 FEP Title:        Drilling Fluid Loss

                  SCR-5.2.1.2.1    Screening Decision:   SO-C (HCN)                                     DP (Future)

                  SCR-5.2.1.2.2  Summary of New Information

                  SCR-5.2.1.2.3Screening Argument

                      SCR-5.2.1.2.3.1  Historical, Current, and Near-Future Human EPs

                      SCR-5.2.1.2.3.2  Future Human EPs

              SCR-5.2.1.3    FEP Number:   H23 FEP Title:        Blowouts

                  SCR-5.2.1.3.1    Screening Decision:   SO-C (HCN)                                     DP (Future)

                  SCR-5.2.1.3.2  Summary of New Information

                  SCR-5.2.1.3.3  Screening Argument

                      SCR-5.2.1.3.3.1  Historical, Current, and Near-Future Human EPs

                      SCR-5.2.1.3.3.2  Future Human EPs—Boreholes that Intersect the Waste Disposal Region

                      SCR-5.2.1.3.3.3  Hydraulic Effects of Drilling-Induced Flow

              SCR-5.2.1.4    FEP Number:   H24 FEP Title:        Drilling-Induced Geochemical Changes

                  SCR-5.2.1.4.1    Screening Decision:   UP (HCN)                                     DP (Future)

                  SCR-5.2.1.4.2  Summary of New Information

                  SCR-5.2.1.4.3  Screening Argument

                      SCR-5.2.1.4.3.1  Historical, Current, and Near-Future Human EPs

                      SCR-5.2.1.4.3.2  Geochemical Effects of Drilling-Induced Flow–HCN

                      SCR-5.2.1.4.3.3  Future Human EPs — Boreholes that Intersect the Waste Disposal Region

                      SCR-5.2.1.4.3.4  Geochemical Effects of Drilling-Induced Flow-Future

                       SCR-5.2.1.4.3.5    Future Human EPs — Boreholes That Do Not Intersect the Waste Disposal Region

                      SCR-5.2.1.4.3.6  Geochemical Effects of Drilling-Induced Flow

              SCR-5.2.1.5    FEP Numbers: H25 and H26 FEP Titles:       Oil and Gas Extraction                          Groundwater Extraction

                  SCR-5.2.1.5.1    Screening Decision:   SO-C (HCN)                                     SO-R (Future)

                  SCR-5.2.1.5.2  Summary of New Information

                      SCR-5.2.1.5.2.1  Screening Argument

                      SCR-5.2.1.5.2.2  Historical, Current, and Near-Future Human EPs

                      SCR-5.2.1.5.2.3  Future Human EPs

              SCR-5.2.1.6    FEP Numbers: H27, H28, and H29 FEP Titles:       Liquid Waste Disposal – OB (H27)                          Enhanced Oil and Gas Production – OB (H28)                          Hydrocarbon Storage – OB (H29)

                  SCR-5.2.1.6.1    Screening Decision:    SO-C (HCN)                                      SO-C (Future)

                  SCR-5.2.1.6.2  Summary of New Information

                  SCR-5.2.1.6.3  Screening Argument

                      SCR-5.2.1.6.3.1  Historical, Current, and Near-Future Human EPs

                      SCR-5.2.1.6.3.2  Hydraulic Effects of Leakage through Injection Boreholes

                       SCR-5.2.1.6.3.3  Effects of Density Changes Resulting from Leakage Through Injection Boreholes

                      SCR-5.2.1.6.3.4  Geochemical Effects of Leakage through Injection Boreholes

                      SCR-5.2.1.6.3.5  Future Human EPs

              SCR-5.2.1.7    FEP Numbers: H60, H61, and H62 FEP Titles:       Liquid Waste Disposal – IB (H60)                          Enhanced Oil and Gas Production – IB (H61)                          Hydrocarbon Storage – IB (H62)

                  SCR-5.2.1.7.1    Screening Decision:   SO-R (HCN)                                     SO-R (Future)

                  SCR-5.2.1.7.2  Summary of New Information

                  SCR-5.2.1.7.3  Screening Argument

                      SCR-5.2.1.7.3.1  Historical, Current, and Near-Future Human EPs

                      SCR-5.2.1.7.3.2  Future Human EPs

              SCR-5.2.1.8    FEP Number:   H30 FEP Title:        Fluid Injection-Induced Geochemical Changes

                  SCR-5.2.1.8.1    Screening Decision:   UP (HCN)                                     SO-R (Future)

                  SCR-5.2.1.8.2  Summary of New Information

                  SCR-5.2.1.8.3  Screening Argument

                      SCR-5.2.1.8.3.1  Geochemical Effects of Leakage through Injection Boreholes

                      SCR-5.2.1.8.3.2  Future Human EPs

              SCR-5.2.1.9    FEP Number:   H31 FEP Title:        Natural Borehole Fluid Flow (H31)

                  SCR-5.2.1.9.1    Screening Decision:   SO-C (HCN)                                     SO-C (Future, holes not penetrating waste panels)                                     DP (Future, holes through waste panels)

                  SCR-5.2.1.9.2  Summary of New Information

                  SCR-5.2.1.9.3  Screening Argument

                      SCR-5.2.1.9.3.1  Historical, Current, and Near-Future Human EPs

                      SCR-5.2.1.9.3.2  Hydraulic Effects of Flow through Abandoned Boreholes

                      SCR-5.2.1.9.3.3  Connections Between the Culebra and Deeper Units

                      SCR-5.2.1.9.3.4  Connections Between the Culebra and Shallower Units

                       SCR-5.2.1.9.3.5    Changes in Fluid Density Resulting from Flow Through Abandoned Boreholes

                      SCR-5.2.1.9.3.6  Future Human EPs

                      SCR-5.2.1.9.3.7  Hydraulic Effects of Flow Through Abandoned Boreholes

                      SCR-5.2.1.9.3.8  Fluid Flow and Radionuclide Transport in the Culebra

                       SCR-5.2.1.9.3.9    Changes in Fluid Density Resulting from Flow Through Abandoned Boreholes

                SCR-5.2.1.10  FEP Number:   H32 FEP Title:        Waste-Induced Borehole Flow

                    SCR-5.2.1.10.1  Screening Decision:   SO-R (HCN)                                     DP (Future)

                    SCR-5.2.1.10.2  Summary of New Information

                    SCR-5.2.1.10.3  Screening Argument

                        SCR-5.2.1.10.3.1  Future Human EPs

                         SCR-5.2.1.10.3.2  Hydraulic Effects of Flow Through Abandoned Boreholes

                SCR-5.2.1.11   FEP Number:   H34 FEP Title:        Borehole-Induced Solution and Subsidence

                    SCR-5.2.1.11.1  Screening Decision:   SO-C (HCN)                                     SO-C (Future)

                    SCR-5.2.1.11.2  Summary of New Information

                    SCR-5.2.1.11.3  Screening Argument

                        SCR-5.2.1.11.3.1  Historical, Current, and Near-Future Human EPs

                        SCR-5.2.1.11.3.2  Future Human EPs

                SCR-5.2.1.12  FEP Number:   H35 FEP Title:        Borehole-Induced Mineralization

                    SCR-5.2.1.12.1  Screening Decision:   SO-C (HCN)                                     SO-C (Future)

                    SCR-5.2.1.12.2  Summary of New Information

                    SCR-5.2.1.12.3Screening Argument

                        SCR-5.2.1.12.3.1  Borehole-Induced Mineralization

                    SCR-5.2.1.12.4  Future Human EPs

                         SCR-5.2.1.12.4.1  Borehole-Induced Mineralization

                SCR-5.2.1.13   FEP Number:   H36 FEP Title:        Borehole-Induced Geochemical Changes

                    SCR-5.2.1.13.1  Screening Decision:   UP (HCN)                                     DP (Future)                                     SO-C for units other than the Culebra

                    SCR-5.2.1.13.2  Summary of New Information

                    SCR-5.2.1.13.3  Screening Argument

                         SCR-5.2.1.13.3.1  Geochemical Effects of Borehole Flow

                    SCR-5.2.1.13.4  Future Human EPs

                         SCR-5.2.1.13.4.1  Geochemical Effects of Flow Through Abandoned Boreholes

          SCR-5.2.2  Excavation-Induced Flow

              SCR-5.2.2.1    FEP Number:   H37 FEP Title:        Changes in Groundwater Flow Due to Mining

                  SCR-5.2.2.1.1    Screening Decision:   UP (HCN)                                     DP (Future)

                  SCR-5.2.2.1.2  Summary of New Information

                  SCR-5.2.2.1.3  Screening Argument

                      SCR-5.2.2.1.3.1  Historical, Current, and Near-Future Human EPs

                      SCR-5.2.2.1.3.2  Hydrogeological Effects of Mining

                  SCR-5.2.2.1.4  Future Human EPs

              SCR-5.2.2.2    FEP Number:   H38 FEP Title:        Changes in Geochemistry Due to Mining

                  SCR-5.2.2.2.1    Screening Decision:   SO-C (HCN)                                     SO-R (Future)

                  SCR-5.2.2.2.2 Summary of New Information

                  SCR-5.2.2.2.3  Screening Argument

                      SCR-5.2.2.2.3.1  Historical, Current, and Near-Future Human EPs

                      SCR-5.2.2.2.3.2  Geochemical Effects of Mining

                      SCR-5.2.2.2.3.3  Future Human EPs

              SCR-5.2.2.3    FEP Number    H58 FEP Title:        Solution Mining for Potash

                  SCR-5.2.2.3.1    Screening Decision:   SO-R (HCN)                                     SO-R (Future)

                  SCR-5.2.2.3.2  Summary of New Information

                  SCR-5.2.2.3.3  Screening Argument

              SCR-5.2.2.4    FEP Number:   H59 FEP Title:        Solution Mining for Other Resources

                  SCR-5.2.2.4.1    Screening Decision:    SO-C (HCN)                                      SO-C (Future)

                  SCR-5.2.2.4.2  Summary of New Information

                  SCR-5.2.2.4.3  Screening Argument

                  SCR-5.2.2.4.4  Solution Mining for Brine

                      SCR-5.2.2.4.4.1  Current Brine Wells within the Delaware Basin

                  SCR-5.2.2.4.5  Solution Mining for Other Minerals

                  SCR-5.2.2.4.6  Solution Mining for Gas Storage

                  SCR-5.2.2.4.7  Solution Mining for Disposal

                  SCR-5.2.2.4.8  Effects of Solution Mining

                      SCR-5.2.2.4.8.1  Subsidence

                      SCR-5.2.2.4.8.2  Hydrogeological Effects

                      SCR-5.2.2.4.8.3  Geochemical Effects

                  SCR-5.2.2.4.9  Conclusion of Low Consequence

          SCR-5.2.3  Explosion-Induced Flow

              SCR-5.2.3.1    FEP Number:   H39 FEPs Title:       Changes in Groundwater Flow Due to Explosions

                  SCR-5.2.3.1.1    Screening Decision:    SO-C (HCN)                                      SO-R (Future)

                  SCR-5.2.3.1.2 Summary of New Information

                  SCR-5.2.3.1.3  Screening Argument

                      SCR-5.2.3.1.3.1  Historical, Current, and Near-Future Human EPs

                      SCR-5.2.3.1.3.2  Future Human EPs

      SCR-5.3  Geomorphological EPS

          SCR-5.3.1  Land Use Changes

              SCR-5.3.1.1    FEP Number:   H40 FEP Title:        Land Use Changes

                  SCR-5.3.1.1.1    Screening Decision:    SO-R (HCN)                                      SO-R (Future)

                  SCR-5.3.1.1.2  Summary of New Information

                  SCR-5.3.1.1.3  Screening Argument

                  SCR-5.3.1.1.4  Historical, Current, and Near-Future Human EPs

                  SCR-5.3.1.1.5  Future Human EPs

              SCR-5.3.1.2    FEP Number:   H41 FEP Title:        Surface Disruptions

                  SCR-5.3.1.2.1    Screening Decision:   UP (HCN)                                     SO-C (Future)

                  SCR-5.3.1.2.2  Summary of New Information

                  SCR-5.3.1.2.3  Screening Argument

                  SCR-5.3.1.2.4  Historical, Current, and Near-Future Human EPs

                  SCR-5.3.1.2.5  Future Human EPs

      SCR-5.4  Surface Hydrological EPs

          SCR-5.4.1  Water Control and Use

              SCR-5.4.1.1    FEP Numbers: H42, H43, and H44 FEP Titles:       Damming of Streams and Rivers (H42)                          Reservoirs (H43)                          Irrigation (H44)

                  SCR-5.4.1.1.1    Screening Decision:   SO-C (HCN)                                     SO-R (Future)

                  SCR-5.4.1.1.2  Summary of New Information

                  SCR-5.4.1.1.3  Screening Argument

                  SCR-5.4.1.1.4  Historical, Current, and Near-Future Human EPs

                  SCR-5.4.1.1.5  Future Human EPs

              SCR-5.4.1.2    FEP Number:   H45 FEP Title:        Lake Usage

                  SCR-5.4.1.2.1    Screening Decision:    SO-R (HCN)                                      SO-R (Future)

                  SCR-5.4.1.2.2  Summary of New Information

                  SCR-5.4.1.2.3  Screening Argument

                  SCR-5.4.1.2.4  Historical, Current, and Near-Future Human EPs

                  SCR-5.4.1.2.5  Future Human EPs

              SCR-5.4.1.3    FEP Number:   H46 FEP Title:        Altered Soil or Surface Water Chemistry by Human Activities

                  SCR-5.4.1.3.1    Screening Decision:   SO-C (HCN)                                     SO-R (Future)

                  SCR-5.4.1.3.2  Summary of New Information

                  SCR-5.4.1.3.3  Screening Argument

                  SCR-5.4.1.3.4  Historical, Current, and Near-Future Human EPs

                  SCR-5.4.1.3.5  Future Human EPs

      SCR-5.5  Climatic EPs

          SCR-5.5.1  Anthropogenic Climate Change

              SCR-5.5.1.1    FEP Numbers: H47, H48, and H49

                  SCR-5.5.1.1.1    Screening Decision:   SO-R (HCN)                                     SO-R (Future)

                  SCR-5.5.1.1.2  Summary of New Information

                  SCR-5.5.1.1.3  Anthropogenic Climate Change

      SCR-5.6  Marine EPs

          SCR-5.6.1  Marine Activities

              SCR-5.6.1.1    FEP Numbers: H50, H51, and H52 FEP Titles:       Costal Water Use (H50)                          Seawater Use (H51)                          Estuarine Water Use (H52)

                  SCR-5.6.1.1.1    Screening Decision:   SO-R (HCN)                                     SO-R (Future)

                  SCR-5.6.1.1.2  Summary of New Information

                  SCR-5.6.1.1.3  Screening Argument

                  SCR-5.6.1.1.4  Historical, Current, and Near-Future Human EPs

                  SCR-5.6.1.1.5  Future Human EPs

      SCR-5.7  Ecological EPs

          SCR-5.7.1  Agricultural Activities

              SCR-5.7.1.1    FEP Numbers: H53, H54, and H55 FEP Titles:       Arable Farming (H53)                          Ranching (H54)                          Fish Farming (H55)

                  SCR-5.7.1.1.1    Screening Decision:    SO-C (HCN) (H53, H54)                                      SO-R (HCN) (H55)                                      SO-R (Future) (H53, H54, H55)

                  SCR-5.7.1.1.2  Summary of New Information

                  SCR-5.7.1.1.3  Screening Argument

                  SCR-5.7.1.1.4  Historical, Current, and Near-Future Human EPs

                  SCR-5.7.1.1.5  Future Human EPs

          SCR-5.7.2  Social and Technological Development

              SCR-5.7.2.1    FEP Number:   H56 FEP Title:        Demographic Change and Urban Development

                  SCR-5.7.2.1.1    Screening Decision:    SO-R (HCN)                                      SO-R (Future)

                  SCR-5.7.2.1.2  Summary of New Information

                  SCR-5.7.2.1.3  Screening Argument

              SCR-5.7.2.2    FEP Number:   H57 FEP Title:        Loss of Records

                  SCR-5.7.2.2.1    Screening Decision:   Not Applicable (N/A) (HCN)                                     DP (Future)

                  SCR-5.7.2.2.2  Summary of New Information

                  SCR-5.7.2.2.3Screening Argument

   SCR-6.0  Waste and Repository-Induced FEPs

      SCR-6.1  Waste and Repository Characteristics

          SCR-6.1.1  Repository Characteristics

              SCR-6.1.1.1    FEP Number:    W1 FEP Title:          Disposal Geometry

                  SCR-6.1.1.1.1  Screening Decision:  UP

                  SCR-6.1.1.1.2  Summary of New Information

              SCR-6.1.1.2  Screening Argument

          SCR-6.1.2  Waste Characteristics

              SCR-6.1.2.1    FEP Number:    W2 and W3 FEP Title:          Waste Inventory                           Heterogeneity of Waste Forms

                  SCR-6.1.2.1.1    Screening Decision:   UP (W2)                                     DP (W3)

                  SCR-6.1.2.1.2  Summary of New Information

                  SCR-6.1.2.1.3  Screening Argument

          SCR-6.1.3  Container Characteristics

              SCR-6.1.3.1    FEP Number:    W4 FEP Title:          Container Form

                  SCR-6.1.3.1.1  Screening Decision:  SO-C – Beneficial

                  SCR-6.1.3.1.2  Summary of New Information

                  SCR-6.1.3.1.3  Screening Argument

              SCR-6.1.3.2    FEP Number:    W5 FEP Title:          Container Material Inventory

                  SCR-6.1.3.2.1  Screening Decision:  UP

                  SCR-6.1.3.2.2  Summary of New Information

                  SCR-6.1.3.2.3  Screening Argument

          SCR-6.1.4  Seal Characteristics

              SCR-6.1.4.1    FEP Numbers:   W6, W7, W109, and W110 FEP Titles:        Shaft Seal Geometry (W6)                           Shaft Seal Physical Properties (W7)                           Panel Closure Geometry (W109)                           Panel Closure Physical Properties (W110)

                  SCR-6.1.4.1.1  Screening Decision:  UP

                  SCR-6.1.4.1.2  Summary of New Information

                  SCR-6.1.4.1.3  Screening Argument

              SCR-6.1.4.2    FEP Numbers:   W8, W111 FEP Titles:        Shaft Seal Chemical Composition (W8)                           Panel Closure Chemical Composition (W111)

                  SCR-6.1.4.2.1  Screening Decision:  SO-C Beneficial

                  SCR-6.1.4.2.2  Summary of New Information

                  SCR-6.1.4.2.3  Screening Argument

                  SCR-6.1.4.2.4  Repository Seals (Shaft and Panel Closures)

          SCR-6.1.5  Backfill Characteristics

              SCR-6.1.5.1    FEP Number:    W9 FEP Title:          Backfill Physical Properties

                  SCR-6.1.5.1.1  Screening Decision:  SO-C

                  SCR-6.1.5.1.2  Summary of New Information

                  SCR-6.1.5.1.3  Screening Argument

              SCR-6.1.5.2    FEP Number:    W10 FEP Title:          Backfill Chemical Composition

                  SCR-6.1.5.2.1  Screening Decision:  UP

                  SCR-6.1.5.2.2  Summary of New Information

                  SCR-6.1.5.2.3  Screening Argument

          SCR-6.1.6  Post-Closure Monitoring Characteristics

              SCR-6.1.6.1    FEPs Number:   W11 FEP Title:          Post-Closure Monitoring

                  SCR-6.1.6.1.1  Screening Decision:  SO-C

                  SCR-6.1.6.1.2  Summary of New Information

                  SCR-6.1.6.1.3  Screening Argument

      SCR-6.2  Radiological FEPs

          SCR-6.2.1  Radioactive Decay and Heat

              SCR-6.2.1.1    FEP Number:    W12 FEP Title:          Radionuclide Decay and Ingrowth

                  SCR-6.2.1.1.1  Screening Decision:  UP

                  SCR-6.2.1.1.2  Summary of New Information

                  SCR-6.2.1.1.3  Screening Argument

              SCR-6.2.1.2    FEP Number:    W13 FEP Title:          Heat From Radioactive Decay

                  SCR-6.2.1.2.1  Screening Decision:  SO-C

                  SCR-6.2.1.2.2  Summary of New Information

              SCR-6.2.1.3  Screening Argument

              SCR-6.2.1.4    FEPs Number:   W14 FEPs Title:        Nuclear Criticality: Heat

                  SCR-6.2.1.4.1  Screening Decision:  SO-P

                  SCR-6.2.1.4.2  Summary of New Information

                  SCR-6.2.1.4.3  Screening Argument

          SCR-6.2.2  Radiological Effects on Material Properties

              SCR-6.2.2.1    FEP Numbers:   W15, W16, W17, and W112 FEP Titles:        Radiological Effects on Waste(W15)                           Radiological Effects on Containers (W16)                           Radiological Effects on Shaft Seals (W17)                           Radiological Effects on Panel Closures (W112)

                  SCR-6.2.2.1.1  Screening Decision:  SO-C

                  SCR-6.2.2.1.2  Summary of New Information

                  SCR-6.2.2.1.3  Screening Argument

      SCR-6.3  Geological and Mechanical FEPs

          SCR-6.3.1  Excavation-Induced Changes

              SCR-6.3.1.1    FEP Numbers:   W18 and W19 FEP Titles:        Disturbed Rock Zone (W18)                           Excavation-Induced Change in Stress (W19)

                  SCR-6.3.1.1.1  Screening Decision:  UP

                  SCR-6.3.1.1.2  Summary of New Information

                  SCR-6.3.1.1.3  Screening Argument

              SCR-6.3.1.2    FEP Numbers:   W20 and W21 FEP Titles:        Salt Creep(W20)                           Change in the Stress Field (W21)

                  SCR-6.3.1.2.1  Screening Decision:  UP

                  SCR-6.3.1.2.2  Summary of New Information

                  SCR-6.3.1.2.3  Screening Argument

              SCR-6.3.1.3    FEP Number:    W22 FEP Title:          Roof Falls

                  SCR-6.3.1.3.1  Screening Decision:  UP

                  SCR-6.3.1.3.2  Summary of New Information

                  SCR-6.3.1.3.3  Screening Argument

              SCR-6.3.1.4    FEP Numbers:   W23 and W24 FEP Titles:        Subsidence (W23)                           Large Scale Rock Fracturing (W24)

                  SCR-6.3.1.4.1    Screening Decision(s):   SO-C (W23)                                         SO-P (W24)

                  SCR-6.3.1.4.2  Summary of New Information

                  SCR-6.3.1.4.3  Screening Argument

          SCR-6.3.2  Effects of Fluid Pressure Changes

              SCR-6.3.2.1    FEP Numbers:   W25 and W26 FEP Titles:        Disruption Due to Gas Effects (W25)                           Pressurization (W26)

                  SCR-6.3.2.1.1  Screening Decision:  UP

                  SCR-6.3.2.1.2  Summary of New Information

                  SCR-6.3.2.1.3  Screening Argument

          SCR-6.3.3  Effects of Explosions

              SCR-6.3.3.1    FEP Number:    W27 FEP Title:          Gas Explosions

                  SCR-6.3.3.1.1  Screening Decision:  UP

                  SCR-6.3.3.1.2  Summary of New Information

                  SCR-6.3.3.1.3  Screening Argument

              SCR-6.3.3.2    FEP Number:    W28 FEP Title:          Nuclear Explosions

                  SCR-6.3.3.2.1  Screening Decision:  SO-P

                  SCR-6.3.3.2.2  Summary of New Information

                  SCR-6.3.3.2.3  Screening Argument

          SCR-6.3.4  Thermal Effects

              SCR-6.3.4.1    FEP Numbers:   W29, W30, W31, W72, and W73 FEP Titles:        Thermal Effects on Material Properties (W29)                           Thermally-Induced Stress Changes (W30)                           Differing Thermal Expansion of Repository Components (W31)                           Exothermic Reactions (W72)                           Concrete Hydration (W73)

                   SCR-6.3.4.1.1  Screening Decision:  SO-C

                  SCR-6.3.4.1.2  Summary of New Information

                  SCR-6.3.4.1.3  Screening Argument

          SCR-6.3.5  Mechanical Effects on Material Properties

              SCR-6.3.5.1    FEP Numbers:   W32, W36, W37, W39, W113, and W114 FEP Titles:        Consolidation of Waste (W32)                           Consolidation of Shaft Seals (W36)                           Mechanical Degradation of Shaft Seals (W37)                           Underground Boreholes (W39)                           Consolidation of Panel Closures (W113)                           Mechanical Degradation of Panel Closures (W114)

                  SCR-6.3.5.1.1  Screening Decision:  UP

                  SCR-6.3.5.1.2  Summary of New Information

                  SCR-6.3.5.1.3  Screening Argument

              SCR-6.3.5.2    FEP Number:    W33 FEP Title:          Movement of Containers

                  SCR-6.3.5.2.1  Screening Decision:  SO-C

                  SCR-6.3.5.2.2  Summary of New Information

                  SCR-6.3.5.2.3Screening Argument

              SCR-6.3.5.3    FEP Number:    W34 FEP Title:          Container Integrity

                  SCR-6.3.5.3.1  Screening Decision:  SO-C Beneficial

                  SCR-6.3.5.3.2  Summary of New Information

                  SCR-6.3.5.3.3  Screening Argument

              SCR-6.3.5.4    FEP Number:    W35 FEP Title:          Mechanical Effects of Backfill

                  SCR-6.3.5.4.1  Screening Decision:  SO-C

                  SCR-6.3.5.4.2  Summary of New Information

                  SCR-6.3.5.4.3  Screening Argument

      SCR-6.4  Subsurface Hydrological and Fluid Dynamic FEPs

          SCR-6.4.1  Repository-Induced Flow

              SCR-6.4.1.1    FEP Numbers:   W40 and W41 FEP Titles:        Brine Inflow (W40)                           Wicking (W41)

                  SCR-6.4.1.1.1  Screening Decision:  UP

                  SCR-6.4.1.1.2  Summary of New Information

                  SCR-6.4.1.1.3  Screening Argument

          SCR-6.4.2  Effects of Gas Generation

              SCR-6.4.2.1    FEP Number:    W42 FEP Title:          Fluid Flow Due to Gas Production

                  SCR-6.4.2.1.1  Screening Decision:  UP

                  SCR-6.4.2.1.2  Summary of New Information

                  SCR-6.4.2.1.3  Screening Argument

          SCR-6.4.3  Thermal Effects

              SCR-6.4.3.1    FEP Number:    W43 FEP Title:          Convection

                  SCR-6.4.3.1.1  Screening Decision:  SO-C

                  SCR-6.4.3.1.2  Summary of New Information

                  SCR-6.4.3.1.3  Screening Argument

      SCR-6.5  Geochemical and Chemical FEPs

          SCR-6.5.1  Gas Generation

              SCR-6.5.1.1    FEP Numbers:   W44, W45, and W48 FEP Titles:        Degradation of Organic Material (W44)                           Effects of Temperature on Microbial Gas Generation (W45)                           Effects of Biofilms on Microbial Gas Generation (W48)

                  SCR-6.5.1.1.1  Screening Decision:  UP

                  SCR-6.5.1.1.2  Summary of New Information

                  SCR-6.5.1.1.3  Screening Argument

                      SCR-6.5.1.1.3.1  Effects of Temperature on Microbial Gas Generation

                      SCR-6.5.1.1.3.2  Effects of Biofilms on Microbial Gas Generation

              SCR-6.5.1.2    FEP Number:    W46 FEP Title:          Effects of Pressure on Microbial Gas Generation

                  SCR-6.5.1.2.1  Screening Decision:  SO-C

                  SCR-6.5.1.2.2  Summary of New Information

                  SCR-6.5.1.2.3  Screening Argument

              SCR-6.5.1.3    FEP Number:    W47 FEP Title:          Effects of Radiation on Microbial Gas Generation

                  SCR-6.5.1.3.1  Screening Decision:  SO-C

                  SCR-6.5.1.3.2  Summary of New Information

                  SCR-6.5.1.3.3  Screening Argument

              SCR-6.5.1.4    FEP Numbers:   W49 and W51 FEP Titles:        Gasses from Metal Corrosion                           Chemical Effects of Corrosion

                  SCR-6.5.1.4.1  Screening Decision:  UP

                  SCR-6.5.1.4.2  Summary of New Information

                  SCR-6.5.1.4.3  Screening Argument

              SCR-6.5.1.5    FEP Number:    W50 FEP Title:          Galvanic Coupling (within the repository)

                  SCR-6.5.1.5.1  Screening Decision:  SO-C

                  SCR-6.5.1.5.2  Summary of New Information

                  SCR-6.5.1.5.3  Screening Argument

              SCR-6.5.1.6    FEP Number:    W52 FEP Title:          Radiolysis of Brine

                  SCR-6.5.1.6.1  Screening Decision:  SO-C

                  SCR-6.5.1.6.2Summary of New Information

                  SCR-6.5.1.6.3  Screening Argument

              SCR-6.5.1.7    FEP Number:    W53 FEP Title:          Radiolysis of Cellulose

                  SCR-6.5.1.7.1  Screening Decision:  SO-C

                  SCR-6.5.1.7.2  Summary of New Information

                  SCR-6.5.1.7.3  Screening Argument

              SCR-6.5.1.8    FEP Number:    W54 FEP Title:          Helium Gas Production

                  SCR-6.5.1.8.1  Screening Decision:  SO-C

                  SCR-6.5.1.8.2  Summary of New Information

                  SCR-6.5.1.8.3  Screening Argument

              SCR-6.5.1.9    FEP Number:    W55 FEP Title:          Radioactive Gases

                  SCR-6.5.1.9.1  Screening Decision:  SO-C

                  SCR-6.5.1.9.2  Summary of New Information

                  SCR-6.5.1.9.3  Screening Argument

          SCR-6.5.2  Speciation

              SCR-6.5.2.1    FEP Number:    W56 FEP Title:          Speciation

                  SCR-6.5.2.1.1    Screening Decision:   UP – Disposal Room                                     UP – Culebra                                     SO-C – Beneficial – Shaft Seals

                  SCR-6.5.2.1.2  Summary of New Information

                  SCR-6.5.2.1.3  Screening Argument

                      SCR-6.5.2.1.3.1  Disposal Room

                      SCR-6.5.2.1.3.2  Repository Seals

                      SCR-6.5.2.1.3.3  Culebra

              SCR-6.5.2.2    FEP Number:    W57 FEP Title:          Kinetics of Speciation

                  SCR-6.5.2.2.1  Screening Decision:  SO-C

                  SCR-6.5.2.2.2  Summary of New Information

                  SCR-6.5.2.2.3  Screening Argument

                  SCR-6.5.2.2.4  Disposal Room Equilibrium Conditions

                  SCR-6.5.2.2.5  Kinetics of Complex Formation

          SCR-6.5.3  Precipitation and Dissolution

              SCR-6.5.3.1    FEP Numbers:   W58, W59, and W60 FEP Titles:        Dissolution of Waste (W58)                           Precipitation of Secondary Minerals (W59)                           Kinetics of Precipitation and Dissolution (W60)

                  SCR-6.5.3.1.1    Screening Decision:   UP – W58                                     SO-C Beneficial – W59                                     SO-C – W60

                  SCR-6.5.3.1.2  Summary of New Information

                  SCR-6.5.3.1.3  Screening Argument

                      SCR-6.5.3.1.3.1  Disposal Room

                      SCR-6.5.3.1.3.2  Geological Units

          SCR-6.5.4  Sorption

              SCR-6.5.4.1    FEP Numbers:   W61, W62, and W63 FEP Titles:        Actinide Sorption (W61)                           Kinetics of Sorption (W62)                           Changes in Sorptive Surfaces (W63)

                  SCR-6.5.4.1.1    Screening Decision:   UP – (W61, W62) In the Culebra and Dewey Lake                                     SO-C – Beneficial – (W61, W62) In the Disposal                                     Room, Shaft Seals, Panel Closures, Other Geologic                                     Units                                     UP – (W63)

                  SCR-6.5.4.1.2  Summary of New Information

                  SCR-6.5.4.1.3  Screening Argument

                      SCR-6.5.4.1.3.1  Disposal Room

                  SCR-6.5.4.1.4  Shaft Seals and Panel Closures

                      SCR-6.5.4.1.4.1  Culebra

                      SCR-6.5.4.1.4.2  Other Geological Units

                      SCR-6.5.4.1.4.3  Sorption on Colloids, Microbes, and Particulate Material

          SCR-6.5.5  Reduction-Oxidation Chemistry

              SCR-6.5.5.1    FEP Numbers:   W64 and W66 FEP Titles:        Effects of Metal Corrosion                           Reduction-Oxidation Kinetics

                  SCR-6.5.5.1.1  Screening Decision:  UP

                  SCR-6.5.5.1.2  Summary of New Information

                  SCR-6.5.5.1.3  Screening Argument

                      SCR-6.5.5.1.3.1  Reduction-Oxidation Kinetics

                      SCR-6.5.5.1.3.2  Corrosion

              SCR-6.5.5.2    FEP Number:    W65 FEP Title:          Reduction-Oxidation Fronts

                  SCR-6.5.5.2.1  Screening Decision:  SO-P

                  SCR-6.5.5.2.2  Summary of New Information

                  SCR-6.5.5.2.3  Screening Argument

              SCR-6.5.5.3    FEP Number:    W67 FEP Title:          Localized Reducing Zones

                  SCR-6.5.5.3.1  Screening Decision:  SO-C

                  SCR-6.5.5.3.2  Summary of New Information

                  SCR-6.5.5.3.3  Screening Argument

          SCR-6.5.6  Organic Complexation

                SCR-6.5.6.11  FEP Numbers:   W68, W69, and W71 FEP Titles:        Organic Complexation (W68)                           Organic Ligands (W69)                           Kinetics of Organic Complexation (W71)

                  SCR-6.5.6.1.1    Screening Decision:    UP       – W68 and W69                                      SO-C   – W71

                  SCR-6.5.6.1.2  Summary of New Information

                  SCR-6.5.6.1.3  Screening Argument

              SCR-6.5.6.2    FEP Number:    W70 FEP Title:          Humic and Fulvic Acids

                  SCR-6.5.6.2.1  Screening Decision:  UP

                  SCR-6.5.6.2.2  Summary of New Information

                  SCR-6.5.6.2.3  Screening Argument

          SCR-6.5.7  Chemical Effects on Material Properties

              SCR-6.5.7.1    FEP Numbers:   W74, W76, and W115 FEP Titles:        Chemical Degradation of Shaft Seals (W74)                           Microbial Growth on Concrete (W76)                           Chemical Degradation of Panel Closures (W115)

                  SCR-6.5.7.1.1  Screening Decision:  UP

                  SCR-6.5.7.1.2  Summary of New Information

                  SCR-6.5.7.1.3  Screening Argument

              SCR-6.5.7.2    FEP Number:    W75 FEP Title:          Chemical Degradation of Backfill

                  SCR-6.5.7.2.1  Screening Decision:  SO-C

                  SCR-6.5.7.2.2  Summary of New Information

                  SCR-6.5.7.2.3  Screening Argument

      SCR-6.6  Contaminant Transport Mode FEPs

          SCR-6.6.1  Solute and Colloid Transport

              SCR-6.6.1.1    FEP Number:    W77 FEP Title:          Solute Transport

                  SCR-6.6.1.1.1  Screening Decision:  UP

                  SCR-6.6.1.1.2  Summary of New Information

                  SCR-6.6.1.1.3  Screening Argument

              SCR-6.6.1.2    FEP Numbers:   W78, W79, W80, and W81 FEP Titles:        Colloidal Transport (W78)                           Colloidal Formation and Stability (W79)                           Colloidal Filtration (W80)                           Colloidal Sorption (W81)

                  SCR-6.6.1.2.1  Screening Decision:  UP

                  SCR-6.6.1.2.2  Summary of New Information

                  SCR-6.6.1.2.3  Screening Argument

          SCR-6.6.2  Particle Transport

              SCR-6.6.2.1    FEP Numbers:   W82, W83, W84, W85, and W86 FEP Titles:        Suspension of Particles (W82)                           Rinse (W83)                           Cuttings (W84)                           Cavings (W85)                           Spallings (W86)

                  SCR-6.6.2.1.1    Screening Decision:   DP – W82, W84, W85, W86                                     SO-C – W83

                  SCR-6.6.2.1.2  Summary of New Information

                  SCR-6.6.2.1.3  Screening Argument

          SCR-6.6.3  Microbial Transport

              SCR-6.6.3.1    FEP Number:    W87 FEP Title:          Microbial Transport

                  SCR-6.6.3.1.1    Screening Decision:  UP

                  SCR-6.6.3.1.2  Summary of New Information

                  SCR-6.6.3.1.3  Screening Argument

              SCR-6.6.3.2    FEP Number:    W88 FEP Title:          Biofilms

                  SCR-6.6.3.2.1  Screening Decision:  SO-C Beneficial

                  SCR-6.6.3.2.2  Summary of New Information

                  SCR-6.6.3.2.3  Screening Argument

          SCR-6.6.4  Gas Transport

              SCR-6.6.4.1    FEP Number:    W89 FEP Title:          Transport of Radioactive Gases

                  SCR-6.6.4.1.1  Screening Decision:  SO-C

                  SCR-6.6.4.1.2  Summary of New Information

                  SCR-6.6.4.1.3  Screening Argument

      SCR-6.7  Contaminant Transport Processes

          SCR-6.7.1  Advection

              SCR-6.7.1.1    FEP Number:    W90 FEP Title:          Advection

                  SCR-6.7.1.1.1  Screening Decision:  UP

                  SCR-6.7.1.1.2  Summary of New Information

                  SCR-6.7.1.1.3  Screening Argument

          SCR-6.7.2  Diffusion

              SCR-6.7.2.1    FEP Numbers:   W91 and W92 FEP Titles:        Diffusion(W91)                           Matrix Diffusion (W92)

                  SCR-6.7.2.1.1  Screening Decision:  UP

                  SCR-6.7.2.1.2  Summary of New Information

                  SCR-6.7.2.1.3  Screening Argument

          SCR-6.7.3  Thermochemical Transport Phenomena

              SCR-6.7.3.1    FEP Number:    W93 FEP Title:          Soret Effect

                  SCR-6.7.3.1.1  Screening Decision:  SO-C

                  SCR-6.7.3.1.2  Summary of New Information

                  SCR-6.7.3.1.3  Screening Argument

          SCR-6.7.4  Electrochemical Transport Phenomena

              SCR-6.7.4.1    FEP Number:    W94 FEP Title:          Electrochemical Effects

                  SCR-6.7.4.1.1  Screening Decision:  SO-C

                  SCR-6.7.4.1.2  Summary of New Information

                  SCR-6.7.4.1.3  Screening Argument

              SCR-6.7.4.2    FEP Number:    W95 FEP Title:          Galvanic Coupling (outside the repository)

                  SCR-6.7.4.2.1  Screening Decision:  SO-P

                  SCR-6.7.4.2.2  Summary of New Information

                  SCR-6.7.4.2.3  Screening Argument

              SCR-6.7.4.3    FEP Number:    W96 FEP Title:          Electrophoresis

                  SCR-6.7.4.3.1  Screening Decision:  SO-C

                  SCR-6.7.4.3.2  Summary of New Information

                  SCR-6.7.4.3.3  Screening Argument

          SCR-6.7.5  Physiochemical Transport Phenomena

              SCR-6.7.5.1    FEP Number:    W97 FEP Title:          Chemical Gradients

                  SCR-6.7.5.1.1  Screening Decision:  SO-C

                  SCR-6.7.5.1.2  Summary of New Information

                  SCR-6.7.5.1.3  Screening Argument

              SCR-6.7.5.2    FEP Number:    W98 FEP Title:          Osmotic Processes

                  SCR-6.7.5.2.1  Screening Decision:  SO-C

                  SCR-6.7.5.2.2  Summary of New Information

                  SCR-6.7.5.2.3  Screening Argument

              SCR-6.7.5.3    FEP Number:    W99 FEP Title:          Alpha Recoil

                  SCR-6.7.5.3.1  Screening Decision:  SO-C

                  SCR-6.7.5.3.2  Summary of New Information

                  SCR-6.7.5.3.3  Screening Argument

              SCR-6.7.5.4    FEP Number:    W100 FEP Title:          Enhanced Diffusion

                  SCR-6.7.5.4.1  Screening Decision:  SO-C

                  SCR-6.7.5.4.2  Summary of New Information

                  SCR-6.7.5.4.3  Screening Argument

      SCR-6.8  Ecological FEPs

          SCR-6.8.1  Plant, Animal, and Soil Uptake

              SCR-6.8.1.1    FEP Numbers:   W101, W102, and W103 FEP Titles:        Plant Uptake (W101)                           Animal Uptake (W102)                           Accumulation in Soils (W103)

                  SCR-6.8.1.1.1    Screening Decision:    SO-R for section 191.13 – W101, W102                                      SO-C Beneficial for section 191.13 – W103                                      SO-C for section 191.15 – W101, W102, W103

                  SCR-6.8.1.1.2  Summary of New Information

                  SCR-6.8.1.1.3  Screening Argument

          SCR-6.8.2  Human Uptake

              SCR-6.8.2.1    FEP Numbers:   W104, W105, W106, W107, and W108 FEP Titles:      Ingestion (W104)                         Inhalation (W105)                         Irradiation (W106)                         Dermal Sorption (W107)                         Injection (W108)

                  SCR-6.8.2.1.1    Screening Decision:    SO-R                                      SO-C for section 191.15

                  SCR-6.8.2.1.2  Summary of New Information

                  SCR-6.8.2.1.3  Screening Argument

  SCR-7.0  References

List of Figures

Figure SCR-1.   Diffusion Penetration Distance in the WIPP as a Function of Diffusion Time

List of Tables

Table SCR-1.  FEPs Change Summary Since CRA-2004

Table SCR-2.  FEPs Reassessment Results

Table SCR-3.  Delaware Basin Brine Well Status

Table SCR-4.  Changes in Inventory Quantities from the CCA to the CRA-2009

Table SCR-5.  CCA and CRA Exothermic Temperature Rises

 

 

Acronyms and Abbreviations

mm                   micrometer

AIC                 active institutional controls

BNL                Brookhaven National Laboratory

Bq                   becquerels

CAG                Compliance Application Guidance

CCA                Compliance Certification Application

CCDF              complementary cumulative distribution function

CDF                cumulative distribution function

CFR                 Code of Federal Regulations

CH-TRU          contact-handled transuranic

Ci                    curie

cm                   centimeter

CPD                Carlsbad Potash District

CRA                Compliance Recertification Application

DBDSP           Delaware Basin Drilling Surveillance Program

DFR                driving force ratio

DOE                U.S. Department of Energy

DP                   disturbed performance

DRZ                disturbed rock zone

EP                   event and process

EPA                 U.S. Environmental Protection Agency

ERMS             Electronic Record Management System

FEP                 feature, event, and process

FLAC              Fast Lagrangian Analysis Continua

FMT                Fracture-Matrix Transport

FSU                 Florida State University

ft                      foot

ft2                     square foot

ft3                     cubic foot

g                      gram

gal                   gallon

gpm                 gallons per minute

H                     human-initiated

HCN                historic, current, and near-future

hr                     hour

IB                    inside boundary

in                     inch

Kd                    retardation distribution coefficient

kg                    kilogram

kg/m3                         kilograms per cubic meter

km                   kilometer

km2                  square kilometer

kW                   kilowatt

L                      liter

lb/gal               pounds per gallon

LWA               Land Withdrawal Act

m                     meter

m2                    square meter

m3                    cubic meter

Ma BP             million years before present

MB                  marker bed

MeV                megaelectron volt

mi                    mile

mL                   milliliter

MPa                 megapascal

MPI                 Mississippi Potash Inc.

mV                   millivolt

N                     natural

NMBMMR      New Mexico Bureau of Mines and Mineral Resources

OB                   outside boundary

oz                    ounce

PA                   performance assessment

PABC              Performance Assessment Baseline Calculation

PAVT              Performance Assessment Verification Test

PIC                  passive institutional control

ppm                 parts per million

psi                   pounds per square inch

psia                 pounds per square inch absolute

RH-TRU          remote-handled transuranic

s                      second

SKI                  Statens Kärnkraftinspektion

SNL                 Sandia National Laboratories

SO-C               screened-out consequence

SO-P               screened-out probability

SO-R               screened-out regulatory

T field             transmissitivity field

TRU                transuranic

TSD                 Technical Support Document

TWBIR            Transuranic Waste Baseline Inventory Report

UP                   undisturbed performance

V                     volt

W                    waste and repository-induced

W                    watt

W/Ci               watts per curie

W/g                 watts per gram

WIPP               Waste Isolation Pilot Plant

WPO               WIPP Project Office

yd3                   cubic yard

yr                     year

Elements and Chemical Compounds

Al                    aluminum

Am                  americium

An                   actinide

C                     carbon

CH4                 methane

CO2                 carbon dioxide

Cs                    cesium

EDTA              ethylenediaminetetraacetate

Fe                    iron

MgO                magnesium oxide

Np                   neptunium

Pm                   promethium

Pu                    plutonium

Rn                    radon

Sr                    strontium

Th                    thorium

U                     uranium



The U.S. Department of Energy (DOE) has developed the Waste Isolation Pilot Plant (WIPP) in southeastern New Mexico for the disposal of transuranic (TRU) wastes generated by defense programs. In May of 1998, the U.S. Environmental Protection Agency (EPA) certified that the WIPP would meet the disposal standards (U.S. Environmental Protection Agency 1998a, p. 27405) established in 40 CFR Part 191 Subparts B and C (U.S. Environmental Protection Agency 1993), thereby allowing the WIPP to begin waste disposal operations.  This certification was based, in part, on performance assessment (PA) calculations that were included in the DOE’s Compliance Certification Application (CCA) (U.S. Department of Energy 1996).  These calculations demonstrate that the cumulative releases of radionuclides to the accessible environment will not exceed those allowed by the EPA standard.

The WIPP Land Withdrawal Act (LWA) (U.S. Congress 1992) requires the WIPP to be recertified (demonstrating continued compliance with the disposal standards) every five years.  As such, the DOE prepared the 2004 Compliance Recertification Application (CRA-2004) (U.S. Department of Energy 2004), which demonstrated that the WIPP complied with the EPA’s requirements for radioactive waste disposal.  The CRA-2004 included changes to the WIPP long-term compliance baseline since the CCA.  Similarly, and in compliance with the recertification rules, the DOE has prepared the 2009 Compliance Recertification Application (CRA-2009) that documents changes since the CRA-2004, and demonstrates compliance with the long-term disposal requirements of 40 CFR Part 191 and the compliance criteria of 40 CFR Part 194.

To assure that PA calculations account for important aspects of the disposal system, features, events, and processes (FEPs) considered to be potentially important to the disposal system are identified.  These FEPs are used as a tool for determining what phenomena and components of the disposal system can and should be dealt with in PA calculations.  For the WIPP CCA, a systematic process was used to compile, analyze, screen, and document FEPs for use in PA.  The FEP screening process used in the CCA, the CRA-2004, and the CRA-2009 is described in detail in the CCA, Chapter 6.0, Section 6.2.  For recertification applications, this process evaluates any new information that may have impacts on or present inconsistencies to those screening arguments and decisions presented since the last certification or recertification.  The FEPs baseline is managed according to Sandia Activity/Project Specific Procedure 9-4, Performing FEPs Baseline Impact Assessment for Planned or Unplanned Changes (Revision 1) (Kirkes 2006).  For the CRA-2009, a reassessment of FEPs concluded that of the 235 FEPs considered for the CRA-2004, 188 have not been changed, 35 have been updated with new information, 10 have been split into 20 similar, but more descriptive FEPs, 1 screening argument has been changed to correct errors discovered during review, and 1 has had its screening decision changed.  Therefore, there are 245 WIPP FEPs for the CRA-2009.  Note that none of these new or updated FEPs require changes to PA models or codes; existing models represent these FEPs in their current configurations.

Table SCR-1 lists the FEPs that have been added, separated, or had screening decision changes since the CRA-2004.

Table SCR-1.  FEPs Change Summary Since CRA-2004

EPA FEP I.D.a,b

FEP Name

Summary of Change

FEPs Combined or Separated

H27

Liquid Waste Disposal – Outside Boundary (OB)

Name changed to “Liquid Waste Disposal Boundary – OB” to specify that this FEP pertains to those activities outside the WIPP land withdrawal boundary.

H28

Enhanced Oil and Gas Production – OB

Name changed to “Enhanced Oil and Gas Production – OB” to specify that this FEP pertains to those activities outside the WIPP land withdrawal boundary.

H29

Hydrocarbon Storage – OB

Name changed to “Hydrocarbon Storage – OB” to specify that this FEP pertains to those activities outside the WIPP land withdrawal boundary.

W6

Shaft Seal Geometry

Name changed to be specific to shaft seals, rather than generic “seals,” which also included panel closures (seals).

W7

Shaft Seal Physical Properties

Name changed to be specific to shaft seals, rather than generic “seals,” which also included panel closures (seals).

W8

Shaft Seal Chemical Composition

Name changed to be specific to shaft seals, rather than generic “seals,” which also included panel closures (seals).

W17

Radiological Effects on Shaft Seals

Name changed to be specific to shaft seals, rather than generic “seals,” which also included panel closures (seals).

W36

Consolidation of Shaft Seals

Name changed to be specific to shaft seals, rather than generic “seals,” which also included panel closures (seals).

W37

Mechanical Degradation of Shaft Seals

Name changed to be specific to shaft seals, rather than generic “seals,” which also included panel closures (seals).

W74

Chemical Degradation of Shaft Seals

Name changed to be specific to shaft seals, rather than generic “seals,” which also included panel closures (seals).

FEPs With Changed Screening Decisions

H41

Surface Disruptions

Screening changed from screened-out regulatory (SO-R) to screened-out consequence (SO-C) because of inconsistency with screening rationale.

New FEPs for CRA-2009

H60

Liquid Waste Disposal – Inside Boundary (IB)

New FEP; separated from H27.  The creation of this new FEP allows for more appropriate screening based on regulatory provisions pertaining to activities within the WIPP land withdrawal boundary.

H61

Enhanced Oil and Gas Production – IB

New FEP; separated from H28.  The creation of this new FEP allows for more appropriate screening based on regulatory provisions that pertain to activities within the WIPP land withdrawal boundary.

H62

Hydrocarbon Storage – IB

New FEP; separated from H29.  The creation of this new FEP allows for more appropriate screening based on regulatory provisions that pertain to activities within the WIPP land withdrawal boundary.

a  H = Human-induced FEP.

b  W = Waste and Repository-Induced FEP.

 

Table SCR-1.  FEPs Change Summary Since CRA-2004 (Continued)

EPA FEP I.D.a,b

FEP Name

Summary of Change

W109

Panel Closure Geometry

New FEP; separated from W6.  The creation of this new FEP allows for more appropriate screening based on potential differences in design and composition of shaft seals versus panel closures.

W110

Panel Closure Physical Properties

New FEP; separated from W7.  The creation of this new FEP allows for more appropriate screening based on potential differences in design and composition of shaft seals versus panel closures.

W111

Panel Closure Chemical Composition

New FEP; separated from W8.  The creation of this new FEP allows for more appropriate screening based on potential differences in design and composition of shaft seals versus panel closures.

W112

Radiological Effects on Panel Closures

New FEP; separated from W17.  The creation of this new FEP allows for more appropriate screening based on potential differences in design and composition of shaft seals versus panel closures.

W113

Consolidation of Panel Closures

New FEP; separated from W36.  The creation of this new FEP allows for more appropriate screening based on potential differences in design and composition of shaft seals versus panel closures.

W114

Mechanical Degradation of Panel Closures

New FEP; separated from W37.  The creation of this new FEP allows for more appropriate screening based on potential differences in design and composition of shaft seals versus panel closures.

W115

Chemical Degradation of Panel Closures

New FEP; separated from W74.  The creation of this new FEP allows for more appropriate screening based on potential differences in design and composition of shaft seals versus panel closures.

a  H = Human-induced FEP.

b  W = Waste and Repository-Induced FEP.

 


The origin of FEPs is related to the EPA’s radioactive waste disposal standard’s requirement to use PA methodology.  The DOE was required to demonstrate that the WIPP complied with the containment requirements of 40 CFR § 191.13 (U.S. Environmental Protection Agency 1993).  These requirements state that the DOE must use PA to demonstrate that the probabilities of cumulative radionuclide releases from the disposal system during the 10,000 years following closure will fall below specified limits.  The PA analyses supporting this determination must be quantitative and must consider uncertainties caused by all significant processes and events that may affect the disposal system, including inadvertent human intrusion into the repository during the future.  The scope of PA is further defined by the EPA at 40 CFR § 194.32 (U.S. Environmental Protection Agency 1996a), which states,

Any compliance application(s) shall include information which:

(1)  Identifies all potential processes, events or sequences and combinations of processes and events that may occur during the regulatory time frame and may affect the disposal system;

(2)  Identifies the processes, events or sequences and combinations of processes and events included in performance assessments; and

(3)  Documents why any processes, events or sequences and combinations of processes and events identified pursuant to paragraph (e)(1) of this section were not included in performance assessment results provided in any compliance application.

Therefore, the PA methodology includes a process that compiles a comprehensive list of the FEPs that are potentially relevant to disposal system performance.  Those FEPs shown by screening analysis to have the potential to affect performance are represented in scenarios and quantitative calculations using a system of linked computer models to describe the interaction of the repository with the natural system, both with and without human intrusion.  For the CCA, the DOE first compiled a comprehensive list of FEPs, which was then subjected to a screening process that eventually lead to the set of FEPs used in PA to demonstrate the WIPP’s compliance with the long-term disposal standards.

As a starting point, the DOE assembled a list of potentially relevant FEPs from the compilation developed by Stenhouse, Chapman, and Sumerling (1993) for the Swedish Nuclear Power Inspectorate (Statens Kärnkraftinspektion, or SKI). The SKI list was based on a series of FEP lists developed for other disposal programs and is considered the best-documented and most comprehensive starting point for the WIPP.  For the SKI study, an initial raw FEP list was compiled based on nine different FEP identification studies.

The compilers of the SKI list eliminated a number of FEPs as irrelevant to the particular disposal concept under consideration in Sweden.  These FEPs were reinstated for the WIPP effort, and several FEPs on the SKI list were subdivided to facilitate screening for the WIPP.  Finally, to ensure comprehensiveness, other FEPs specific to the WIPP were added based on review of key project documents and broad examination of the preliminary WIPP list by both project participants and stakeholders.  The initial unedited list is contained in the CCA, Appendix SCR, Attachment 1.  The initial unedited FEP list was restructured and revised to derive the comprehensive WIPP FEP list used in the CCA.  The number of FEPs was reduced to 237 in the CCA to eliminate the ambiguities presented in a generic list.  Restructuring the list did not remove any substantive issues from the discussion.  As discussed in more detail in the CCA, Appendix SCR, Attachment 1, the following steps were used to reduce the initial unedited list to the appropriate WIPP FEP list used in the CCA.

·       References to subsystems were eliminated because the SKI subsystem classification was not appropriate for the WIPP disposal concept.  For example, in contrast to the Swedish disposal concept, canister integrity does not have a role in post-operational performance of the WIPP, and the terms near-field, far-field, and biosphere are not unequivocally defined for the WIPP site.

·       Duplicate FEPs were eliminated.  Duplicate FEPs arose in the SKI list because individual FEPs could act in different subsystems.  FEPs had a single entry in the CCA list whether they were applicable to several parts of the disposal system or to a single part only (for example, the FEP Gas Effects).  Disruption appears in the seals, backfill, waste, canister, and near-field subsystems in the initial FEP list.  These FEPs are represented by a single FEP, Disruption Due to Gas Effects.

·       FEPs that are not relevant to the WIPP design or inventory were eliminated.  Examples include FEPs related to high-level waste, copper canisters, and bentonite backfill.

·       FEPs relating to engineering design changes were eliminated because they were not relevant to a compliance application based on the DOE’s design for the WIPP.

·       FEPs relating to constructional, operational, and decommissioning errors were eliminated.  The DOE has administrative and quality control procedures to ensure that the facility will be constructed, operated, and decommissioned properly.

·       Detailed FEPs relating to processes in the surface environment were aggregated into a small number of generalized FEPs.  For example, the SKI list includes the biosphere FEPs Inhalation of Salt Particles, Smoking, Showers and Humidifiers, Inhalation and Biotic Material, Household Dust and Fumes, Deposition (Wet and Dry), Inhalation and Soils and Sediments, Inhalation and Gases and Vapors (Indoor and Outdoor), and Suspension in Air, which are represented by the FEP Inhalation.

·       FEPs relating to the containment of hazardous metals, volatile organic compounds, and other chemicals that are not regulated by Part 191 were not included.

·       A few FEPs have been renamed to be consistent with terms used to describe specific WIPP processes (for example, Wicking, Brine Inflow).

These steps resulted in a list of WIPP-relevant FEPs retained for further consideration in the first certification PA.  These FEPs were screened to determine which would be included in the PA models and scenarios for the CCA PA.

The purpose of FEP screening is to identify those FEPs that should be accounted for in PA calculations, and those FEPs that need not be considered further.  The DOE’s process of removing FEPs from consideration in PA calculations involved the structured application of explicit screening criteria.  The criteria used to screen out FEPs are explicit regulatory exclusion (SO-R), probability (SO-P), or consequence (SO-C).  All three criteria are derived from regulatory requirements.  FEPs not screened out as SO-R, SO-P, or SO-C were retained for inclusion in PA calculations and are classified as either undisturbed performance (UP) or disturbed performance (DP) FEPs.

Specific FEP screening criteria are stated in Part 191 and Part 194.  Such screening criteria relating to the applicability of particular FEPs represent screening decisions made by the EPA.  That is, in the process of developing and demonstrating the feasibility of the Part 191 standard and the Part 194 criteria, the EPA considered and made conclusions on the relevance, consequence, and probability of particular FEPs occurring.  In so doing, it allowed some FEPs to be eliminated from consideration.

Low-probability events can be excluded on the basis of the criterion provided in 40 CFR § 194.32(d), which states, “performance assessments need not consider processes and events that have less than one chance in 10,000 of occurring over 10,000 years.”  In practice, for most FEPs screened out on the basis of low probability of occurrence, it has not been possible to estimate a meaningful quantitative probability.  In the absence of quantitative probability estimates, a qualitative argument was used.

The DOE recognizes two uses for this criterion:

1.     FEPs can be eliminated from PA calculations on the basis of insignificant consequence.  Consequence can refer to effects on the repository or site or to radiological consequence.  In particular, 40 CFR § 194.34(a) (U.S. Environmental Protection Agency 1996a) states, “The results of performance assessments shall be assembled into ‘complementary, cumulative distribution functions’ (CCDFs) that represent the probability of exceeding various levels of cumulative release caused by all significant processes and events.”  The DOE has omitted events and processes (EPs) from PA calculations where there is a reasonable expectation that the remaining probability distribution of cumulative releases would not be significantly changed by such omissions.

2.     FEPs that are potentially beneficial to subsystem performance may be eliminated from PA calculations if necessary to simplify the analysis.  This argument may be used when there is uncertainty as to exactly how the FEP should be incorporated into assessment calculations or when incorporation would incur unreasonable difficulties.

In some cases, the effects of the particular event or process occurring, although not necessarily insignificant, can be shown to lie within the range of uncertainty of another FEP already accounted for in the PA calculations.  In such cases, the event or process may be included in PA calculations implicitly, within the range of uncertainty associated with the included FEP.

Although some FEPs could be eliminated from PA calculations on the basis of more than one criterion, the most practical screening criterion was used for classification.  In particular, a regulatory screening classification was used in preference to a probability or consequence screening classification.  FEPs that have not been screened out based on any of the three criteria were included in the PA.

FEPs classified as UP are accounted for in calculations of UP of the disposal system.  UP is defined in 40 CFR § 191.12 (U.S. Environmental Protection Agency 1993) as “the predicted behavior of a disposal system, including consideration of the uncertainties in predicted behavior, if the disposal system is not disrupted by human intrusion or the occurrence of unlikely natural events.”  The UP FEPs are accounted for in the PA calculations to evaluate compliance with the containment requirements in section 191.13.  Undisturbed PA calculations are also used to demonstrate compliance with the individual and groundwater protection requirements of 40 CFR § 191.15 (U.S. Environmental Protection Agency 1993) and Part 191 Subpart C, respectively.

The FEPs classified as DP are accounted for only in assessment calculations for DP.  The DP FEPs that remain following the screening process relate to the potential disruptive effects of future drilling and mining events in the controlled area.  Consideration of both DP and UP FEPs is required to evaluate compliance with section 191.13.

In the following sections, FEPs are discussed under the categories Natural FEPs, Human-Induced EPs, and Waste- and Repository-Induced FEPs.  (IDs of Natural FEPs begin with “N,” and IDs of Waste- and Repository-Induced FEPs begin with “W.”)  The FEPs are also considered within time frames during which they may occur.  Because of the regulatory requirements concerning human activities, two time periods were used when evaluating human-induced EPs.  These time frames were defined as Historical, Current, and Near-Future Human Activities (HCN) and Future Human Activities (Future). These time frames are also discussed in the following section.

Natural FEPs are those that relate to hydrologic, geologic, and climate conditions that have the potential to affect long-term performance of the WIPP disposal system over the regulatory time frame.  These FEPs do not include the impacts of other human-related activities such as the effect of boreholes on FEPs related to natural changes in groundwater chemistry.  Only natural FEPs are included in the screening process.

Consistent with section 194.32(d), the DOE has screened out several natural FEPs from PA calculations on the basis of a low probability of occurrence at or near the WIPP site.  In particular, natural events for which there is no evidence indicating that they have occurred within the Delaware Basin have been screened on this basis.  For FEPs analysis, the probabilities of occurrence of these events are assumed to be zero.  Quantitative, nonzero probabilities for such events, based on numbers of occurrences, cannot be ascribed without considering regions much larger than the Delaware Basin, thus neglecting established geological understanding of the FEPs that occur within particular geographical provinces.

In considering the overall geological setting of the Delaware Basin, the DOE has eliminated many FEPs from PA calculations on the basis of low consequence.  FEPs that have had little effect on the characteristics of the region in the past are expected to be of low consequence for the regulatory time period.

Human-induced EPs (Human EPs) are those associated with human activities in the past, present, and future.  The EPA provided guidance in their regulations concerning which human activities are to be considered, their severity, and the manner in which to include them in the future predictions.

The scope of PAs is clarified with respect to human-induced EPs in section 194.32.  At 40 CFR § 194.32(a), the EPA states,

Performance assessments shall consider natural processes and events, mining, deep drilling, and shallow drilling that may affect the disposal system during the regulatory time frame.

Thus PAs must include consideration of human-induced EPs relating to mining and drilling activities that might take place during the regulatory time frame.  In particular, PAs must consider the potential effects of such activities that might take place within the controlled area at a time when institutional controls cannot be assumed to completely eliminate the possibility of human intrusion.

Further criteria concerning the scope of PAs are provided at 40 CFR § 194.32(c):

Performance assessments shall include an analysis of the effects on the disposal system of any activities that occur in the vicinity of the disposal system prior to disposal and are expected to occur in the vicinity of the disposal system soon after disposal.  Such activities shall include, but shall not be limited to, existing boreholes and the development of any existing leases that can be reasonably expected to be developed in the near future, including boreholes and leases that may be used for fluid injection activities.

In order to implement the criteria in section 194.32 relating to the scope of PAs, the DOE has divided human activities into three categories:  (1) human activities currently taking place and those that took place prior to the time of the compliance application, (2) human activities that might be initiated in the near future after submission of the compliance application, and (3) human activities that might be initiated after repository closure.  The first two categories of EPs, corresponding to the HCN time frame, are considered under UP, and EPs in the third category, which belong to the Future time frame, may lead to DP conditions.  A description of these three categories follows.

1.     Historical and current human activities include resource-extraction activities that have historically taken place and are currently taking place outside the controlled area.  These activities are of potential significance insofar as they could affect the geological, hydrological, or geochemical characteristics of the disposal system or groundwater flow pathways outside the disposal system.  Current human activities taking place within the controlled area are essentially those associated with development of the WIPP repository.  Historic human activities include existing boreholes.

2.     Near-future human activities include resource-extraction activities that may be expected to occur outside the controlled area based on existing plans and leases.  Thus the near future includes the expected lives of existing mines and oil and gas fields, and the expected lives of new mines and oil and gas fields that the DOE expects will be developed based on existing plans and leases.  These activities are of potential significance insofar as they could affect the geological, hydrological, or geochemical characteristics of the disposal system or groundwater flow pathways outside the disposal system.  The only human activities expected to occur within the controlled area in the near future are those associated with development of the WIPP repository.  The DOE expects that any activity initiated in the near future, based on existing plans and leases, will be initiated prior to repository closure.  Activities initiated prior to repository closure are assumed to continue until their completion.

3.     Future human activities include activities that might be initiated within or outside the controlled area after repository closure.  This includes drilling and mining for resources within the disposal system at a time when institutional controls cannot be assumed to completely eliminate the possibility of such activities.  Future human activities could influence the transport of contaminants within and outside the disposal system by directly removing waste from the disposal system or altering the geological, hydrological, or geochemical characteristics of the disposal system.

PAs must consider the effects of future human activities on the performance of the disposal system.  The EPA has provided criteria relating to future human activities in section 194.32(a), which limits the scope of consideration of future human activities in PAs to mining and drilling.

The EPA provides the following additional criteria concerning the type of future mining that should be considered by the DOE in 40 CFR § 194.32(b):

Assessments of mining effects may be limited to changes in the hydraulic conductivity of the hydrogeologic units of the disposal system from excavation mining for natural resources.  Mining shall be assumed to occur with a one in 100 probability in each century of the regulatory time frame. Performance assessments shall assume that mineral deposits of those resources, similar in quality and type to those resources currently extracted from the Delaware Basin, will be completely removed from the controlled area during the century in which such mining is randomly calculated to occur.  Complete removal of such mineral resources shall be assumed to occur only once during the regulatory time frame.

Thus consideration of future mining may be limited to mining within the controlled area at the locations of resources that are similar in quality and type to those currently extracted from the Delaware Basin.  Potash is the only resource that has been identified within the controlled area in quality similar to that currently mined from underground deposits elsewhere in the Delaware Basin.  The hydrogeological impacts of future potash mining within the controlled area are accounted for in calculations of the DP of the disposal system.  Consistent with section 194.32(b), all economically recoverable resources in the vicinity of the disposal system (outside the controlled area) are assumed to be extracted in the near future.

With respect to consideration of future drilling, in the preamble to Part 194, the EPA

…reasoned that while the resources drilled for today may not be the same as those drilled for in the future, the present rates at which these boreholes are drilled can nonetheless provide an estimate of the future rate at which boreholes will be drilled.

Criteria concerning the consideration of future deep and shallow drilling in PAs are provided in 40 CFR § 194.33 (U.S. Environmental Protection Agency 1996a).  The EPA also provides a criterion in 40 CFR § 194.33(d) concerning the use of future boreholes subsequent to drilling:

With respect to future drilling events, performance assessments need not analyze the effects of techniques used for resource recovery subsequent to the drilling of the borehole.

Thus PAs need not consider the effects of techniques used for resource extraction and recovery that would occur subsequent to the drilling of a borehole in the future.  Theses activities are screened SO-R.

The EPA provides an additional criterion that limits the severity of human intrusion scenarios that must be considered in PAs.  In 40 CFR § 194.33(b)(1) the EPA states,

Inadvertent and intermittent intrusion by drilling for resources (other than those resources provided by the waste in the disposal system or engineered barriers designed to isolate such waste) is the most severe human intrusion scenario.

Future Human EPs accounted for in PA calculations for the WIPP are those associated with mining and deep drilling within the controlled area at a time when institutional controls cannot be assumed to completely eliminate the possibility of such activities.  All other future Human EPs, if not eliminated from PA calculations based on regulation, have been eliminated based on low consequence or low probability.  For example, the effects of future shallow drilling within the controlled area were eliminated from CCA PA calculations on the basis of low consequence to the performance of the disposal system.

The waste- and repository-induced FEPs are those that relate specifically to the waste material, waste containers, shaft seals, magnesium oxide (MgO) backfill, panel closures, repository structures, and investigation boreholes.  All FEPs related to radionuclide chemistry and radionuclide migration are included in this category. The FEPs related to radionuclide transport resulting from future borehole intersections of the WIPP excavation are defined as waste- and repository-induced FEPs.


The reassessment of FEPs (Kirkes 2008) results in a new FEPs baseline for CRA-2009.  As discussed in Section SCR-1.0, 189 of the 235 WIPP FEPs have not changed since the CRA-2004.  However, 35 FEPs required updates to their FEP descriptions and/or screening arguments, 10 FEPs have been split into 20 similar but more descriptive FEPs, and 1 FEP has had its screening decision changed.  The single screening decision change does not result in a new FEP incorporated into PA calculations; the FEP continues to be screened out of PA.  Thus the CRA-2009 evaluates 245 WIPP FEPs.

Table SCR-2 outlines the results of the assessment, and subsequent sections of this document present the actual screening decisions and supporting arguments.  Those FEPs not separated by gridlines in the first column of Table SCR-2 have been addressed by group because of close similarity with other FEPs within that group.  This grouping process was formerly used in the CCA and also by the EPA in their Technical Support Document (TSD) for section 194.32 (U.S. Environmental Protection Agency 1998b).


Table SCR-2.  FEPs Reassessment Results

EPA FEP I.D.a,b,c

FEP Name

Screening Decision Changed

Change Summary

Screening Classification

N1

Stratigraphy

No

No change.

UP

N2

Brine Reservoirs

No

No change.

DP

N3

Changes in Regional Stress

No

No change.

SO-C

N4

Regional Tectonics

No

No change.

SO-C

N5

Regional Uplift and Subsidence

No

No change.

SO-C

N6

Salt Deformation

No

No change.

SO-P

N7

Diapirism

No

No change.

SO-P

N8

Formation of Fractures

No

No change.

SO-P
UP (Repository)

N9

Changes in Fracture Properties

No

No change.

SO-C
UP (Near Repository)

N10

Formation of New Faults

No

No change.

SO-P

N11

Fault Movement

No

No change.

SO-P

N12

Seismic Activity

No

Updated with new seismic data.

UP

N13

Volcanic Activity

No

No change.

SO-P

N14

Magmatic Activity

No

No change.

SO-C

N15

Metamorphic Activity

No

No change.

SO-P

N16

Shallow Dissolution

No

No change.

UP

 

a N = Natural FEP

b H = Human-induced EP

c W = Waste- and Repository-Induced FEP

 


Table SCR-2.  FEPs Reassessment Results (Continued)

EPA FEP I.D.a,b,c

FEP Name

Screening Decision Changed

Change Summary

Screening Classification

N18

Deep Dissolution

No

No change.

SO-P

N20

Breccia Pipes

No

No change.

SO-P

N21

Collapse Breccias

No

No change.

SO-P

N22

Fracture Infills

No

No change.

SO-C - Beneficial

N23

Saturated Groundwater Flow

No

No change.

UP

N24

Unsaturated Groundwater Flow

No

No change.

UP

N25

Fracture Flow

No

No change.

UP

N27

Effects of Preferential Pathways

No

No change.

UP

N26

Density effects on Groundwater Flow

No

No change.

SO-C

N28

Thermal effects on Groundwater Flow

No

No change.

SO-C

N29

Saline Intrusion [Hydrogeological Effects]

No

No change.

SO-P

N30

Freshwater Intrusion [Hydrogeological effects]

No

No change.

SO-P

N31

Hydrological Response to Earthquakes

No

No change.

SO-C

N32

Natural Gas Intrusion

No

No change.

SO-P

N33

Groundwater Geochemistry

No

No change.

UP

N34

Saline Intrusion (Geochemical Effects)

No

No change.

SO-C

N38

Effects of Dissolution

No

No change.

SO-C

N35

Freshwater Intrusion (Geochemical Effects)

No

No change.

SO-C

N36

Changes in Groundwater Eh

No

No change.

SO-C

N37

Changes in Groundwater pH

No

No change.

SO-C

N39

Physiography

No

No change.

UP

N40

Impact of a Large Meteorite

No

Errors identified in screening argument corrected; no change in screening decision.

SO-P

N41

Mechanical Weathering

No

No change.

SO-C

N42

Chemical Weathering

No

No change.

SO-C

N43

Aeolian Erosion

No

No change.

SO-C

 

a N = Natural FEP

b H = Human-induced EP

c W = Waste- and Repository-Induced FEP

 


Table SCR-2.  FEPs Reassessment Results (Continued)

EPA FEP I.D.a,b,c

FEP Name

Screening Decision Changed

Change Summary

Screening Classification

N44

Fluvial Erosion

No

No change.

SO-C

N45

Mass Wasting [Erosion]

No

No change.

SO-C

N46

Aeolian Deposition

No

No change.

SO-C

N47

Fluvial Deposition

No

No change.

SO-C

N48

Lacustrine Deposition

No

No change.

SO-C

N49

Mass Wasting [Deposition]

No

No change.

SO-C

N50

Soil Development

No

No change.

SO-C

N51

Stream and River Flow

No

No change.

SO-C

N52

Surface Water Bodies

No

No change.

SO-C

N53

Groundwater Discharge

No

No change.

UP

N54

Groundwater Recharge

No

No change.

UP

N55

Infiltration

No

No change.

UP

N56

Changes in Groundwater Recharge and Discharge

No

No change.

UP

N57

Lake Formation

No

No change.

SO-C

N58

River Flooding

No

No change.

SO-C

N59

Precipitation (e.g. Rainfall)

No

No change.

UP

N60

Temperature

No

No change.

UP

N61

Climate Change

No

No change.

UP

N62

Glaciation

No

No change.

SO-P

N63

Permafrost

No

No change.

SO-P

N64

Seas and Oceans

No

No change.

SO-C

N65

Estuaries

No

No change.

SO-C

N66

Coastal Erosion

No

No change.

SO-C

N67

Marine Sediment Transport and Deposition

No

No change.

SO-C

N68

Sea Level Changes

No

No change.

SO-C

N69

Plants

No

No change.

SO-C

N70

Animals

No

No change.

SO-C

N71

Microbes

No

No change.

SO-C
(UP - for colloidal effects and gas generation)

N72

Natural Ecological Development

No

No change.

SO-C

 

a N = Natural FEP

b H = Human-induced EP

c W = Waste- and Repository-Induced FEP

 


Table SCR-2.  FEPs Reassessment Results (Continued)

EPA FEP I.D.a,b,c

FEP Name

Screening Decision Changed

Change Summary

Screening Classification

H1

Oil and Gas Exploration

No

No change.

SO-C (HCN)
DP (Future)

H2

Potash Exploration

No

No change.

SO-C (HCN)
DP (Future)

H4

Oil and Gas Exploitation

No

No change.

SO-C (HCN)
DP (Future)

H8

Other Resources

No

No change.

SO-C (HCN)
DP (Future)

H9

Enhanced Oil and Gas Recovery

No

No change.

SO-C (HCN)
DP (Future)

H3

Water Resources Exploration

No

Updated with most recent monitoring information.

SO-C (HCN)
SO-C (Future)

H5

Groundwater Exploitation

No

Updated with most recent monitoring information.

SO-C (HCN)
SO-C (Future)

H6

Archaeological Investigations

No

No change.

SO-R (HCN)
SO-R (Future)

H7

Geothermal

No

No change.

SO-R (HCN)
SO-R (Future)

H10

Liquid Waste Disposal

No

No change.

SO-R (HCN)
SO-R (Future)

H11

Hydrocarbon Storage

No

No change.

SO-R (HCN)
SO-R (Future)

H12

Deliberate Drilling Intrusion

No

No change.

SO-R (HCN)
SO-R (Future)

H13

Conventional Underground Potash Mining

No

No change.

UP (HCN)
DP (Future)

H14

Other Resources (mining for)

No

No change.

SO-C (HCN)
SO-R (Future)

H15

Tunneling

No

No change.

SO-R (HCN)
SO-R (Future)

H16

Construction of Underground Facilities (for Example Storage, Disposal, Accommodation)

No

No change.

SO-R (HCN)
SO-R (Future)

H17

Archaeological Excavations

No

No change.

SO-C (HCN)
SO-R (Future)

H18

Deliberate Mining Intrusion

No

No change.

SO-R (HCN)
SO-R (Future)

 

a N = Natural FEP

b H = Human-induced EP

c W = Waste- and Repository-Induced FEP

 


Table SCR-2.  FEPs Reassessment Results (Continued)

EPA FEP I.D.a,b,c

FEP Name

Screening Decision Changed

Change Summary

Screening Classification

H19

Explosions for Resource Recovery

No

No change.

SO-C (HCN)
SO-R (Future)

H20

Underground Nuclear Device Testing

No

No change.

SO-C (HCN)
SO-R (Future)

H21

Drilling Fluid Flow

No

Screening argument revised. 

SO-C (HCN)
DP (Future)

H22

Drilling Fluid Loss

No

Screening argument revised.

SO-C (HCN)
DP (Future)

H23

Blowouts

No

No change.

SO-C (HCN)
DP (Future)

H24

Drilling-Induced Geochemical Changes

No

No change.

UP (HCN)
DP (Future)

H25

Oil and Gas Extraction

No

Screening argument updated.

SO-C (HCN)
SO-R (Future)

H26

Groundwater Extraction

No

Screening argument updated.

SO-C (HCN)
SO-R (Future)

H27

Liquid Waste Disposal–OB

No

FEP title has been modified to show that this event or process specifically applies to activities outside the WIPP boundary.  Screening argument has also been updated with new information.

SO-C (HCN)
SO-C (Future)

H28

Enhanced Oil and Gas Production–OB

No

FEP title has been modified to show that this event or process specifically applies to activities outside the WIPP boundary. Screening argument has also been updated with new information.

SO-C (HCN)
SO-C (Future)

H29

Hydrocarbon Storage–OB

No

FEP title has been modified to show that this event or process specifically applies to activities outside the WIPP boundary.  Screening argument has also been updated with new information.

SO-C (HCN)
SO-C (Future)

 

a N = Natural FEP

b H = Human-induced EP

c W = Waste- and Repository-induced FEP

 


Table SCR-2.  FEPs Reassessment Results (Continued)

EPA FEP I.D.a,b,c

FEP Name

Screening Decision Changed

Change Summary

Screening Classification

H60

Liquid Waste Disposal–IB

N/A – new FEP

This is a new FEP that is similar to H27, except that it specifically applies to activities inside the WIPP boundary.

SO-R (HCN)
SO-R (Future)

H61

Enhanced Oil and Gas Production–IB

N/A – new FEP

This is a new FEP that is similar to H28, except that it specifically applies to activities inside the WIPP boundary.

SO-R (HCN)
SO-R (Future)

H62

Hydrocarbon Storage–IB

N/A – new FEP

This is a new FEP that is similar to H29, except that it specifically applies to activities inside the WIPP boundary.

SO-R (HCN)
SO-R (Future)

H30

Fluid-injection Induced Geochemical Changes

No

No change.

UP (HCN)
SO-R (Future)

H31

Natural Borehole Fluid Flow

No

No change.

SO-C (HCN)
SO-C (Future, holes not penetrating waste panels)
DP (Future, holes penetrating panels)

H32

Waste-Induced Borehole Flow

No

No change.

SO-R (HCN)
DP (Future)

H34

Borehole-Induced Solution and Subsidence

No

No change.

SO-C (HCN)
SO-C (Future)

H35

Borehole-Induced Mineralization

No

No change.

SO-C (HCN)
SO-C (Future)

H36

Borehole-Induced Geochemical Changes

No

No change.

UP (HCN)
DP (Future)

SO-C (for units other than the Culebra)

H37

Changes in Groundwater Flow Due to Mining

No

No change.

UP (HCN)
DP (Future)

H38

Changes in Geochemistry Due to Mining

No

No change.

SO-C (HCN)
SO-R (Future)

 

a N = Natural FEP

b H = Human-induced EP

c W = Waste- and Repository-induced FEP

 


Table SCR-2.  FEPs Reassessment Results (Continued)

EPA FEP I.D.a,b,c

FEP Name

Screening Decision Changed

Change Summary

Screening Classification

H39

Changes in Groundwater Flow Due to Explosions

No

No change.

SO-C (HCN)
SO-R (Future)

H40

Land Use Changes

No

No change.

SO-R (HCN)
SO-R (Future)

H41

Surface Disruptions

Yes

Screening decision changed from SO-R to SO-C to remove inconsistency with rationale.

UP (HCN)
SO-C (Future)

H42

Damming of Streams or Rivers

No

No change.

SO-C (HCN)
SO-R (Future)

H43

Reservoirs

No

No change.

SO-C (HCN)
SO-R (Future)

H44

Irrigation

No

No change.

SO-C (HCN)
SO-R (Future)

H45

Lake Usage

No

No change.

SO-R (HCN)
SO-R (Future)

H46

Altered Soil or Surface Water Chemistry by Human Activities

No

No change.

SO-C (HCN)
SO-R (Future)

H47

Greenhouse Gas Effects

No

No change.

SO-R (HCN)
SO-R (Future)

H48

Acid Rain

No

No change.

SO-R (HCN)
SO-R (Future)

H49

Damage to the Ozone Layer

No

No change.

SO-R (HCN)
SO-R (Future)

H50

Coastal Water Use

No

No change.

SO-R (HCN)
SO-R (Future)

H51

Sea water Use

No

No change.

SO-R (HCN)
SO-R (Future)

H52

Estuarine Water Use

No

No change.

SO-R (HCN)
SO-R (Future)

H53

Arable Farming

No

No change.

SO-C (HCN)
SO-R (Future)

H54

Ranching

No

No change.

SO-C (HCN)
SO-R (Future)

H55

Fish Farming

No

No change.

SO-R (HCN)
SO-R (Future)

H56

Demographic Change and Urban Development

No

No change.

SO-R (HCN)
SO-R (Future)

 

a N = Natural FEP

b H = Human-induced EP

c W = Waste- and Repository-induced FEP

 


Table SCR-2.  FEPs Reassessment Results (Continued)

EPA FEP I.D.a,b,c

FEP Name

Screening Decision Changed

Change Summary

Screening Classification

H57

Loss of Records

No

No change.

NA (HCN)
DP (Future)

H58

Solution Mining for Potash

No

Updated with information regarding solution activities and plans in the region.

SO-R (HCN)
SO-R (Future)

H59

Solution Mining for Other Resources

No

Updated with new information regarding brine wells in the region.

SO-C (HCN)
SO-C (Future)

W1

Disposal Geometry

No

No change.

UP

W2

Waste Inventory

No

Updated to reflect the inventory data sources used for the CRA-2009 PA.

UP

W3

Heterogeneity of Waste Forms

No

Updated to reflect the inventory data sources used for the CRA-2009 PA.

DP

W4

Container Form

No

Updated to reflect the inventory data sources used for the CRA-2009 PA.

SO-C – Beneficial

W5

Container Material Inventory

No

No change.

UP

W6

Shaft Seal Geometry

No

Title changed to be specific to shaft seals.

UP

W7

Shaft Seal Physical Properties

No

Title changed to be specific to shaft seals. 

UP

W109

Panel Closure Geometry

N/A – new FEP.

Split from W6 to be specific to panel closures.

UP

W110

Panel Closure Physical Properties

N/A – new FEP

Split from W7 to be specific to panel closures.

UP

W8

Shaft Seal Chemical Composition

No

Title changed to be specific to shaft seals.

SO-C Beneficial

W111

Panel Closure Chemical Composition

N/A – new FEP

Split from W8 to be specific to panel closures.

SO-C Beneficial

 

a N = Natural FEP

b H = Human-induced EP

c W = Waste- and Repository-induced FEP

 


Table SCR-2.  FEPs Reassessment Results (Continued)

EPA FEP I.D.a,b,c

FEP Name

Screening Decision Changed

Change Summary

Screening Classification

W9

Backfill Physical Properties

No

No change.

SO–C

W10

Backfill Chemical Composition

No

No change.

UP

W11

Post-Closure Monitoring

No

No change.

SO-C

W12

Radionuclide Decay and In-Growth

No

No change.

UP

W13

Heat from Radioactive Decay

No

Updated to reflect the inventory used for the CRA-2009 PA.

SO-C

W14

Nuclear Criticality:  Heat

No

Updated to reflect the inventory used for the CRA-2009 PA.

SO-P

W15

Radiological Effects on Waste

No

Updated to reflect the inventory used for the CRA.

SO-C

W16

Radiological Effects on Containers

No

Updated to reflect the inventory used for the CRA.

SO-C

W17

Radiological Effects on Shaft Seals

No

FEP title changed to be specific to shaft seals; screening argument updated to reflect the inventory used for the CRA.

SO-C

W112

Radionuclide Effects on Panel Closures

N/A – new FEP

Split from W17 to be specific to panel closures.

SO-C

W18

Disturbed Rock Zone (DRZ)

No

No change.

UP

W19

Excavation-Induced Changes in Stress

No

No change.

UP

W20

Salt Creep

No

No change.

UP

W21

Changes in the Stress Field

No

No change.

UP

W22

Roof Falls

No

No change.

UP

W23

Subsidence

No

Source of subsidence monitoring data added.

SO-C

W24

Large Scale Rock Fracturing

No

Source of subsidence monitoring data added.

SO-P

W25

Disruption Due to Gas Effects

No

No change.

UP

W26

Pressurization

No

No change.

UP

 

a N = Natural FEP

b H = Human-induced EP

c W = Waste- and Repository-induced FEP

 


Table SCR-2.  FEPs Reassessment Results (Continued)

EPA FEP I.D.a,b,c

FEP Name

Screening Decision Changed

Change Summary

Screening Classification

W27

Gas Explosions

No

No change.

UP

W28

Nuclear Explosions

No

Updated to reflect the inventory used for the CRA-2009 PA.

SO-P

W29

Thermal Effects on Material Properties

No

Updated to reflect the inventory used for the CRA.  New thermal calculations added.

SO-C

W30

Thermally-Induced Stress Changes

No

Updated to reflect the inventory used for the CRA.  New thermal calculations added.

SO-C

W31

Differing Thermal Expansion of Repository Components

No

Updated to reflect the inventory used for the CRA.  New thermal calculations added.

SO-C

W72

Exothermic Reactions

No

Updated to reflect the inventory used for the CRA.  New thermal calculations added.

SO-C

W73

Concrete Hydration

No

Updated to reflect the inventory used for the CRA.  New thermal calculations added.

SO-C

W32

Consolidation of Waste

No

No change.

UP

W36

Consolidation of Shaft Seals

No

Title changed to be specific to shaft seals.

UP

W37

Mechanical Degradation of Shaft Seals

No

Title changed to be specific to shaft seals.

UP

W39

Underground Boreholes

No

No change.

UP

W113

Consolidation of Panel Closures

N/A – new FEP

Split from W36 to be specific to panel closures.

UP

W114

Mechanical Degradation of Panel Closures

N/A – new FEP

Split from W37 to be specific to panel closures.

UP

W33

Movement of Containers

No

Updated to reference new inventory data.

SO-C

W34

Container Integrity

No

No change.

SO–C Beneficial

a N = Natural FEP

b H = Human-induced EP

c W = Waste- and Repository-induced FEP

 


Table SCR-2.  FEPs Reassessment Results (Continued)

EPA FEP I.D.a,b,c

FEP Name

Screening Decision Changed

Change Summary

Screening Classification

W35

Mechanical Effects of Backfill

No

Screening argument updated to reflect reduction in MgO.

SO–C

W40

Brine Inflow

No

No change.

UP

W41

Wicking

No

No change.

UP

W42

Fluid Flow Due to Gas Production

No

No change.

UP

W43

Convection

No

No change.

SO-C

W44

Degradation of Organic Material

No

New thermal rise calculations referenced.

UP

W45

Effects of Temperature on Microbial Gas Generation

No

New thermal rise calculations referenced.

UP

W48

Effects of Biofilms on Microbial Gas Generation

No

New thermal rise calculations referenced.

UP

W46

Effects of Pressure on Microbial Gas Generation

No

No change.

SO-C

W47

Effects of Radiation on Microbial Gas Generation

No

Screening argument updated with new radionuclide inventory.

SO-C

W49

Gases from Metal Corrosion

No

No change.

UP

W51

Chemical Effects of Corrosion

No

No change.

UP

W50

Galvanic Coupling (Within the Repository)

No

No change.

SO-C

W52

Radiolysis of Brine

No

No change.

SO-C

W53

Radiolysis of Cellulose

No

Screening argument updated with new radionuclide inventory.

SO-C

W54

Helium Gas Production

No

Screening argument updated with new radionuclide inventory.

SO-C

W55

Radioactive Gases

No

Reference made to CRA-2009 inventory data.

SO-C

 

a N = Natural FEP

b H = Human-induced EP

c W = Waste- and Repository-induced FEP

 


Table SCR-2.  FEPs Reassessment Results (Continued)

EPA FEP I.D.a,b,c

FEP Name

Screening Decision Changed

Change Summary

Screening Classification

W56

Speciation

No

No change.

UP in disposal rooms and Culebra. SO-C elsewhere, and SO-C Beneficial in cementitious seals

W57

Kinetics of Speciation

No

No change.

SO-C

W58

Dissolution of Waste

No

No change.

UP

W59

Precipitation of Secondary Minerals

No

No change.

SO-C Beneficial

W60

Kinetics of Precipitation and Dissolution

No

No change.

SO-C

W61

Actinide Sorption

No

No change.

UP in the Culebra and Dewey Lake; SO-C—Beneficial in the disposal room, shaft seals, panel closures, and other geologic units.

W62

Kinetics of Sorption

No

No change.

UP in the Culebra and Dewey Lake; SO-C—Beneficial in the disposal room, shaft seals, panel closures, and other geologic units.

W63

Changes in Sorptive Surfaces

No

No change.

UP

W64

Effects of Metal Corrosion

No

No change.

UP

W66

Reduction-Oxidation Kinetics

No

No change.

UP

W65

Reduction-Oxidation Fronts

No

No change.

SO-P

W67

Localized Reducing Zones

No

No change.

SO-C

W68

Organic Complexation

No

No change.

UP

W69

Organic Ligands

No

No change.

UP

W71

Kinetics of Organic Complexation

No

No change.

SO-C

W70

Humic and Fulvic Acids

No

No change.

UP

 

a N = Natural FEP

b H = Human-induced EP

c W = Waste- and Repository-induced FEP

 


Table SCR-2.  FEPs Reassessment Results (Continued)

EPA FEP I.D.a,b,c

FEP Name

Screening Decision Changed

Change Summary

Screening Classification

W74

Chemical Degradation of Shaft Seals

No

Title changed to be specific to shaft seals.

UP

W76

Microbial Growth on Concrete

No

No change.

UP

W115

Chemical Degradation of Panel Closures

N/A – new FEP

Split from W74 to be specific to panel closures.

UP

W75

Chemical Degradation of Backfill

No

No change.

SO-C

W77

Solute Transport

No

No change.

UP

W78

Colloid Transport

No

No change.

UP

W79

Colloid Formation and Stability

No

No change.

UP

W80

Colloid Filtration

No

No change.

UP

W81

Colloid Sorption

No

No change.

UP

W82

Suspensions of Particles

No

No change.

DP

W83

Rinse

No

No change.

SO-C

W84

Cuttings

No

No change.

DP

W85

Cavings

No

No change.

DP

W86

Spallings

No

No change.

DP

W87

Microbial Transport

No

No change.

UP

W88

Biofilms

No

No change.

SO-C Beneficial

W89

Transport of Radioactive Gases

No

Screening argument updated with CRA-2009 inventory data.

SO-C

W90

Advection

No

No change.

UP

W91

Diffusion

No

No change.

UP

W92

Matrix Diffusion

No

No change.

UP

W93

Soret Effect

No

New thermal values added for aluminum corrosion.

SO-C

W94

Electrochemical Effects

No

No change.

SO-C

W95

Galvanic Coupling (Outside the Repository)

No

No change.

SO-P

W96

Electrophoresis

No

No change.

SO-C

 

a N = Natural FEP

b H = Human-induced EP

c W = Waste- and Repository-induced FEP

 


Table SCR-2.  FEPs Reassessment Results (Continued)

EPA FEP I.D.a,b,c

FEP Name

Screening Decision Changed

Change Summary

Screening Classification

W97

Chemical Gradients

No

No change.

SO-C

W98

Osmotic Processes

No

No change.

SO-C

W99

Alpha Recoil

No

No change.

SO-C

W100

Enhanced Diffusion

No

No change.

SO-C

W101

Plant Uptake

No

No change.

SO-R (for section 191.13)
SO-C (for section 191.15)

W102

Animal Uptake

No

No change.

SO-R (for section 191.13)
SO-C (for section 191.15)

W103

Accumulation in Soils

No

No change.

SO-C Beneficial (for section 191.13)
SO-C (for section 191.15)

W104

Ingestion

No

No change.

SO-R
SO-C (for section 191.15)

W105

Inhalation

No

No change.

SO-R
SO-C (for section 191.15)

W106

Irradiation

No

No change.

SO-R
SO-C (for section 191.15)

W107

Dermal Sorption

No

No change.

SO-R
SO-C (for section 191.15)

W108

Injection

No

No change.

SO-R
SO-C (for section 191.15)

 

a N = Natural FEP

b H = Human-induced EP

c W = Waste- and Repository-induced FEP

 


This section presents the screening arguments and decisions for natural FEPs.  Natural FEPs may be important to the performance of the disposal system.  Screening of natural FEPs is done in the absence of human influences on the FEPs.  Of the 70 natural FEPs, 68 remain completely unchanged, one has had errors corrected in the screening argument, and one has been updated to include additional information.  No screening decisions (classifications) for natural FEPs were changed, and no additional natural FEPs have been identified.

The Stratigraphy of the geological formations in the region of the WIPP is accounted for in PA calculations.  The presence of Brine Reservoirs in the Castile Formation (hereafter referred to as the Castile) is accounted for in PA calculations.

No new information has been identified for this FEP since the CRA-2004.

The stratigraphy and geology of the region around the WIPP, including the distribution and characteristics of pressurized brine reservoirs in the Castile, are discussed in detail in the CCA, Chapter 2.0, Section 2.1.3.  The stratigraphy of the geological formations in the region of the WIPP is accounted for in PA calculations through the setup of the model geometries (Appendix PA-2009, Section PA-4.2.1).  The presence of brine reservoirs is accounted for in the treatment of inadvertent drilling (Appendix PA-2009, Section PA-4.2.10).

The effects of Regional Tectonics, Regional Uplift and Subsidence, and Change in Regional Stress have been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.

No new information has been identified for this FEP since the CRA-2004.

Regional tectonics encompasses two related issues of concern: the overall level of regional stress and whether any significant changes in regional stress might occur.

The tectonic setting and structural features of the area around the WIPP are described in the CCA, Chapter 2.0, Section 2.1.5.  In summary, there is no geological evidence for Quaternary regional tectonics in the Delaware Basin.  The eastward tilting of the region has been dated as mid-Miocene to Pliocene by King (1948, pp. 120-21) and is associated with the uplift of the Guadalupe Mountains to the west.  Fault zones along the eastern margin of the basin, where it flanks the Central Basin Platform, were active during the Late Permian.  Evidence for this includes the displacement of the Rustler Formation (hereafter referred to as the Rustler) observed by Holt and Powers (1988, pp. 4-14) and the thinning of the Dewey Lake Redbeds Formation (hereafter referred to as the Dewey Lake) reported by Schiel (1994).  There is, however, no surface displacement along the trend of these fault zones, indicating that there has been no significant Quaternary movement.  Other faults identified within the evaporite sequence of the Delaware Basin are inferred by Barrows’ figures in Borns et al. (1983, pp. 58-60) to be the result of salt deformation rather than regional tectonic processes.  According to Muehlberger, Belcher, and Goetz (1978, p. 338), the nearest faults on which Quaternary movement has been identified lie to the west of the Guadalupe Mountains and are of minor regional significance.  The effects of regional tectonics and changes in regional stress have therefore been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.

There are no reported stress measurements from the Delaware Basin, but a low–level, regional stress regime with low deviatoric stress has been inferred from the geological setting of the area (see the CCA, Chapter 2.0, Section 2.1.5).  The inferred low level of regional stress and the lack of Quaternary tectonic activity indicate that regional tectonics and any changes in regional stress will be minor and therefore of low consequence to the performance of the disposal system.  Even if rates of regional tectonic movement experienced over the past 10 million years continue, the extent of regional uplift and subsidence over the next 10,000 years would only be about several feet (ft) (approximately 1 meter [m]).  This amount of uplift or subsidence would not lead to a breach of the Salado because the salt would deform plastically to accommodate this slow rate of movement.  Uniform regional uplift or a small increase in regional dip consistent with this past rate could give rise to downcutting by rivers and streams in the region.  The extent of this downcutting would be little more than the extent of uplift, and reducing the overburden by 1 or 2 m would have no significant effect on groundwater flow or contaminant transport in units above or below the Salado.  Thus the effects of regional uplift and subsidence have been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.

The DOE has screened out, on the basis of either probability or consequence or both, all tectonic, magmatic, and structural processes.  The screening discussions can be found in the CCA, Appendix SCR.  The information needed for this screening is included here and covers (1) regional tectonic processes such as subsidence, uplift, and basin tilting; (2) magmatic processes such as igneous intrusion and events such as volcanism; and (3) structural processes such as faulting and loading and unloading of the rocks because of long-term sedimentation or erosion.  Discussions of structural events, such as earthquakes, are considered to the extent that they may create new faults or activate old faults.  The seismicity of the area is considered in the CCA, Chapter 2.0, Section 2.6 for the purposes of determining seismic design parameters for the facility.

The processes and features included in this section are those more traditionally considered part of tectonics–processes that develop the broad-scale features of the earth.  Salt dissolution is a different process that can develop some features resembling those of tectonics.

Most broad-scale structural elements of the area around the WIPP developed during the Late Paleozoic (see the CCA, Appendix GCR, pp. 3-58 through 3-77).  There is little historical or geological evidence of significant tectonic activity in the vicinity, and the level of stress in the region is low.  The entire region tilted slightly during the Tertiary, and activity related to Basin and Range tectonics formed major structures southwest of the area.  Seismic activity is specifically addressed in a separate section.

Broad subsidence began in the area as early as the Ordovician, developing a sag called the Tobosa Basin.  By Late Pennsylvanian to Early Permian time, the Central Basin Platform developed (see the CCA, Chapter 2.0, Figure 2-19), separating the Tobosa Basin into two parts:  the Delaware Basin to the west and the Midland Basin to the east.  The Permian Basin refers to the collective set of depositional basins in the area during the Permian Period.  Southwest of the Delaware Basin, the Diablo Platform began developing either in the Late Pennsylvanian or Early Permian.  The Marathon Uplift and Ouachita tectonic belt limited the southern extent of the Delaware Basin.

According to Brokaw et al. (1972, p. 30), pre-Ochoan sedimentary rocks in the Delaware Basin show evidence of gentle downwarping during deposition, while Ochoan and younger rocks do not.  A relatively uniform eastward tilt, generally from about 14 to 19 meters per kilometer (m/km) (75 to 100 feet per mile [ft/mi]), has been superimposed on the sedimentary sequence.  King (1948, pp. 108 and 121) generally attributes the uplift of the Guadalupe and Delaware mountains along the west side of the Delaware Basin to the later Cenozoic, though he also notes that some faults along the west margin of the Guadalupe Mountains have displaced Quaternary gravels.

King (1948, p. 144) also infers the uplift from the Pliocene-age deposits of the Llano Estacado.  Subsequent studies of the Ogallala of the Llano Estacado show that it varies in age from Miocene (about 12 million years before present) to Pliocene (Hawley 1993).  This is the most likely range for uplift of the Guadalupe Mountains and broad tilting to the east of the Delaware Basin sequence.

Analysis of the present regional stress field indicates that the Delaware Basin lies within the Southern Great Plains stress province.  This province is a transition zone between the extensional stress regime to the west and the region of compressive stress to the east.  An interpretation by Zoback and Zoback (1991, p. 350) of the available data indicates that the level of stress in the Southern Great Plains stress province is low.  Changes to the tectonic setting, such as the development of subduction zones and a consequent change in the driving forces, would take much longer than 10,000 years to occur.

To the west of the Southern Great Plains province is the Basin and Range province, or Cordilleran Extension province, where according to Zoback and Zoback (1991, pp. 348–51) normal faulting is the characteristic style of deformation.  The eastern boundary of the Basin and Range province is marked by the Rio Grande Rift.  Sanford, Jakasha, and Cash (1991, p. 230) note that, as a geological structure, the Rift extends beyond the relatively narrow geomorphological feature seen at the surface, with a magnetic anomaly at least 500 km (300 mi) wide.  On this basis, the Rio Grande Rift can be regarded as a system of axial grabens along a major north-south trending structural uplift (a continuation of the Southern Rocky Mountains).  The magnetic anomaly extends beneath the Southern Great Plains stress province, and regional-scale uplift of about 1,000 m (3,300 ft) over the past 10 million years also extends into eastern New Mexico.

To the east of the Southern Great Plains province is the large Mid-Plate province that encompasses central and eastern regions of the conterminous United States and the Atlantic basin west of the Mid-Atlantic Ridge.  The Mid-Plate province is characterized by low levels of paleo- and historic seismicity.  Where Quaternary faulting has occurred, it is generally strike-slip and appears to be associated with the reactivation of older structural elements.

Zoback et al. (1991) report no stress measurements from the Delaware Basin.  The stress field in the Southern Great Plains stress province has been defined from borehole measurements in west Texas and from volcanic lineaments in northern New Mexico.  These measurements were interpreted by Zoback and Zoback (1991, p. 353) to indicate that the least principal horizontal stress is oriented north-northeast and south-southwest and that most of the province is characterized by an extensional stress regime.

There is an abrupt change between the orientation of the least principal horizontal stress in the Southern Great Plains and the west-northwest orientation of the least principal horizontal stress characteristic of the Rio Grande Rift.  In addition to the geological indications of a transition zone as described above, Zoback and Zoback (1980, p. 6134) point out that there is also evidence for a sharp boundary between these two provinces.  This is reinforced by the change in crustal thickness from about 40 km (24 mi) beneath the Colorado Plateau to about 50 km (30 mi) or more beneath the Southern Great Plains east of the Rio Grande Rift.  The base of the crust within the Rio Grande Rift is poorly defined but is shallower than that of the Colorado Plateau (Thompson and Zoback 1979, p. 152). There is also markedly lower heat flow in the Southern Great Plains (typically < 60 m W m-2) reported by Blackwell, Steele, and Carter (1991, p. 428) compared with that in the Rio Grande Rift (typically > 80 m W m-2) reported by Reiter, Barroll, and Minier (1991, p. 463).

On the eastern boundary of the Southern Great Plains province, there is only a small rotation in the direction of the least principal horizontal stress.  There is, however, a change from an extensional, normal faulting regime to a compressive, strike-slip faulting regime in the Mid-Plate province.  According to Zoback and Zoback (1980, p. 6134), the available data indicate that this change is not abrupt and that the Southern Great Plains province can be viewed as a marginal part of the Mid-Plate province.

Natural Salt Deformation and Diapirism at the WIPP site over the next 10,000 yrs on a scale severe enough to significantly affect performance of the disposal system have been eliminated from PA calculations on the basis of low probability of occurrence.

No new information has been identified for this FEP since the CRA-2004.

SCR-4.1.3.1.1.3.1  Deformation

Some of the evaporites in the northern Delaware Basin have been deformed and it has been proposed that the likely mechanism for deformation is gravity foundering of the more dense anhydrites in less dense halite (e.g., Anderson and Powers 1978, Jones 1981, Borns et al. 1983, and Borns 1987). Diapirism occurs when the deformation is penetrative, i.e., halite beds disrupt overlying anhydrites. As Anderson and Powers (1978) suggested, this may have happened northeast of the WIPP at the location of drillhole ERDA-6. This is the only location where diapirism has been suggested for the evaporites of the northern Delaware Basin. The geologic situation suggests that deformation occurred before the Miocene-Pliocene Ogallala Formation was deposited (Jones 1981). Mechanical modeling is consistent with salt deformation occurring over about 700,000 yrs to form the deformed features known in the northern part of the WIPP site (Borns et al. 1983). The DOE drew the conclusion that evaporites at the WIPP site deform too slowly to affect performance of the disposal system.

Because brine reservoirs appear to be associated with deformation, Powers et al. (1996) prepared detailed structure elevation maps of various units from the base of the Castile upward through the evaporites in the northern Delaware Basin.  Drillholes are far more numerous for this study than at the time of the study by Anderson and Powers (1978). Subdivisions of the Castile appear to be continuous in the vicinity of ERDA-6 and at ERDA-6. There is little justification for interpreting diapiric piercement at that site.  The location and distribution of evaporite deformation in the area of the WIPP site is similar to that proposed by earlier studies (e.g., Anderson and Powers 1978, Borns et al. 1983, Borns and Shaffer 1985).

Surface domal features at the northwestern end of Nash Draw were of undetermined origin prior to WIPP investigations (e.g., Vine 1963), but extensive geophysical studies were conducted of these features as part of early WIPP studies (see Powers 1996).  Two of the domal features were drilled, demonstrating that they had a solution-collapse origin (breccia pipes) and were not related in any way to salt diapirism (Snyder and Gard 1982).

A more recent study of structure for the Culebra Dolomite Member of the Rustler Formation (hereafter referred to as the Culebra) (Powers 2003) shows that the larger deformation associated with deeper units is reflected by the Culebra, although the structural relief is muted. In addition, evaporite deformation in the northern part of the WIPP site, associated with the area earlier termed the “disturbed zone” (Powers et al. 1978), is hardly observable on a map of Culebra structure (Powers 2003). There is no evidence of more recent deformation at the WIPP site based on such maps.

Deformed salt in the lower Salado and upper strata of the Castile has been encountered in a number of boreholes around the WIPP site; the extent of existing salt deformation is summarized in the CCA, Chapter 2.0, Section 2.1.6.1, and further detail is provided in the CCA, Appendix DEF.

A number of mechanisms may result in salt deformation: in massive salt deposits, buoyancy effects or diapirism may cause salt to rise through denser, overlying units; and in bedded salt with anhydrite or other interbeds, gravity foundering of the interbeds into the halite may take place.  Results from rock mechanics modeling studies (see the CCA, Appendix DEF) indicate that the time scale for the deformation process is such that significant natural deformation is unlikely to occur at the WIPP site over any time frame significant to waste isolation.  Thus natural salt deformation and diapirism severe enough to alter existing patterns of groundwater flow or the behavior of the disposal system over the regulatory period has been eliminated from PA calculations on the basis of low probability of occurrence over the next 10,000 yrs.

Formation of Fractures has been eliminated from PA calculations on the basis of a low probability of occurrence over 10,000 yrs.  The Formation of Fractures near the repository is accounted for in PA through treatment of the DRZ.

No new information has been identified for this FEP since the CRA-2004.

The formation of fractures requires larger changes in stress than are required for changes to the properties of existing fractures to overcome the shear and tensile strength of the rock.  It has been concluded from the regional tectonic setting of the Delaware Basin that no significant changes in regional stress are expected over the regulatory period.  The EPA agrees that fracture formation in the Rustler is likely a result of halite dissolution and subsequent overlying unit fracturing loading/unloading, as well as the syn- and postdepositional processes.  Intraformational postdepositional dissolution of the Rustler has been ruled out as a major contributor to Rustler salt distribution and thus to new fracture formation based on work by Holt and Powers in the CCA (Appendix DEF, Section DEF3.2) and Powers and Holt (1999 and 2000), who believe that depositional facies and syndepositional dissolution account for most of the patterns on halite distribution in the Rustler.  The argument against developing new fractures in the Rustler during the regulatory period appears reasonable.  The formation of new fracture sets in the Culebra has therefore been eliminated from PA calculations on the basis of a low probability of occurrence over 10,000 yrs.

Repository-induced fracturing of the DRZ and Salado interbeds is accounted for in PA calculations.

A mechanism such as salt diapirism could develop fracturing in the Salado, but there is little evidence of diapirism in the Delaware Basin.  Salt deformation has occurred in the vicinity of the WIPP, and fractures have developed in deeper Castile anhydrites as a consequence. Deformation rates are slow, and it is highly unlikely that this process will induce significant new fractures in the Salado during the regulatory time period.  Surface domal features at the northwestern end of Nash Draw were of undetermined origin prior to WIPP investigations (e.g., Vine 1963), but extensive geophysical studies were conducted of these features as part of early WIPP studies (see Powers 1996). Two of the domal features were drilled, demonstrating that they had a solution-collapse origin (breccia pipes) and were not related in any way to salt diapirism (Snyder and Gard 1982).

Naturally induced Changes in Fracture Properties that may affect groundwater flow or radionuclide transport in the region of the WIPP have been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.  Changes in Fracture Properties near the repository are accounted for in PA calculations through treatment of the DRZ.

No new information has been identified for this FEP since the CRA-2004.

Groundwater flow in the region of the WIPP and transport of any released radionuclides may take place along fractures.  The rate of flow and the extent of transport will be influenced by fracture characteristics.  Changes in fracture properties could arise through natural changes in the local stress field; for example, through tectonic processes, erosion or sedimentation changing the amount of overburden, dissolution of soluble minerals along beds in the Rustler or upper Salado, or dissolution or precipitation of minerals in fractures.

Tectonic processes and features (changes in regional stress [N3]; tectonics [N4]; regional uplift and subsidence [N5]; salt deformation [N6]; diapirism [N7]) have been screened out of PA. These processes are not expected to significantly change the character of fractures during the regulatory period.

Surface erosion or deposition (e.g., N41–N49) are not expected to significantly change the overburden on the Culebra during the regulatory period. The relationship between Culebra transmissivity and depth is significant (Holt and Yarbrough 2002, Holt and Powers 2002), but the potential change to Culebra transmissivity based on deposition or erosion from these processes over the regulatory period is insignificant.

Shallow dissolution (N16), where soluble beds from the upper Salado or Rustler are removed by groundwater, has been extensively considered. There are no direct effects on the Salado at depths of the repository. Extensive study of the upper Salado and Rustler halite units (Holt and Powers 1988, the CCA, Appendix FAC, Powers and Holt 1999 and 2000, Powers 2003) indicates little potential for dissolution at the WIPP site during the regulatory period. Existing fracture properties are expressed through the relationship between Culebra transmissivity values and geologic factors at and near the WIPP site (Holt and Yarbrough 2002; Holt and Powers 2002, p. 215). These will be incorporated in PA (see N16, Shallow Dissolution).

Mineral precipitation within fractures (N22) is expected to be beneficial to performance, and it has been screened out on the basis of low consequence.  Natural dissolution of fracture fillings within the Culebra is incorporated within FEP N16 (Shallow Dissolution).  There is no new information on the distribution of fracture fillings within the Culebra.  The effects of fracture fillings are also expected to be represented in the distribution of Culebra transmissivity values around the WIPP site and are thus incorporated into PA.

Repository-induced fracturing of the DRZ and Salado interbeds is accounted for in PA calculations (UP), and is discussed further in FEPs W18 and W19.

Naturally induced Fault Movement and Formation of New Faults of sufficient magnitude to significantly affect the performance of the disposal system have been eliminated from PA calculations on the basis of low probability of occurrence over 10,000 yrs.

No changes have been made to this FEP.

Faults are present in the Delaware Basin in both the units underlying the Salado and in the Permian evaporite sequence (see the CCA, Section 2.1.5.3).  According to Powers et al. (1978 included in the CCA, Appendix GCR), there is evidence that movement along faults within the pre-Permian units affected the thickness of Early Permian strata, but these faults did not exert a structural control on the deposition of the Castile, the Salado, or the Rustler.  Fault zones along the margins of the Delaware Basin were active during the Late Permian Period.  Along the eastern margin, where the Delaware Basin flanks the Central Basin Platform, Holt and Powers (1988, also included in the CCA, Appendix FAC) note that there is displacement of the Rustler, and Schiel (1994) notes that there is thinning of the Dewey Lake.  There is, however, no surface displacement along the trend of these fault zones, indicating that there has been no significant Quaternary movement. Muehlberger et al. (1978, p. 338) note that the nearest faults on which Quaternary movement has been identified lie to the west of the Guadalupe Mountains.

The WIPP is located in an area of tectonic quiescence. Seismic monitoring conducted for the WIPP since the CCA continues to record small events at distance from the WIPP, and these events are mainly in areas associated with hydrocarbon production.  Two nearby events (magnitude 3.5, October 1997, and magnitude 2.8, December 1998) are related to rockfalls in the Nash Draw mine and are not tectonic in origin (U.S. Department of Energy 1999). These events did not cause any damage at the WIPP. The absence of Quaternary fault scarps and the general tectonic setting and understanding of its evolution indicate that large-scale, tectonically induced fault movement within the Delaware Basin can be eliminated from PA calculations on the basis of low probability over 10,000 yrs.  The stable tectonic setting also allows the formation of new faults within the basin over the next 10,000 yrs to be eliminated from PA calculations on the basis of low probability of occurrence.

Evaporite dissolution at or near the WIPP site has the potential for developing fractures in the overlying beds. Three zones with halite (top of Salado, M1/H1 of the Los Medaños Member, and M2/H2 of the Los Medaños Member) underlie the Culebra at the site (Powers 2003). The upper Salado is present across the site, and there is no indication that dissolution of this area will occur in the regulatory period or cause faulting at the site. The Los Medaños units show both mudflat facies and halite-bearing facies within or adjacent to the WIPP site (Powers 2003). Although the distribution of halite in the Rustler is mainly the result of depositional facies and syndepositional dissolution (Holt and Powers 1988, Powers and Holt 1999 and 2000), the possibility of past or future halite dissolution along the margins cannot be ruled out (Holt and Powers 1988, Beauheim and Holt 1999). If halite in the lower Rustler has been dissolved along the depositional margin, it has not occurred recently or has been of no consequence, as there is no indication on the surface or in Rustler structure of new (or old) faults in this area (e.g., Powers et al. 1978, Powers 2003).

The absence of Quaternary fault scarps and the general tectonic setting and understanding of its evolution indicate that large-scale, tectonically induced fault movement within the Delaware Basin can be eliminated from PA calculations on the basis of low probability over 10,000 years.  The stable tectonic setting also allows the formation of new faults within the basin over the next 10,000 years to be eliminated from PA calculations on the basis of low probability of occurrence.

The postclosure effects of Seismic Activity on the repository and the DRZ are accounted for in PA calculations.

Seismic monitoring conducted for the WIPP since the CRA-2004 continues to record small events at a distance from the WIPP, mainly in areas associated with hydrocarbon production.  Three seismic events (magnitude 2.4, January 27, 2006; magnitude 3.8, December 19, 2005; and magnitude 3.6, May 23, 2004) occurred within 300 km of the WIPP (see U.S. Department of Energy 2005, 2006, 2007a).  These events did not cause any damage at the WIPP.

The following subsections present the screening argument for seismic activity (groundshaking).

Seismic activity describes transient ground motion that may be generated by several energy sources.  There are two possible causes of seismic activity that could potentially affect the WIPP site:  natural and human-induced.  Natural seismic activity is caused by fault movement (earthquakes) when the buildup of strain in rock is released through sudden rupture or movement.  Human-induced seismic activity may result from a variety of surface and subsurface activities, such as explosions (H19 and H20), mining (H13, H14, H58, and H59), fluid injection (H28), and fluid withdrawal (H25).

Ground vibration and the consequent shaking of buildings and other structures are the most obvious effects of seismic activity.  Once the repository and shafts have been sealed, however, existing surface structures will be dismantled.  Postclosure PAs are concerned with the effects of seismic activity on the closed repository.

In regions of low and moderate seismic activity, such as the Delaware Basin, rocks behave elastically in response to the passage of seismic waves, and there are no long-term changes in rock properties.  The effects of earthquakes beyond the DRZ have been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.  An inelastic response, such as cracking, is only possible where there are free surfaces, as in the roof and walls of the repository prior to closure by creep.  Seismic activity could, therefore, have an effect on the properties of the DRZ.

An assessment of the extent of damage in underground excavations caused by groundshaking depends largely on observations from mines and tunnels.  Because such excavations tend to take place in rock types more brittle than halite, these observations cannot be related directly to the behavior of the WIPP.  According to Wallner (1981, p. 244), the DRZ in brittle rock types is likely to be more highly fractured and hence more prone to spalling and rockfalls than an equivalent zone in salt.  Relationships between groundshaking and subsequent damage observed in mines will therefore be conservative with respect to the extent of damage induced at the WIPP by seismic activity.

Dowding and Rozen (1978) classified damage in underground structures following seismic activity and found that no damage (cracks, spalling, or rockfalls) occurred at accelerations below 0.2 gravities and that only minor damage occurred at accelerations up to 0.4 gravities.  Lenhardt (1988, p. 392) showed that a magnitude 3 earthquake would have to be within 1 km (0.6 mi) of a mine to result in falls of loose rock.  The risk of seismic activity in the region of the WIPP reaching these thresholds is discussed below.

Prior to the introduction of a seismic monitoring network in 1960, most recorded earthquakes in New Mexico were associated with the Rio Grande Rift, although small earthquakes were detected in other parts of the region.  In addition to continued activity in the Rio Grande Rift, the instrumental record has shown a significant amount of seismic activity originating from the Central Basin Platform and a number of small earthquakes in the Los Medaños area.  Seismic activity in the Rio Grande Rift is associated with extensional tectonics in that area.  Seismic activity in the Central Basin Platform may be associated with natural earthquakes, but there are also indications that this activity occurs in association with oil-field activities such as fluid injection.  Small earthquakes in the Los Medaños region have not been precisely located, but may be the result of mining activity in the region.  The CCA, Chapter 2.0, Section 2.6.2 contains additional discussion of seismic activity and risk in the WIPP region.

The instrumental record was used as the basis of a seismic risk study primarily intended for design calculations of surface facilities rather than for postclosure PAs.  The use of this study to define probable ground accelerations in the WIPP region over the next 10,000 yrs is based on the assumptions that hydrocarbon extraction and potash mining will continue in the region and that the regional tectonic setting precludes major changes over the next 10,000 yrs.

Three source regions were used in calculating seismic risk: the Rio Grande Rift, the Central Basin Platform, and part of the Delaware Basin province (including the Los Medaños).  Using conservative assumptions about the maximum magnitude event in each zone, the study indicated a return period of about 10,000 years (annual probability of occurrence of 10-4) for events producing ground accelerations of 0.1 gravities.  Ground accelerations of 0.2 gravities would have an annual probability of occurrence of about 5 × 10-6.

The results of the seismic risk study and the observations of damage in mines caused by groundshaking give an estimated annual probability of occurrence of between 10-8 and 10-6 for events that could increase the permeability of the DRZ.  The DRZ is accounted for in PA calculations as a zone of permanently high permeability (see Appendix PA-2009, Section PA-4.2.4); this treatment is considered to account for the effects of any potential seismic activity.

Volcanic Activity has been eliminated from PA calculations on the basis of low probability of occurrence over 10,000 yrs.

No new information has been identified for this FEP since the CRA-2004.

The Paleozoic and younger stratigraphic sequences within the Delaware Basin are devoid of locally derived volcanic rocks.  Volcanic ashes (dated at 13 million years and 0.6 million years) do occur in the Gatuña Formation (hereafter referred to as the Gatuña), but these are not locally derived.  Within eastern New Mexico and northern, central, and western Texas, the closest Tertiary volcanic rocks with notable areal extent or tectonic significance to the WIPP are approximately 160 km (100 mi) to the south in the Davis Mountains volcanic area.  The closest Quaternary volcanic rocks are 250 km (150 mi) to the northwest in the Sacramento Mountains.  No volcanic rocks are exposed at the surface within the Delaware Basin.

Volcanic activity is associated with particular tectonic settings: constructive and destructive plate margins, regions of intraplate rifting, and isolated hot-spots in intraplate regions.  The tectonic setting of the WIPP site and the Delaware Basin is remote from plate margins, and the absence of past volcanic activity indicates the absence of a major hot spot in the region.  Intraplate rifting has taken place along the Rio Grande some 200 km (120 mi) west of the WIPP site during the Tertiary and Quaternary Periods.  Igneous activity along this rift valley is comprised of sheet lavas intruded on by a host of small-to-large plugs, sills, and other intrusive bodies.  However, the geological setting of the WIPP site within the large and stable Delaware Basin allows volcanic activity in the region of the WIPP repository to be eliminated from performance calculations on the basis of low probability of occurrence over the next 10,000 years.

The effects of Magmatic Activity have been eliminated from the PA calculations on the basis of low consequence to the performance of the disposal system.

No new information has been identified for this FEP.

Magmatic activity is defined as the subsurface intrusion of igneous rocks into country rock.  Deep intrusive igneous rocks crystallize at depths of several kilometers (several miles) and have no surface or near-surface expression until considerable erosion has taken place.  Alternatively, intrusive rocks may form from magma that has risen to near the surface or in the vents that give rise to volcanoes and lava flows.  Magma near the surface may be intruded along subvertical and subhorizontal discontinuities (forming dikes and sills, respectively), and magma in volcanic vents may solidify as plugs.  The formation of such features close to a repository or the existence of a recently intruded rock mass could impose thermal stresses, inducing new fractures or altering the hydraulic characteristics of existing fractures.

The principal area of magmatic activity in New Mexico is the Rio Grande Rift, where extensive intrusions occurred during the Tertiary and Quaternary Periods.  The Rio Grande Rift, however, is in a different tectonic province than the Delaware Basin, and its magmatic activity is related to the extensional stress regime and high heat flow in that region.

Within the Delaware Basin, there is a single identified outcrop of a lamprophyre dike about 70 km (40 mi) southwest of the WIPP (see the CCA, Chapter 2.0, Section 2.1.5.4 and the CCA, Appendix GCR for more detail).  Closer to the WIPP site, similar rocks have been exposed within potash mines some 15 km (10 mi) to the northwest, and igneous rocks have been reported from petroleum exploration boreholes.  Material from the subsurface exposures has been dated at around 35 million years.  Some recrystallization of the host rocks took place alongside the intrusion, and there is evidence that minor fracture development and fluid migration also occurred along the margins of the intrusion.  However, the fractures have been sealed, and there is no evidence that the dike acted as a conduit for continued fluid flow.

Aeromagnetic surveys of the Delaware Basin have shown anomalies that lie on a linear southwest-northeast trend that coincides with the surface and subsurface exposures of magmatic rocks.  There is a strong indication, therefore, of a dike or a closely related set of dikes extending for at least 120 km (70 mi) across the region (see the CCA, Chapter 2.0, Section 2.1.5.4).  The aeromagnetic survey conducted to delineate the dike showed a magnetic anomaly that is several kilometers (several miles) wide at depth and narrows to a thin trace near the surface.  This pattern is interpreted as the result of an extensive dike swarm at depths of less than approximately 4.0 km (2.5 mi) near the Precambrian basement, from which a limited number of dikes have extended towards the surface.

Magmatic activity has taken place in the vicinity of the WIPP site in the past, but the igneous rocks have cooled over a long period.  Any enhanced fracturing or conduits for fluid flow have been sealed by salt creep and mineralization.  Continuing magmatic activity in the Rio Grande Rift is too remote from the WIPP location to be of consequence to the performance of the disposal system.  Thus the effects of magmatic activity have been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.

Metamorphic Activity has been eliminated from PA calculations on the basis of low probability of occurrence over the next 10,000 years.

No new information has been identified for this FEP since the CRA-2004.

Metamorphic activity, that is, solid-state recrystallization changes to rock properties and geologic structures through the effects of heat and/or pressure, requires depths of burial much greater than the depth of the repository.  Regional tectonics that would result in the burial of the repository to the depths at which the repository would be affected by metamorphic activity have been eliminated from PA calculations on the basis of low probability of occurrence; therefore, metamorphic activity has also been eliminated from PA calculations on the basis of low probability of occurrence over the next 10,000 years.

Shallow Dissolution is accounted for in PA calculations.

No new information has been identified for this FEP since the CRA-2004.

This section discusses a variety of styles of dissolution that have been active in the region of the WIPP or in the Delaware Basin.  A distinction has been drawn between shallow dissolution involving circulation of groundwater, mineral dissolution in the Rustler and at the top of the Salado in the region of the WIPP, and deep dissolution taking place in the Castile and the base of the Salado.  Dissolution will initially enhance porosities, but continued dissolution may lead to compaction of the affected units with a consequent reduction in porosity.  Compaction may result in fracturing of overlying brittle units and increased permeability.  Extensive dissolution may create cavities (karst) and result in the total collapse of overlying units.  This topic is discussed further in the CCA, Chapter 2.0, Section 2.1.6.2.

In the region around the WIPP, shallow dissolution by groundwater flow has removed soluble minerals from the upper Salado as well as the Rustler to form Nash Draw; extensive solution within the closed draw has created karst features including caves and dolines in the sulfate beds of the Rustler (see Lee, 1925, Bachman, 1980, 1985, and 1987a). An alluvial doline drilled at WIPP 33, about 850 m (2800 ft) west of the WIPP site boundary, is the nearest karst feature known in the vicinity of the site. Upper Salado halite dissolution in Nash Draw resulted in fracture propagation upward through the overlying Rustler (Holt and Powers 1988). The margin of dissolution of halite from the upper Salado has commonly been placed west of the WIPP site, near, but east of, Livingston Ridge, the eastern boundary of Nash Draw. Halite occurs in the Rustler east of Livingston Ridge, with the margin generally progressively eastward in higher stratigraphic units (e.g., Snyder 1985; Powers and Holt 1995). The distribution of halite in the Rustler has commonly been attributed to shallow dissolution (e.g., Powers et al. 1978; Lambert, 1983; Bachman 1985; Lowenstein 1987). During early studies for the WIPP, the variability of Culebra transmissivity in the vicinity of the WIPP was commonly attributed to the effects of Rustler halite dissolution and changes in fracturing as a consequence.

After a detailed sedimentologic and stratigraphic investigation of WIPP cores, shafts, and geophysical logs from the region around WIPP, the distribution of halite in the Rustler was attributed to depositional and syndepositional processes rather than postdepositional dissolution (Holt and Powers 1988; Powers and Holt 2000).  Rustler exposures in shafts for the WIPP revealed extensive sedimentary structures in clastic units (Holt and Powers 1984, 1986, 1990), and the suite of features in these beds led these investigators (Holt and Powers 1988; Powers and Holt 1990, 2000) to reinterpret the clastic units. They conclude that the clastic facies represent mainly mudflat facies tracts adjacent to a salt pan. Although some halite was likely deposited in mudflat areas proximal to the salt pan, it was largely removed by syndepositional dissolution, as indicated by soil structures, soft sediment deformation, bedding, and small-scale vertical relationships (Holt and Powers 1988; Powers and Holt 1990, 1999, 2000). The depositional margins of halite in the Rustler are the likely points for past or future dissolution (e.g., Holt and Powers 1988; Beauheim and Holt 1990). Cores from drillholes at the H-19 drillpad near the Tamarisk Member halite margin show evidence of some dissolution of halite in the Tamarisk (Mercer et al. 1998), consistent with these predictions. The distribution of Culebra transmissivity values is not considered related to dissolution of Rustler halite, and other geological factors (e.g., depth, upper Salado dissolution) correlate well with Culebra transmissivity (e.g., Powers and Holt 1995; Holt and Powers 2002).

Since the CCA was completed, the WIPP has conducted additional work on shallow dissolution, principally of the upper Salado, and its possible relationship to the distribution of transmissivity values for the Culebra as determined through testing of WIPP hydrology wells.

Analysis Plan 088 (AP-088) (Beauheim 2002) noted that potentiometric surface values for the Culebra in many monitoring wells were outside the uncertainty ranges used to calibrate models of steady-state heads for the unit. AP-088 directed the analysis of the relationship between geological factors and values of transmissivity at Culebra wells. The relationship between geological factors, including dissolution of the upper Salado as well as limited dissolution in the Rustler, and Culebra transmissivity is being used to evaluate differences between assuming steady-state Culebra heads and changing heads.

Task 1 for AP-088 (Powers 2003) evaluated geological factors, including shallow dissolution in the vicinity of the WIPP site related to Culebra transmissivity. A much more extensive drillhole geological database was developed than was previously available, utilizing sources of data from WIPP, potash exploration, and oil and gas exploration and development. The principal findings related to shallow dissolution are (1) a relatively narrow zone (~ 200 – 400 m [656 – 1,312 ft] wide) could be defined as the margin of dissolution of the upper Salado in much of the area around WIPP, (2) the upper Salado dissolution margin commonly underlies surface escarpments such as Livingston Ridge, and (3) there are possible extensions or reentrants of incipient upper Salado dissolution extending eastward from the general dissolution margin. The WIPP site proper is not affected by this process.

Culebra transmissivity correlates well with depth or overburden, which affects fracture apertures (Powers and Holt 1995, Holt and Powers 2002; Holt and Yarbrough 2002). Dissolution of the upper Salado appears to increase transmissivity by one or more orders of magnitude (Holt and Yarbrough 2002). Because there is no indication of upper Salado dissolution at the WIPP site, Holt and Yarbrough (2002) did not include this factor for the WIPP site in estimates of base transmissivity values for the WIPP site and surroundings.

The effects of shallow dissolution (including the impacts of lateral dissolution) have been included in PA calculations.

Deep Dissolution and the formation of associated features (for example, solution chimneys or Breccia Pipes, Collapse Breccias) at the WIPP site have been eliminated from PA calculations on the basis of low probability of occurrence over the next 10,000 years.

No new information has been identified for this FEP since the CRA-2004.

This section discusses a variety of styles of dissolution that have been active in the region of the WIPP or in the Delaware Basin.  A distinction has been drawn between shallow dissolution, involving circulation of groundwater and mineral dissolution in the Rustler and at the top of the Salado in the region of the WIPP, and deep dissolution taking place in the Castile and the base of the Salado.  Dissolution will initially enhance porosities, but continued dissolution may lead to compaction of the affected units with a consequent reduction in porosity.  Compaction may result in fracturing of overlying brittle units and increased permeability.  Extensive dissolution may create cavities (karst) and result in the total collapse of overlying units.  This topic is discussed further in the CCA, Chapter 2.0, Section 2.1.6.2.

Deep dissolution is limited to processes involving dissolution of the Castile or basal Salado and features such as breccia pipes (also known as solution chimneys) associated with this process (see the CCA, Chapter 2.0, Section 2.1.6.2).  Deep dissolution is distinguished from shallow and lateral dissolution not only by depth, but also by the origin of the water.  Dissolution by groundwater from deep water-bearing zones can lead to the formation of cavities.  Collapse of overlying beds leads to the formation of collapse breccias if the overlying rocks are brittle, or to deformation if the overlying rocks are ductile.  If dissolution is extensive, breccia pipes or solution chimneys may form above the cavity.  These pipes may reach the surface or pass upwards into fractures and then into microcracks that do not extend to the surface.  Breccia pipes may also form through the downward percolation of meteoric waters, as discussed earlier.  Deep dissolution is of concern because it could accelerate contaminant transport through the creation of vertical flow paths that bypass low-permeability units in the Rustler.  If dissolution occurred within or beneath the waste panels themselves, there could be increased circulation of groundwater through the waste, as well as a breach of the Salado host rock.

Features identified as being the result of deep dissolution are present along the northern and eastern margins of the Delaware Basin.  In addition to features that have a surface expression or that appear within potash mine workings, deep dissolution has been cited by Anderson et al. (1972, p. 81) as the cause of lateral variability within evaporite sequences in the lower Salado.

Exposures of the McNutt Potash Member of the Salado within a mine near Nash Draw have shown a breccia pipe containing cemented brecciated fragments of formations higher in the stratigraphic sequence.  At the surface, this feature is marked by a dome, and similar domes have been interpreted as dissolution features.  The depth of dissolution has not been confirmed, but the collapse structures led Anderson (1978, p. 52) and Snyder et al. (1982, p. 65) to postulate dissolution of the Capitan Limestone at depth; collapse of the Salado, Rustler, and younger formations; and subsequent dissolution and hydration by downward percolating waters.  San Simon Sink (see the CCA, Chapter 2.0, Section 2.1.6.2), some 35 km (20 mi) east-southeast of the WIPP site, has also been interpreted as a solution chimney.  Subsidence has occurred there in historical times according to Nicholson and Clebsch (1961, p. 14), suggesting that dissolution at depth is still taking place.  Whether this is the result of downward-percolating surface water or deep groundwater has not been confirmed.  The association of these dissolution features with the inner margin of the Capitan Reef suggest that they owe their origins, if not their continued development, to groundwaters derived from the Capitan Limestone.

The Castile contains sequences of varved anhydrite and carbonate (that is, laminae deposited on a cyclical basis) that can be correlated between several boreholes.  On the basis of these deposits, a basin-wide uniformity in the depositional environment of the Castile evaporites was assumed.  The absence of varves from all or part of a sequence and the presence of brecciated anhydrite beds have been interpreted by Anderson et al. (1972) as evidence of dissolution.  Holt and Powers (the CCA, Appendix FAC) have questioned the assumption of a uniform depositional environment and contend that the anhydrite beds are lateral equivalents of halite sequences without significant postdepositional dissolution.  Wedges of brecciated anhydrite along the margin of the Castile have been interpreted by Robinson and Powers (1987, p. 78) as gravity-driven clastic deposits, rather than the result of deep dissolution.

Localized depressions at the top of the Castile and inclined geophysical marker units at the base of the Salado have been interpreted by Davies (1983, p. 45) as the result of deep dissolution and subsequent collapse or deformation of overlying rocks.  The postulated cause of this dissolution was circulation of undersaturated groundwaters from the Bell Canyon Formation (hereafter referred to as Bell Canyon).  Additional boreholes (notably WIPP-13, WIPP-32, and DOE-2) and geophysical logging led Borns and Shaffer (1985) to conclude that the features interpreted by Davies as being dissolution features are the result of irregularities at the top of Bell Canyon.  These irregularities led to localized depositional thickening of the Castile and lower Salado sediments.

Collapse breccias are present at several places around the margins of the Delaware Basin.  Their formation is attributed to relatively fresh groundwater from the Capitan Limestone that forms the margin of the basin.  Collapse breccias corresponding to features on geophysical records that have been ascribed to deep dissolution have not been found in boreholes away from the margins.  These features have been reinterpreted as the result of early dissolution prior to the deposition of the Salado.

Deep dissolution features have been identified within the Delaware Basin, but only in marginal areas underlain by Capitan Reef.  There is a low probability that deep dissolution will occur sufficiently close to the waste panels over the regulatory period to affect groundwater flow in the immediate region of the WIPP.  Deep dissolution at the WIPP site has therefore been eliminated from PA calculations on the basis of low probability of occurrence over the next 10,000 years.

The effects of Fracture Infill have been eliminated from PA calculations on the basis of beneficial consequence to the performance of the disposal system.

No new information has been identified for this FEP since the CRA-2004.  No changes have been made.

Precipitation of minerals as fracture infills can reduce hydraulic conductivities.  The distribution of infilled fractures in the Culebra closely parallels the spatial variability of lateral transmissivity in the Culebra.  The secondary gypsum veins in the Rustler have not been dated.  Strontium isotope studies (Siegel et al. 1991, pp. 5-53 to 5-57) indicate that the infilling minerals are locally derived from the host rock rather than extrinsically derived, and it is inferred that they reflect an early phase of mineralization and are not associated with recent meteoric waters.

Stable isotope geochemistry in the Rustler has also provided information on mineral stabilities in these strata.  Both Chapman (1986, p. 31) and Lambert and Harvey (1987, p. 207) imply that the mineralogical characteristics of units above the Salado have been stable or subject to only minor changes under the various recharge conditions that have existed during the past 0.6 million years—the period since the formation of the Mescalero caliche and the establishment of a pattern of climate change and associated changes in recharge that led to present-day hydrogeological conditions.  No changes in climate are expected other than those experienced during this period, and for this reason, no changes are expected in the mineralogical characteristics other than those expressed by the existing variability of fracture infills and diagenetic textures.  Formation of fracture infills will reduce transmissivities and will therefore be of beneficial consequence to the performance of the disposal system.

Saturated Groundwater Flow, Unsaturated Groundwater Flow, Fracture Flow, and Effects of Preferential Pathways are accounted for in PA calculations.

No new information has been identified for these FEPs.  They continue to be accounted for in PA.

Saturated groundwater flow, unsaturated groundwater flow, and fracture flow are accounted for in PA calculations.  Groundwater flow is discussed in the CCA, Chapter 2.0, Section 2.2.1; and Chapter 6.0, Section 6.4.5 and Section 6.4.6.

The hydrogeologic properties of the Culebra are also spatially variable. This variability, including the effects of preferential pathways, is accounted for in PA calculations in the estimates of transmissivity and aquifer thickness.

Density Effects on Groundwater Flow has been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.

No new information has been identified for this FEP since the CRA-2004.

The most transmissive unit in the Rustler, and hence the most significant potential pathway for transport of radionuclides to the accessible environment, is the Culebra.  The properties of Culebra groundwaters are not homogeneous, and spatial variations in groundwater density (the CCA, Chapter 2.0, Section 2.2.1.4.1.2) could influence the rate and direction of groundwater flow.  A comparison of the gravity-driven flow component and the pressure-driven component in the Culebra, however, shows that only in the region to the south of the WIPP are head gradients low enough for density gradients to be significant (Davies 1989, p. 53).  Accounting for this variability would rotate groundwater flow vectors towards the east (down-dip) and hence fluid in the high-transmissivity zone would move away from the zone.  Excluding brine density variations within the Culebra from PA calculations is therefore a conservative assumption, and density effects on groundwater flow have been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.

Natural Thermal Effects on Groundwater Flow have been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.

No new information has been identified for this FEP since the CRA-2004.

The geothermal gradient in the region of the WIPP has been measured at about 30 °C (54 °F) per kilometer (50 °C [90 °F] per mile).  Given the generally low permeability in the region and the limited thickness of units in which groundwater flow occurs (for example, the Culebra), natural convection will be too weak to have a significant effect on groundwater flow.  No natural FEPs have been identified that could significantly alter the temperature distribution of the disposal system or give rise to thermal effects on groundwater flow.  Such effects have therefore been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.

Changes in groundwater flow arising from Saline Intrusion have been eliminated from PA calculations on the basis of low probability of occurrence over 10,000 years.

No new information has been identified for this FEP since the CRA-2004.

No natural events or processes have been identified that could result in saline intrusion into units above the Salado or cause a significant increase in fluid density.  Natural saline intrusion has therefore been eliminated from PA calculations on the basis of low probability of occurrence over the next 10,000 years.  Saline intrusion arising from human events such as drilling into a pressurized brine pocket is discussed in FEPs H21 through H24 (Section SCR-5.2.1.4).

Changes in groundwater flow arising from Freshwater Intrusion have been eliminated from PA calculations on the basis of low probability of occurrence over 10,000 years.

No new information has been identified for this FEP since the CRA-2004.

A number of FEPs, including climate change, can result in changes in infiltration and recharge (see discussions for FEPs N53 through N55, Section SCR-4.5.3.1).  These changes will affect the height of the water table and, hence, could affect groundwater flow in the Rustler through changes in head gradients.  The generally low transmissivity of the Dewey Lake and the Rustler, however, will prevent any significant changes in groundwater density from occurring within the Culebra over the timescales for which increased precipitation and recharge are anticipated.  No other natural events or processes have been identified that could result in freshwater intrusion into units above the Salado or cause a significant decrease in fluid density.  Freshwater intrusion has therefore been eliminated from PA calculations on the basis of low probability of occurrence over the next 10,000 years.

Hydrological Response to Earthquakes has been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.

No new information has been identified for this FEP since the CRA-2004.

There are a variety of hydrological responses to earthquakes Some of these responses, such as changes in surface-water flow directions, result directly from fault movement.  Others, such as changes in subsurface water chemistry and temperature, probably result from changes in flow pathways along the fault or fault zone.  According to Bredehoeft et al. (1987, p. 139), further away from the region of fault movement, two types of changes to groundwater levels may take place as a result of changes in fluid pressure.

·       The passage of seismic waves through a rock mass causes a volume change, inducing a transient response in the fluid pressure, which may be observed as a short-lived fluctuation of the water level in wells.

·       Changes in volume strain can cause long-term changes in water level.  A buildup of strain occurs prior to rupture and is released during an earthquake.  The consequent change in fluid pressure may be manifested by the drying up or reactivation of springs some distance from the region of the epicenter.

Fluid-pressure changes induced by the transmission of seismic waves can produce changes of up to several meters (several yards) in groundwater levels in wells, even at distances of thousands of kilometers from the epicenter.  These changes are temporary, however, and levels typically return to pre-earthquake levels in a few hours or days.  Changes in fluid pressure arising from changes in volume strain persist for much longer periods, but they are only potentially consequential in tectonic regimes where there is a significant buildup of strain.  The regional tectonics of the Delaware Basin indicates that such a buildup has a low probability of occurring over the next 10,000 years (see FEPs N3 and N4, Section SCR-4.1.2.1).

The expected level of seismic activity in the region of the WIPP will be of low consequence to the performance of the disposal system in terms of groundwater flow or contaminant transport.  Changes in groundwater levels resulting from more distant earthquakes will be too short in duration to be significant.  Thus hydrological response to earthquakes has been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.

Changes in groundwater flow arising from Natural Gas Intrusion have been eliminated from PA calculations on the basis of low probability of occurrence over 10,000 years.

No new information has been identified for this FEP since the CRA-2004.

Hydrocarbon resources are present in formations beneath the WIPP (the CCA, Chapter 2.0, Section 2.3.1.2), and natural gas is extracted from the Morrow Formation.  These reserves are, however, some 4,200 m (14,000 ft) below the surface, and no natural events or processes have been identified that could result in natural gas intrusion into the Salado or the units above.  Natural gas intrusion has therefore been eliminated from PA calculations on the basis of low probability of occurrence over the next 10,000 years.

Groundwater Geochemistry in the hydrological units of the disposal system is accounted for in PA calculations.

No new information for this FEP has been identified since the CRA-2004.

The most important aspect of groundwater geochemistry in the region of the WIPP in terms of chemical retardation and colloid stability is salinity.  Groundwater geochemistry is discussed in detail in the CCA, Chapter 2.0, Section 2.2 and Section 2.4 and summarized here. The Delaware Mountain Group, Castile, and Salado contain basinal brines.  Waters in the Castile and Salado are at or near halite saturation.  Above the Salado, groundwaters are also relatively saline, and groundwater quality is poor in all of the permeable units.  Waters from the Culebra vary spatially in salinity and chemistry.  They range from saline sodium chloride-rich waters to brackish calcium sulfate-rich waters.  In addition, a range of magnesium-to-calcium ratios has been observed, and some waters reflect the influence of potash mining activities, having elevated potassium-to-sodium ratios.  Waters from the Santa Rosa are generally of better quality than those from the Rustler.  Salado and Castile brine geochemistry is accounted for in PA calculations of the actinide (An) source term (the CCA, Chapter 6.0, Section 6.4.3.4).  Culebra brine geochemistry is accounted for in the retardation factors used in PA calculations of actinide transport (see the CCA, Chapter 6.0, Section 6.4.6.2).

The effects of Saline Intrusion and Dissolution on groundwater chemistry have been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.

No new information has been identified for these FEPs since the CRA-2004.

Saline intrusion and effects of dissolution are considered together in this discussion because dissolution of minerals such as halite (NaCl), anhydrite (CaSO4), or gypsum (CaSO4×2H2O) (N38) could – in the most extreme case – increase the salinity of groundwaters in the Culebra to levels characteristic of those expected after saline intrusion (N34).

No natural events or processes have been identified that could result in saline intrusion into units above the Salado.  Injection of Castile or Salado brines into the Culebra as a result of human intrusion, an anthropogenically induced event, was included in past PA calculations.  Laboratory studies carried out to evaluate radionuclide transport in the Culebra following human intrusion produced data that can also be used to evaluate the consequences of natural saline intrusion.

The possibility that dissolution of halite, anhydrite, or gypsum might result in an increase in the salinity of low- to moderate-ionic-strength groundwaters in the Culebra also appears unlikely, despite the presence of halite in the Los Medaños under most of the WIPP site (Siegel and Lambert 1991, Figure 1-13), including the expected Culebra off-site transport pathway (the direction of flow from the point(s) at which brines from the repository would enter the Culebra, flow towards the south or south-southeast, and eventually to the boundary of the WIPP site).  (The Los Medaños Member of the Rustler, formerly referred to as the unnamed lower member of the Rustler, underlies the Culebra.)  A dissolution-induced increase in the salinity of Culebra groundwaters is unlikely because (1) the dissolution of halite is known to be rapid; (2) (moderate-ionic-strength) groundwaters along the off-site transport pathway (and at many other locations in the Culebra) have had sufficient time to dissolve significant quantities of halite, if this mineral is present in the subjacent Los Medaños and if Culebra fluids have been in contact with it; and (3) the lack of high-ionic-strength groundwaters along the off-site transport pathway (and elsewhere in the Culebra) implies that halite is present in the Los Medaños but Culebra fluids have not contacted it, or that halite is not present in the Los Medaños.  Because halite dissolves so rapidly if contacted by undersaturated solutions, this conclusion does not depend on the nature and timing of Culebra recharge (i.e., whether the Rustler has been a closed hydrologic system for several thousand to a few tens of thousands of years, or is subject to significant modern recharge).

Nevertheless, saline intrusion would not affect the predicted transport of thorium (Th), uranium (U), plutonium (Pu), and americium (Am) in the Culebra.  This is because (1) the laboratory studies that quantified the retardation of Th, U, Pu, and Am for the CCA PA were carried out with both moderate-ionic-strength solutions representative of Culebra groundwaters along the expected off-site transport pathway and high-ionic-strength solutions representative of brines from the Castile and the Salado (Brush 1996; Brush and Storz 1996); and (2) the results obtained with the Castile and Salado brines were – for the most part – used to predict the transport of Pu(III) and Am(III); Th(IV), U(IV), Np(IV), and Pu(IV); and U(VI).  The results obtained with the saline solutions were used for these actinide oxidation states because the extent to which saline and Culebra brines will mix along the offsite transport pathway in the Culebra was unclear at the time of the CCA PA; therefore, Brush (1996) and Brush and Storz (1996) recommended that PA use the results that predict less retardation.  In the case of Pu(III) and Am(III); Th(IV), U(IV), Np(IV), and Pu(IV); and U(VI), the retardation distribution coefficient (Kds) obtained with the saline solutions were somewhat lower than those obtained with the Culebra fluids.  The Kds recommended by Brush and Storz (1996) are being used for the CRA-2009 PA.  These Kds are also based mainly on results obtained with saline solutions.

Finally, it is important to reiterate that the use of results from laboratory studies with saline solutions to predict radionuclide transport in the Culebra for previous PAs and the CRA-2009 PA implement the effects of saline intrusion caused by human intrusion, not natural saline intrusion.  The conclusions that natural saline intrusion is unlikely, that significant dissolution is unlikely, and that these events or processes would have no significant consequence – in the unlikely event that they occur – continue to be valid.

The effects of Freshwater Intrusion on groundwater chemistry have been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.  Changes in Groundwater Eh and Changes in Groundwater pH have been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.

No new information has been identified for this FEP since the CRA-2004.

Natural changes in the groundwater chemistry of the Culebra and other units that resulted from saline intrusion or freshwater intrusioncould potentially affect chemical retardation and the stability of colloids.  Changes in groundwater Eh and groundwater pH could also affect the migration of radionuclides (see FEPs W65 to W70, Section SCR-6.5.5.2, Section SCR-6.5.5.3, Section SCR-6.5.6.1, and Section SCR-6.5.6.2).  No natural EPs have been identified that could result in saline intrusion into units above the Salado, and the magnitude of any natural temporal variation from the effects of dissolution on groundwater chemistry, or because of changes in recharge, is likely to be no greater than the present spatial variation.  These FEPs related to the effects of future natural changes in groundwater chemistry have been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.

The most likely mechanism for (natural) freshwater intrusion into the Culebra (N35), changes in groundwater Eh (N36), and changes in groundwater pH (N37) is (natural) recharge of the Culebra.  (Other FEPs consider possible anthropogenically induced recharge).  These three FEPs are closely related because an increase in the rate of recharge could reduce the ionic strength(s) of Culebra groundwaters, possibly enough to saturate the Culebra with (essentially) fresh water, at least temporarily.  Such a change in ionic strength could, if enough atmospheric oxygen remained in solution, also increase the Eh of Culebra groundwaters enough to oxidize Pu from the relatively immobile III and IV oxidation states (Pu(III) and Pu(IV)) – the oxidation states expected under current conditions (Brush 1996; Brush and Storz 1996) – to the relatively mobile V and VI oxidation states (Pu(V) and Pu(VI)).  Similarly, recharge of the Culebra with freshwater could also change the pH of Culebra groundwaters from the currently observed range of about 6 to 7 to mildly acidic values, thus (possibly) decreasing the retardation of dissolved Pu and Am.  (These changes in ionic strength, Eh, and pH could also affect mobilities of Th, U, and neptunium (Np), but the long-term performance of the WIPP is much less sensitive to the mobilities of these radioelements than to those of Pu and Am.)

There is still considerable uncertainty regarding the extent and timing of recharge to the Culebra.  Lambert (1986), Lambert and Carter (1987), and Lambert and Harvey (1987) used a variety of stable and radiogenic isotopic-dating techniques to conclude that the Rustler (and the Dewey Lake) have been closed hydrologic systems for several thousand to a few tens of thousands of years.  In other words, the last significant recharge of the Rustler occurred during the late Pleistocene in response to higher levels of precipitation and infiltration associated with the most recent continental glaciation of North America, and the current flow field in the Culebra is the result of the slow discharge of groundwater from this unit.  Other investigators have agreed that it is possible that Pleistocene recharge has contributed to present-day flow patterns in the Culebra, but that current patterns are also consistent with significant current recharge (Haug et al. 1987; Davies 1989).  Still others (Chapman 1986, 1988) have rejected Lambert’s interpretations in favor of exclusively modern recharge, at least in some areas.  For example, the low salinity of Hydrochemical Zone B south of the WIPP site could represent dilution of Culebra groundwater with significant quantities of recently introduced meteoric water (see Siegel et al. 1991, pp. 2-57–2-62 and Figure 2-17 for definitions and locations of the four hydrochemical facies in the Culebra in and around the WIPP site).

The current program to explain the cause(s) of the rising water levels observed in Culebra monitoring wells may elucidate the nature and timing of recharge.  However, the justification of this screening decision does not depend on how this issue is resolved.  If recharge occurs mainly during periods of high precipitation (pluvials) associated with periods of continental glaciation, the consequences of such recharge are probably already reflected in the ranges of geochemical conditions currently observed in the Culebra as a whole, as well as along the likely offsite transport pathway (the direction of flow from the point(s) at which brines from the repository would enter the Culebra in the event of human intrusion to the south or south-southeast and eventually to the boundary of the WIPP site).  Hence, the effects of recharge, (possible) freshwater intrusion, and (possible) concomitant changes in groundwater Eh and pH can be screened out on the basis of low consequence to the performance of the far-field barrier.  The reasons for the conclusion that the effects of pluvial recharge are inconsequential (i.e., are already included among existing variations in geochemical conditions) are (1) as many as 50 continental glaciations and associated pluvials have occurred since the late Pliocene Epoch 2.5 million years ago (2.5 Ma BP); (2) the glaciations and pluvials that have occurred since about 0.5 to 1 Ma BP have been significantly more severe than those that occurred prior to 1 Ma BP (see, for example, Servant 2001); (3) the studies that quantified the retardation of Th, U, Pu, and Am for the CCA PA calculations and the CCA Performance Assessment Verification Test (PAVT) were carried out under conditions that encompass those observed along the likely Culebra off-site transport pathway (Brush 1996; Brush and Storz 1996); and (4) these studies demonstrated that conditions in the Culebra are favorable for retardation of actinides despite the effects of as many as 50 periods of recharge.

It is also worth noting that the choice of the most recent glacial maximum as an upper limit for possible climatic changes during the 10,000-year (yr) WIPP regulatory period (Swift 1991; the CCA, Appendix CLI) established conservative upper limits for precipitation and recharge of the Culebra at the WIPP site.  The review by Swift (1991), later incorporated in the CCA, Appendix CLI, provides evidence that precipitation in New Mexico did not attain its maximum level (about 60-100% of current precipitation) until a few thousand years before the last glacial maximum.  Swift (1991) pointed out,

Prior to the last glacial maximum 22 to 18 ka BP, evidence from mid- Wisconsin faunal assemblages in caves in southern New Mexico, including the presence of extralimital species such as the desert tortoise that are now restricted to warmer climates, suggests warm summers and mild, relatively dry winters (Harris 1987, 1988).  Lacustrine evidence confirms the interpretation that conditions prior to and during the glacial advance that were generally drier than those at the glacial maximum.  Permanent water did not appear in what was later to be a major lake in the Estancia Valley in central New Mexico until sometime before 24 ka BP (Bachhuber 1989).  Late-Pleistocene lake levels in the San Agustin Plains in western New Mexico remained low until approximately 26.4 ka BP, and the d18O record from ostracode shells suggests that mean annual temperatures at that location did not decrease significantly until approximately 22 ka BP (Phillips et al. 1992).

Therefore, it is likely that precipitation and recharge did not attain levels characteristic of the most recent glacial maximum until about 70,000 to 75,000 years after the last glaciations had begun.  High-resolution, deep-sea d18O data (and other data) reviewed by Servant (2001, Figure 1 and Figure 2) support the conclusion that, although the volume of ice incorporated in continental ice sheets can expand rapidly at the start of a glaciation, attainment of maximum volume does not occur until a few thousand or a few tens of thousands of years prior to the termination of the approximately 100,000-yr glaciations that have occurred during the last 0.5 to 1 Ma BP.  Therefore, it is unlikely that precipitation and recharge will reach their maximum levels during the 10,000-yr regulatory period.

If, on the other hand, significant recharge occurs throughout both phases of the glacial-interglacial cycles, the conclusion that the effects of pluvial and modern recharge are inconsequential (i.e., are already reflected by existing variations in geochemical conditions) is also still valid.  The effects of future natural changes in groundwater chemistry have been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.

Relevant aspects of the Physiography, geomorphology, and topography of the region around the WIPP are accounted for in PA calculations.

No new information has been identified for this FEP since the CRA-2004.

Physiography and geomorphology are discussed in detail in the CCA, Chapter 2.0, Section 2.1.4, and are accounted for in the setup of the PA calculations (the CCA, Chapter 6.0, Section 6.4.2).

Disruption arising from the Impact of a Large Meteorite has been eliminated from PA calculations on the basis of low probability of occurrence over 10,000 years.

This FEP has been modified to correct errors discovered in Equations (SCR.5) and (SCR.6).  As a result of these error corrections, it is necessary to select an upper bound on the distribution of meteorite sizes; Ceres, the largest known asteroid, has been used to determine the upper bound.

Meteors frequently enter the earth’s atmosphere, but most of these are small and burn up before reaching the ground.  Of those that reach the ground, most produce only small impact craters that would have no effect on the postclosure integrity of a repository 650 m (2,150 ft) below the ground surface.  While the depth of a crater may be only one-eighth of its diameter, the depth of the disrupted and brecciated material is typically one-third of the overall crater diameter (Grieve 1987, p. 248).  Direct disruption of waste at the WIPP would only occur with a crater larger than 1.8 km (1.1 mi) in diameter.  Even if waste were not directly disrupted, the impact of a large meteorite could create a zone of fractured rocks beneath and around the crater.  The extent of such a zone would depend on the rock type.  For sedimentary rocks, the zone may extend to a depth of half the crater diameter or more (Dence et al. 1977, p. 263).  The impact of a meteorite causing a crater larger than 1 km (0.6 mi) in diameter could thus fracture the Salado above the repository.

Geological evidence for meteorite impacts on earth is rare because many meteorites fall into the oceans and erosion and sedimentation serve to obscure craters that form on land. Dietz (1961) estimated that meteorites that cause craters larger than 1 km (0.6 mi) in diameter strike the earth at the rate of about one every 10,000 years (equivalent to about 2 ´ 10-13 impacts per square kilometer per year).  Using observations from the Canadian Shield, Hartmann (1965, p. 161) estimated a frequency of between 0.8 ´ 10-13 and 17 ´ 10-13 impacts/km2/yr for impacts causing craters larger than 1 km (0.6 mi).  Frequencies estimated for larger impacts in studies reported by Grieve (1987, p. 263) can be extrapolated to give a rate of about 1.3 ´ 10-12 impacts/km2/yr for craters larger than 1 km (0.6 mi).  It is commonly assumed that meteorite impacts are randomly distributed across the earth’s surface, although Halliday (1964, pp. 267-277) calculated that the rate of impact in polar regions would be some 50 to 60 percent of that in equatorial regions.  The frequencies reported by Grieve (1987) would correspond to an overall rate of about 1 per 1,000 years on the basis of a random distribution.

Assuming the higher estimated impact rate of 17 ´ 10-13 impacts per square kilometer per year for impacts leading to fracturing of sufficient extent to affect a deep repository, and assuming a repository footprint of 1.4 km ´1.6 km (0.9 mi ´ 1.0 mi) for the WIPP, yields a frequency of about 4 ´ 10-12 impacts per year for a direct hit above the repository.  This impact frequency is several orders of magnitude below the screening threshold of 10-4 per 10,000 years provided in 40 CFR § 194.32(d).

Meteorite hits directly above the repository footprint are not the only impacts of concern, however, because large craters may disrupt the waste panels even if the center of the crater is outside the repository area.  It is possible to calculate the frequency of meteorite impacts that could disrupt a deep repository such as the WIPP by using the conservative model of a cylinder of rock fractured to a depth equal to one-half the crater diameter, as shown in the CCA, Appendix SCR, Figure SCR-1.  The area within which a meteorite could impact the repository is calculated by

                                                                                    (SCR.1)

where

L     =    length of the repository footprint (km)

W    =    width of the repository footprint (km)

D     =    diameter of the impact crater (km)

SD    =    area of the region where the crater would disrupt the repository (km2)

There are insufficient data on meteorites that have struck the earth to derive a distribution function for the size of craters directly.  Using meteorite impacts on the moon as an analogy, however, Grieve (1987, p. 257) derived the following distribution function:

                                                                                                                      (SCR.2)

where

FD   =    frequency of impacts resulting in craters larger than D (impacts/km2/yr).

If f(D) denotes the frequency of impacts giving craters of diameter D, then the frequency of impacts giving craters larger than D is

                                                                                                            (SCR.3)

and

                                                                                                  (SCR.4)

where

F1    =    frequency of impacts resulting in craters larger than 1 km (impacts/km2/yr)

f(D) =    frequency of impacts resulting in craters of diameter D ((impacts/km2/yr)

The overall frequency of meteorite impacts, in the size range of interest, that could disrupt or fracture the repository is thus given by

                                                                                                    (SCR.5)

where

h      =    depth to repository (kilometers),

M    =    maximum size of meteorite considered (kilometers)

N     =    frequency of impacts leading to disruption of the repository (impacts per year), and

                                                                                    (SCR.6)

Conservatively using the size (933 km [550 mi]) of the largest known asteroid, Ceres (Tedesco 1992), for the maximum size considered and if it is assumed that the repository is located at a depth of 650 m (2,150 ft) and has a footprint area of 1.4 km ´1.6 km (0.9 mi ´ 1.0 mi) and that meteorites creating craters larger than 1 km in diameter hit the earth at a frequency (F1) of 17 ´ 10-13 impacts/km2/yr, then Equation (SCR.6)gives a frequency of approximately 5.6 ´ 10-11 impacts per year for impacts disrupting the repository.  If impacts are randomly distributed over time, this corresponds to a probability of 5.6 ´ 10-7 over 10,000 years.

Similar calculations have been performed that indicate rates of impact of between 10-12 and 10-13 per year for meteorites large enough to disrupt a deep repository (see, for example, Hartmann 1979, Kärnbränslesakerhet 1978, Claiborne and Gera 1974, Cranwell et al. 1990, and Thorne 1992).  Meteorite impact can thus be eliminated from PA calculations on the basis of low probability of occurrence over 10,000 years.

Assuming a random or nearly random distribution of meteorite impacts, cratering at any location is inevitable given sufficient time.  Although repository depth and host-rock lithology may reduce the consequences of a meteorite impact, there are no repository locations or engineered systems that can reduce the probability of impact over 10,000 years.

The effects of Chemical Weathering and Mechanical Weathering have been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.

No new information has been identified for these FEPs since the CRA-2004.

Mechanical weathering and chemical weathering are assumed to be occurring at or near the surface around the WIPP site through processes such as exfoliation and leaching. The extent of these processes is limited and they will contribute little to the overall rate of erosion in the area or to the availability of material for other erosional processes. The effects of chemical weathering and mechanical weathering have been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.

The effects of Fluvial Erosion, Aeolian Erosion, and Mass Wasting in the region of the WIPP have been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.

No new information has been identified for these FEPs since the CRA-2004.

The geomorphological regime on the Mescalero Plain (Los Medaños) in the region of the WIPP is dominated by aeolian processes.  Dunes are present in the area, and although some are stabilized by vegetation, aeolian erosion will occur as they migrate across the area.  Old dunes will be replaced by new dunes, and no significant changes in the overall thickness of aeolian material are likely to occur.

Currently, precipitation in the region of the WIPP is too low (about 33 centimeters [cm] [13 inches (in.)] per year) to cause perennial streams, and the relief in the area is too low for extensive sheet flood erosion during storms.  An increase in precipitation to around 61 cm (24 in.) per year in cooler climatic conditions could result in perennial streams, but the nature of the relief and the presence of dissolution hollows and sinks will ensure that these streams remain small.  Significant fluvial erosion is not expected during the next 10,000 years.

Mass wasting (the downslope movement of material caused by the direct effect of gravity) is important only in terms of sediment erosion in regions of steep slopes.  In the vicinity of the WIPP, mass wasting will be insignificant under the climatic conditions expected over the next 10,000 years.

Erosion from wind, water, and mass wasting will continue in the WIPP region throughout the next 10,000 years at rates similar to those occurring at present.  These rates are too low to affect the performance of the disposal system significantly.  Thus the effects of fluvial erosion, aeolian erosion, and mass wasting have been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.

Soil Development has been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.

No new information has been identified for this FEP since the CRA-2004.

The Mescalero caliche is a well-developed calcareous remnant of an extensive soil profile across the WIPP site and adjacent areas. Although this unit may be up to 3 m (10 ft) thick, it is not continuous and does not prevent infiltration to the underlying formations. At Nash Draw, this caliche, dated in Lappin et al. (1989, pp. 2-4) at 410,000 to 510,000 years old, is present in collapse blocks, indicating some growth of Nash Draw in the late Pleistocene.  Localized gypsite spring deposits about 25,000 years old occur along the eastern flank of Nash Draw, but the springs are not currently active. The Berino soil, interpreted as 333,000 years old (Rosholt and McKinney 1980, Table 5), is a thin soil horizon above the Mescalero caliche. The persistence of these soils on the Livingston Ridge and the lack of deformation indicates the relative stability of the WIPP region over the past half-million years.

Continued growth of caliche may occur in the future but will be of low consequence in terms of its effect on infiltration. Other soils in the area are not extensive enough to affect the amount of infiltration that reaches underlying aquifers. Soil development has been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.

The effects of Aeolian Deposition, Fluvial Deposition, and Lacustrine Deposition and sedimentation in the region of the WIPP have been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.

No new information has been identified for these FEPs since the CRA-2004.

The geomorphological regime on the Mescalero Plain (Los Medaños) in the region of the WIPP is dominated by aeolian processes, but although some dunes are stabilized by vegetation, no significant changes in the overall thickness of aeolian material are expected to occur.  Vegetational changes during periods of wetter climate may further stabilize the dune fields, but aeolian deposition is not expected to significantly increase the overall thickness of the superficial deposits.

The limited extent of water courses in the region of the WIPP, under both present-day conditions and under the expected climatic conditions, will restrict the amount of fluvial deposition and lacustrine deposition in the region.

Mass wasting (deposition) may be significant if it results in dams or modifies streams.  In the region around the WIPP, the Pecos River forms a significant water course some 19 km (12 mi) away, but the broadness of its valley precludes either significant mass wasting or the formation of large impoundments.

Sedimentation from wind, water, and mass wasting is expected to continue in the WIPP region throughout the next 10,000 years at the low rates similar to those occurring at present.  These rates are too low to significantly affect the performance of the disposal system.  Thus the effects of aeolian deposition, fluvial deposition, and lacustrine deposition and sedimentation resulting from mass wasting have been eliminated from PA calculations on the basis of low consequence.

Stream and River Flow has been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.

No new information has been identified for this FEP since the CRA-2004.

No perennial streams are present at the WIPP site, and there is no evidence in the literature indicating that such features existed at this location since the Pleistocene (see, for example, Powers et al. 1978; and Bachman 1974, 1981, and 1987b).  The Pecos River is approximately 19 km (12 mi) from the WIPP site and more than 90 m (300 ft) lower in elevation.  Stream and river flow has been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.

The effects of Surface Water Bodies have been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.

No new information has been identified for this FEP since the CRA-2004.

No standing surface water bodies are present at the WIPP site, and there is no evidence in the literature indicating that such features existed at this location during or after the Pleistocene (see, for example, Powers et al. 1978; and Bachman 1974, 1981, and 1987b).  In Nash Draw, lakes and spoil ponds associated with potash mines are located at elevations 30 m (100 ft) below the elevation of the land surface at the location of the waste panels.  There is no evidence in the literature to suggest that Nash Draw was formed by stream erosion or was at any time the location of a deep body of standing water, although shallow playa lakes have existed there at various times.  Based on these factors, the formation of large lakes is unlikely and the formation of smaller lakes and ponds is of little consequence to the performance of the disposal system.  The effects of surface water bodies have therefore been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.

Groundwater Recharge, Groundwater Discharge, and Infiltration are accounted for in PA calculations.

No new information has been identified for these FEPs since the CRA-2004.

The groundwater basin described in the CCA, Chapter 2.0, Section 2.2.1.4 is governed by flow from areas where the water table is high to areas where the water table is low.  The height of the water table is governed by the amount of groundwater recharge reaching the water table, which in turn is a function of the vertical hydraulic conductivity and the partitioning of precipitation between evapotranspiration, runoff, and Infiltration.  Flow within the Rustler is also governed by the amount of groundwater discharge that takes place from the basin.  In the region around the WIPP, the principal discharge areas are along Nash Draw and the Pecos River.  Groundwater flow modeling accounts for infiltration, recharge, and discharge (the CCA, Chapter 2.0, Section 2.2.1.4 and Chapter 6.0, Section 6.4.10.2).

Changes in Groundwater Recharge and Discharge arising as a result of climate change are accounted for in PA calculations.

No new information has become available that would change the screening decision for this FEP.

Changes in recharge may affect groundwater flow and radionuclide transport in units such as the Culebra and Magenta dolomites.  Changes in the surface environment driven by natural climate change are expected to occur over the next 10,000 years (see FEPs N59 to N63).  Groundwater basin modeling (the CCA, Chapter 2.0, Section 2.2.1.4) indicates that a change in recharge will affect the height of the water table in the area of the WIPP, and that this will in turn affect the direction and rate of groundwater flow.

The present-day water table in the vicinity of the WIPP is within the Dewey Lake at about 980 m (3,215 ft) above mean sea level (the CCA, Chapter 2.0, Section 2.2.1.4.2.1).  An increase in recharge relative to present-day conditions would raise the water table, potentially as far as the local ground surface.  Similarly, a decrease in recharge could result in a lowering of the water table.  The low transmissivity of the Dewey Lake and the Rustler ensures that any such lowering of the water table will be at a slow rate, and lateral discharge from the groundwater basin is expected to persist for several thousand years after any decrease in recharge.  Under the anticipated changes in climate over the next 10,000 years, the water table will not fall below the base of the Dewey Lake, and dewatering of the Culebra is not expected to occur during this period (the CCA, Chapter 2.0, Section 2.2.1.4).

Changes in groundwater recharge and discharge is accounted for in PA calculations through definition of the boundary conditions for flow and transport in the Culebra (the CCA, Chapter 6.0, Section 6.4.9).

The effects of River Flooding and Lake Formation have been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.

No new information has been identified for this FEP since the CRA-2004.

Intermittent flooding of stream channels and the formation of shallow lakes will occur in the WIPP region over the next 10,000 years.  These may have a short-lived and local effect on the height of the water table, but are unlikely to affect groundwater flow in the Culebra.

Future occurrences of playa lakes or other longer-term floods will be remote from the WIPP and will have little consequence on system performance in terms of groundwater flow at the site.  There is no reason to believe that any impoundments or lakes could form over the WIPP site itself.  Thus river flooding and lake formation have been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.

Precipitation and Temperature are accounted for in PA calculations.

No new information has been identified for these FEPs since the CRA-2004.

The climate and meteorology of the region around the WIPP are described in the CCA, Section 2.5.2.  Precipitation in the region is low (about 33 cm [13 in.] per yr) and temperatures are moderate with a mean annual temperature of about 63 °F (17 °C).  Precipitation and temperature are important controls on the amount of recharge that reaches the groundwater system and are accounted for in PA calculations by use of a sampled parameter for scaling flow velocity in the Culebra (see Appendix PA-2009, Section PA-2.1.4.6).

Climate Change is accounted for in PA calculations.

No new information has been identified for this FEP since the CRA-2004.

Climate changes are instigated by changes in the earth’s orbit and by feedback mechanisms within the atmosphere and hydrosphere.  Models of these mechanisms, combined with interpretations of the geological record, suggest that the climate will become cooler and wetter in the WIPP region during the next 10,000 years as a result of natural causes.  Other changes, such as fluctuations in radiation intensity from the sun and variability within the many feedback mechanisms, will modify this climatic response to orbital changes.  The available evidence suggests that these changes will be less extreme than those arising from orbital fluctuations.

The effect of a change to cooler and wetter conditions is considered to be an increase in the amount of recharge, which in turn will affect the height of the water table (see FEPs N53 through N56, Section SCR-4.5.3.1 and SCR-4.5.3.2).  The height of the water table across the groundwater basin is an important control on the rate and direction of groundwater flow within the Culebra (see the CCA, Chapter 2.0, Section 2.2.1.4), and hence potentially on transport of radionuclides released to the Culebra through the shafts or intrusion boreholes.  Climate change is accounted for in PA calculations through a sampled parameter used to scale groundwater flow velocity in the Culebra (see Appendix PA-2009, Section PA-4.8).

Glaciation and the effects of Permafrost have been eliminated from PA calculations on the basis of low probability of occurrence over 10,000 years.

No new information has been identified for these FEPs since the CRA-2004.

No evidence exists to suggest that the northern part of the Delaware Basin has been covered by continental glaciers at any time since the beginning of the Paleozoic Era.  During the maximum extent of continental glaciation in the Pleistocene Epoch, glaciers extended into northeastern Kansas at their closest approach to southeastern New Mexico.  There is no evidence that alpine glaciers formed in the region of the WIPP during the Pleistocene glacial periods.

According to the theory that relates the periodicity of climate change to perturbations in the earth’s orbit, a return to a full glacial cycle within the next 10,000 years is highly unlikely (Imbrie and Imbrie 1980, p. 951).

Thus glaciation has been eliminated from PA calculations on the basis of low probability of occurrence over the next 10,000 years.  Similarly, a number of processes associated with the proximity of an ice sheet or valley glacier, such as permafrost and accelerated slope erosion (solifluction) have been eliminated from PA calculations on the basis of low probability of occurrence over the next 10,000 years.

The effects of Estuaries and Seas and Oceans have been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.

No new information has been identified for these FEPs since the CRA-2004.

The WIPP site is more than 800 km (480 mi) from the Pacific Ocean and from the Gulf of Mexico. Estuaries and seas and oceans have therefore been eliminated from PA calculations on the basis of low consequence to the disposal system.

Coastal Erosion and Marine Sediment Transport and Deposition have been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.

No new information has been identified for these FEPs since the CRA-2004.

The WIPP site is more than 800 km (480 mi) from the Pacific Ocean and Gulf of Mexico. The effects of coastal erosion and marine sediment transport and deposition have therefore been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.

The effects of both short-term and long-term Sea Level Changes have been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.

No new information has been identified for this FEP since the CRA-2004.

The WIPP site is some 1,036 m (3,400 ft) above sea level.  Global sea level changes may result in sea levels as much as 140 m (460 ft) below that of the present day during glacial periods, according to Chappell and Shackleton (1986, p. 138).  This can have marked effects on coastal aquifers.  During the next 10,000 years, the global sea level can be expected to drop towards this glacial minimum, but this will not affect the groundwater system in the vicinity of the WIPP.  Short-term changes in sea level, brought about by events such as meteorite impact, tsunamis, seiches, and hurricanes may raise water levels by several tens of meters. Such events have a maximum duration of a few days and will have no effect on the surface or groundwater systems at the WIPP site.  Anthropogenic-induced global warming has been conjectured by Warrick and Oerlemans (1990, p. 278) to result in longer-term sea level rise.  The magnitude of this rise, however, is not expected to be more than a few meters, and such a variation will have no effect on the groundwater system in the WIPP region.  Thus the effects of both short-term and long-term sea level changes have been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.

The effects of the natural Plants and Animals (flora and fauna) in the region of the WIPP have been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.

No new information has been identified for these FEPs since the CRA-2004.

The terrestrial and aquatic ecology of the region around the WIPP is described in the CCA, Chapter 2.0, Section 2.4.1.  The plants in the region are predominantly shrubs and grasses.  The most conspicuous animals in the area are jackrabbits and cottontail rabbits.  The effects of this flora and fauna in the region have been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.

The effects of Microbes on the region of the WIPP have been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.

No new information has been identified for this FEP since the CRA-2004.

Microbes are presumed to be present with the thin soil horizons.  Gillow et al. (2000) characterized the microbial distribution in Culebra groundwater at the WIPP site. Culebra groundwater contained 1.51 ± 1.08 ´ 105 cells/milliliter (mL). The dimension of the cells are 0.75 micrometer (mm) in length and 0.58 mm in width, right at the upper limit of colloidal particle size. Gillow et al. (2000) also found that at pH 5.0, Culebra denitrifier CDn (0.90 ± 0.02 ´ 108 cells/mL) removed 32% of the U added to sorption experiments, which is equivalent to 180 ± 10 milligrams U/g of dry cells. Another isolate from the WIPP (Halomonas sp.) (3.55 ± 0.11 ´ 108 cells/mL) sorbed 79% of the added U. Because of their large sizes, microbial cells as colloidal particles will be rapidly filtered out in the Culebra formation. Therefore, the original FEP screening decision that microbes in groundwater have an insignificant impact on radionuclide transport in the Culebra formation remains valid. A similar conclusion has also been arrived at for Swedish repository environments (Pedersen 1999).

The effects of Natural Ecological Development likely to occur in the region of the WIPP have been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.

No new information has been identified for this FEP since the CRA-2004.

The region around the WIPP is sparsely vegetated as a result of the climate and poor soil quality.  Wetter periods are expected during the regulatory period, but botanical records indicate that, even under these conditions, dense vegetation will not be present in the region (Swift 1992; see the CCA, Appendix CLI, p. 17).  The effects of the indigenous fauna are of low consequence to the performance of the disposal system and no natural events or processes have been identified that would lead to a change in this fauna that would be of consequence to system performance.  Natural ecological development in the region of the WIPP has therefore been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.


The following section presents screening arguments and decisions for human-induced EPs.  Table SCR-2 provides summary information regarding changes to human-induced EPs since the CCA.  Of the 58 human-induced EPs listed in the CRA-2004, 46 remain unchanged, 8 were updated with new information or were edited for clarity and completeness, 1 screening decision has been changed, and 3 EPs were split into 6 similar but more descriptive FEPs.  Thus, for the CRA-2009, there are now 61 human-induced EPs in the FEPs baseline.

The effects of historical, current, and near-future drilling associated with Oil and Gas Exploration, Potash Exploration, Oil and Gas Exploitation, Drilling for Other Resources, and Drilling for Enhanced Oil and Gas Recovery has been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system (see screening discussion for H21, H22, and H23).  Oil and gas exploration, potash exploration, oil and gas exploitation, drilling for other resources, and enhanced oil and gas recovery in the future is accounted for in DP scenarios through incorporation of the rate of future drilling as specified in section 194.33.

No new information has been identified for these FEPs since the CRA-2004.

Resource exploration and exploitation are the most common reasons for drilling in the Delaware Basin and are the most likely reasons for drilling in the near future.  The WIPP location has been evaluated for the occurrence of natural resources in economic quantities. Powers et al. (1978) (the CCA, Appendix GCR, Chapter 8) investigated the potential for exploitation of potash, hydrocarbons, caliche, gypsum, salt, uranium, sulfur, and lithium.  Also, in 1995, the New Mexico Bureau of Mines and Mineral Resources (NMBMMR) performed a reevaluation of the mineral resources at and within 1.6 km (1 mi) around the WIPP site (New Mexico Bureau of Mines and Mineral Resources 1995).  While some resources do exist at the WIPP site, for the HCN time frames, such drilling is assumed to only occur outside the WIPP site boundary.  This assumption is based on current federal ownership and management of the WIPP during operations, and assumed effectiveness of institutional controls for the 100-yr period immediately following site closure.

Drilling associated with oil and gas exploration and oil and gas exploitation currently takes place in the vicinity of the WIPP.  For example, gas is extracted from reservoirs in the Morrow Formation, some 4,200 m (14,000 ft) below the surface, and oil is extracted from shallower units within the Delaware Mountain Group, some 2,150 to 2,450 m (7,000 to 8,000 ft) below the surface.

Potash resources in the vicinity of the WIPP are discussed in the CCA, Chapter 2.0, Section 2.3.1.1.  Throughout the Carlsbad Potash District (CPD), commercial quantities of potash are restricted to the McNutt, which forms part of the Salado above the repository horizon.  Potash exploration and evaluation boreholes have been drilled within and outside the controlled area.  Such drilling will continue outside the WIPP land withdrawal boundary, but no longer occurs within the boundary because rights and controls have been transferred to the DOE.  Moreover, drilling for the evaluation of potash resources within the boundary will not occur throughout the time period of active institutional controls (AICs).

Drilling for other resources has taken place within the Delaware Basin.  For example, sulfur extraction using the Frasch process began in 1969 and continued for three decades at the Culberson County Rustler Springs mine near Orla, Texas.  In addition, brine wells have been in operation in and about the Delaware Basin for at least as long.  Solution mining processes for sulfur, salt (brine), potash, or any other mineral are not addressed in this FEP; only the drilling of the borehole is addressed here.  Resource extraction through solution mining and any potential effects are evaluated in Section SCR-5.2.2.3 (Solution Mining for Potash [H58]).  Nonetheless, the drilling activity associated with the production of other resources is not notably different than drilling for petroleum exploration and exploitation.

Drilling for the purposes of reservoir stimulation and subsequent enhanced oil and gas recovery does take place within the Delaware Basin, although systematic, planned waterflooding has not taken place near the WIPP.  Instead, injection near the WIPP consists of single-point injectors, rather than broad, grid-type waterflood projects (Hall et al. 2008).  In the vicinity of the WIPP, fluid injection usually takes place using boreholes initially drilled as producing wells.  Therefore, regardless of the initial intent of a deep borehole, whether in search of petroleum reserves or as an injection point, the drilling event and associated processes are virtually the same.  These drilling-related processes are addressed more fully in Section SCR-5.2.1.1 (Drilling Fluid Flow [H21]), Section SCR-5.2.1.2 (Drilling Fluid Loss [H22]), and Section SCR-5.2.1.3 (Blowouts [H23]) Discussion on the effects subsequent to drilling a borehole for the purpose of enhancing oil and gas recovery is discussed in Section SCR-5.2.1.6 (Enhanced Oil and Gas Production [H28]).

In summary, drilling associated with oil and gas exploration, potash exploration, oil and gas exploitation, enhanced oil and gas recovery, and drilling associated with Other Resources has taken place and is expected to continue in the Delaware Basin.  The potential effects of existing and possible near-future boreholes on fluid flow and radionuclide transport within the disposal system are discussed in FEPs H25 through H36 (Section SCR-5.2.1.5, Section SCR-5.2.1.6, Section SCR-5.2.1.7, Section SCR-5.2.1.8, Section SCR-5.2.1.9, Section SCR-5.2.1.10, Section SCR-5.2.1.11, Section SCR-5.2.1.12, and Section SCR-5.2.1.13), where low-consequence screening arguments are provided.

Criteria in section 194.33 require the DOE to examine the historical rate of drilling for resources in the Delaware Basin.  Thus consistent with 40 CFR § 194.33(b)(3)(i), the DOE has used the historical record of deep drilling associated with oil and gas exploration, potash exploration, oil and gas exploitation, enhanced oil and gas recovery, and drilling associated with other resources (sulfur exploration) in the Delaware Basin in calculations to determine the rate of future deep drilling in the Delaware Basin (see Section 33 of this application).

The effects of HCN and future drilling associated with Water Resources Exploration and Groundwater Exploitation have been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.  Historical shallow drilling associated with Water Resources Exploration and Groundwater Exploitation is accounted for in calculations to determine the rate of future shallow drilling.

The Delaware Basin Monitoring Program records and tracks the development of deep and shallow wells within the vicinity of the WIPP.  Updated drilling data is reported annually in the Delaware Basin Monitoring Annual Report (DOE 2007b).  While this information has been updated since the last recertification, it does not result in a change in the screening arguments or decisions of these FEPs.

Drilling associated with water resources exploration and groundwater exploitation has taken place and is expected to continue in the Delaware Basin. For the most part, water resources in the vicinity of the WIPP are scarce.  Elsewhere in the Delaware Basin, potable water occurs in places while some communities rely solely on groundwater sources for drinking water.  Even though water resources exploration and groundwater exploitation occur in the Basin, all such exploration/exploitation is confined to shallow drilling that extends no deeper than the Rustler.  Thus it will not impact repository performance because of the limited drilling anticipated in the future and the sizeable thickness of low-permeability Salado salt between the waste panels and the shallow groundwaters.  Given the limited groundwater resources and minimal consequence of shallow drilling on performance, the effects of HCN and future drilling associated with water resources exploration and groundwater exploitation have been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.  The screening argument therefore remains the same as given previously in the CCA.

Although shallow drilling for water resources exploration and groundwater exploitation have been eliminated from PA calculations, the Delaware Basin Drilling Surveillance Program (DBDSP) continues to collect drilling data related to water resources, as well as other shallow drilling activities.  As shown in the DBDSP 2007 Annual Report (U.S. Department of Energy 2007b), the total number of shallow water wells in the Delaware Basin is currently 2,296, compared to 2,331 shallow water wells reported in the CCA.  This decrease of 35 wells is attributed primarily to the reclassification of water wells to other types of shallow boreholes. Based on these data, the shallow drilling rate for water resources exploration and groundwater exploitation is essentially the same as reported in the CCA.  The distribution of groundwater wells in the Delaware Basin was included in the CCA, Appendix USDW, Section USDW.3.

Water is currently extracted from formations above the Salado, as discussed in the CCA, Chapter 2.0, Section 2.3.1.3.  The distribution of groundwater wells in the Delaware Basin is included in the CCA, Appendix USDW, Section USDW.3.  Water resources exploration and groundwaterexploitation are expected to continue in the Delaware Basin.

In summary, drilling associated with water resources exploration, groundwater exploitation, potash exploration, oil and gas exploration, oil and gas exploitation, enhanced oil and gas recovery, and drilling to explore other resources has taken place and is expected to continue in the Delaware Basin.  The potential effects of existing and possible near-future boreholes on fluid flow and radionuclide transport within the disposal system are discussed in Section SCR-5.2, where low-consequence screening arguments are provided.

Criteria in section 194.33 require that, to calculate the rates of future shallow and deep drilling in the Delaware Basin, the DOE should examine the historical rate of drilling for resources in the Delaware Basin.

Shallow drilling associated with water, potash, sulfur, oil, and gas extraction has taken place in the Delaware Basin over the past 100 years.  However, of these resources, only water and potash are present at shallow depths (less than 655 m (2,150 ft) below the surface) within the controlled area.  Thus, consistent with 40 CFR § 194.33(b)(4), the DOE includes drilling associated with water resources exploration, potash exploration, and groundwater exploitation in calculations to determine the rate of future shallow drilling in the Delaware Basin.  However, the effects of such events are not included in PA calculations because of low consequence to the performance of the disposal system.


Drilling associated with Archeological Investigations, Geothermal Energy Production, Liquid Waste Disposal, Hydrocarbon Storage, and Deliberate Drilling Intrusion have been eliminated from PA calculations on regulatory grounds.

No new information has been identified for these FEPs since the CRA-2004.

No drilling associated with archeology or geothermal energy production has taken place in the Delaware Basin.  Consistent with the future states assumptions in 40 CFR § 194.25(a) (U.S. Environmental Protection Agency 1996), such drilling activities have been eliminated from PA calculations on regulatory grounds.

While numerous archeological sites exist at and near the WIPP site, drilling for archeological purposes has not occurred.  Archeological investigations have only involved shallow surface disruptions, and do not require deeper investigation by any method, drilling or otherwise.  Geothermal energy is not considered to be a potentially exploitable resource because economically attractive geothermal conditions do not exist in the northern Delaware Basin.

Oil and gas production byproducts are disposed of underground in the WIPP region, but such liquid waste disposal does not involve drilling of additional boreholes (see H27, Section SCR-5.2.1.6); therefore drilling of boreholes for the explicit purpose of disposal has not occurred.

Hydrocarbon storage takes place in the Delaware Basin, but it involves gas injection through existing boreholes into depleted reservoirs (see, for example, Burton et al. 1993, pp. 66-67).  Therefore, drilling of boreholes for the explicit purpose of hydrocarbon storage has not occurred.

Consistent with section 194.33(b)(1), all near-future Human EPs relating to deliberate drilling intrusion into the WIPP excavation have been eliminated from PA calculations on regulatory grounds.

Consistent with section 194.33 and the future states assumptions in section 194.25(a), drilling for purposes other than resource recovery (such as WIPP site investigation) and drilling activities that have not taken place in the Delaware Basin over the past 100 years need not be considered in determining future drilling rates.  Thus drilling associated with archeological investigations, geothermal energy production, liquid waste disposal, hydrocarbon storage, and deliberate drilling intrusion have been eliminated from PA calculations on regulatory grounds.

As prescribed by section 194.32(b), the effects of HCN and future Conventional Underground Potash Mining are accounted for in PA calculations (see also FEP H37).

No new information has been identified for this FEP since the CRA-2004.

Potash is the only known economically viable resource in the vicinity of the WIPP that is recovered by underground mining (see the CCA, Chapter 2.0, Section 2.3.1).  Potash is mined extensively by conventional techniques in the region east of Carlsbad and up to 2.4 km (1.5 mi) from the boundaries of the controlled area of the WIPP.  According to existing plans and leases (see the CCA, Chapter 2.0, Section 2.3.1.1), potash mining is expected to continue in the vicinity of the WIPP in the near future.  The DOE assumes that all economically recoverable potash in the vicinity of the disposal system will be extracted in the near future, although there are no economical reserves above the WIPP waste panels (Griswold and Griswold 1999).

In summary, conventional underground potash mining is currently taking place and is expected to continue in the vicinity of the WIPP in the near future.  The potential effects of HCN and future conventional underground potash mining are accounted for in PA calculations as prescribed by section 194.32(b), and as further described in the supplementary information to Part 194 Subpart C, “Compliance Certification and Recertification” and in the Compliance Application Guidance (CAG), Subpart C, § 194.32, Scope of Performance Assessments.

HCN Mining for Other Resources has been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system. Future Mining for Other Resources has been eliminated from PA calculations on regulatory grounds.

Since the CCA, no changes in the resources sought via mining have occurred.

Potash is the only known economically viable resource in the vicinity of the WIPP that is recovered by underground mining.  Potash is mined extensively in the region east of Carlsbad and up to 5 km (3.1 mi) from the boundaries of the controlled area.  According to existing plans and leases, potash mining is expected to continue in the vicinity of the WIPP in the near future.  The DOE assumes that all economically recoverable potash in the vicinity of the disposal system will be extracted in the near future.  Excavation for resources other than potash and archaeological excavations have taken place or are currently taking place in the Delaware Basin.  These activities have not altered the geology of the controlled area significantly, and have been eliminated from PA calculations for the HCN timeframe on the basis of low consequence to the performance of the disposal system.

Potash is the only resource that has been identified within the controlled area in a quality similar to that currently mined elsewhere in the Delaware Basin.  Future mining for other resources has been eliminated from PA calculations on the regulatory basis of section 194.25(a).

Consistent with section 194.33(b)(1), near-future, human-induced EPs relating to Tunneling into the WIPP excavation and Construction of Underground Facilities have been eliminated from PA calculations on regulatory grounds.  Furthermore, consistent with section 194.25(a), future human-induced EPs relating to Tunneling into the WIPP excavation and Construction of Underground Facilities have been eliminated from PA calculations on regulatory grounds.

No new information has been identified for this FEP.

No tunneling or construction of underground facilities (for example, storage, disposal, accommodation [i.e., dwellings]) has taken place in the Delaware Basin.  Mining for potash occurs (a form of tunneling), but is addressed specifically in (Section SCR-5.1.2.1 (Conventional Underground Potash Mining [H13])).  Gas storage does take place in the Delaware Basin, but it involves injection through boreholes into depleted reservoirs, and not excavation (see, for example, Burton et al. 1993, pp. 66–67).

On April 26, 2001, the DOE formally requested approval for the installation of the OMNISita astrophysics experiment in the core storage alcove of the WIPP underground repository.  The purpose of the project is to develop a prototype neutrino detector to test proof-of-concept principles and measure background cosmic radiation levels within the WIPP underground repository.  EPA approved the request on August 29, 2001. This project does not require additional tunneling or excavation beyond the current repository footprint, and therefore does not impact the screening argument for this FEP.

Because tunneling and construction of underground facilities (other than WIPP) have not taken place in the Delaware Basin, and consistent with the future-states assumptions in section 194.25(a), such excavation activities have been eliminated from PA calculations on regulatory grounds.

HCN Archaeological Excavations have been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system. Future Archaeological Excavations into the disposal system have been eliminated from PA calculations on regulatory grounds.

No new information related to this FEP has been identified.

Archeological excavations have occurred at or near the WIPP, but involved only minor surface disturbances.  These archaeological excavations may continue into the foreseeable future as other archeological sites are discovered.  These activities have not altered the geology of the controlled area significantly, and have been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system for the HCN timeframe.

Also, consistent with section 194.32(a), which limits the scope of consideration of future human actions to mining and drilling, future archaeological excavations have been eliminated from PA calculations on regulatory grounds.

Consistent with section 194.33(b)(1), near-future, human-induced EPs relating to Deliberate Mining Intrusion into the WIPP excavation have been eliminated from PA calculations on regulatory grounds.  Furthermore, consistent with section 194.33(b)(1), future human-induced EPs relating to Deliberate Mining Intrusion into the WIPP excavation have been eliminated from PA calculations on regulatory grounds.

No new information has been identified for this FEP.

Consistent with section 194.33(b)(1), all future human-related EPs relating to deliberate mining intrusion into the WIPP excavation have been eliminated from PA calculations on regulatory grounds.

Historical underground Explosions for Resource Recovery have been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system. Future underground Explosions for Resource Recovery have been eliminated from PA calculations on regulatory grounds.

No new information has been identified for this FEP.

This section discusses subsurface explosions associated with resource recovery that may result in pathways for fluid flow between hydraulically conductive horizons.  The potential effects of explosions on the hydrological characteristics of the disposal system are discussed in Section SCR-5.2.3.1 (Changes in Groundwater Flow Due to Explosions [H39]).

Neither small-scale nor regional-scale explosive techniques to enhance the formation of hydraulic conductivity form a part of current mainstream oil- and gas-production technology.  Instead, controlled perforating and hydrofracturing are used to improve the performance of oil and gas boreholes in the Delaware Basin.  However, small-scale explosions have been used in the past to fracture oil- and natural-gas-bearing units to enhance resource recovery.  The size of explosion used to fracture an oil- or gas-bearing unit is limited by the need to contain the damage within the unit being exploited.  In the area surrounding the WIPP, the stratigraphic units with oil and gas resources are too deep for explosions to affect the performance of the disposal system.  Thus the effects of explosions for resource recovery have been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.

Potash mining is currently taking place and is expected to continue in the vicinity of the WIPP in the near future.  Potash is mined extensively in the region east of Carlsbad and up to 2.4 km (1.3 mi) from the boundaries of the controlled area. In earlier years conventional drill, blast, load, and rail-haulage methods were used. Today, continuous miners similar to those used in coal-mining have been adapted to fit the potash-salt formations. Hence, drilling and blasting technology is not used in the present day potash mines.  Thus the effects of explosions for resource recoveryhave been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.

Consistent with section 194.33(d), PAs need not analyze the effects of techniques used for resource recovery subsequent to the drilling of a future borehole.  Therefore, future underground explosions for resource recovery have been eliminated from PA calculations on regulatory grounds.

Historical Underground Nuclear Device Testing has been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.  Future Underground Nuclear Device Testing has been eliminated from PA calculations on regulatory grounds.

No new information has been identified related to this FEP.

The Delaware Basin has been used for an isolated nuclear test.  This test, Project Gnome (Rawson et al. 1965), took place in 1961 at a location approximately 13 km (8 mi) southwest of the WIPP waste disposal region.  Project Gnome was decommissioned in 1979.

The primary objective of Project Gnome was to study the effects of an underground nuclear explosion in salt.  The Gnome experiment involved the detonation of a 3.1 kiloton nuclear device at a depth of 360 m (1,190 ft) in the bedded salt of the Salado.  The explosion created an approximately spherical cavity of about 27,000 cubic meters (m3) (950,000 cubic feet [ft3]) and caused surface displacements in a radius of 360 m (1,180 ft).  No earth tremors perceptible to humans were reported at distances over 40 km (25 mi) from the explosion.  A zone of increased permeability was observed to extend at least 46 m (150 ft) laterally from and 105 m (344 ft) above the point of the explosion.  The test had no significant effects on the geological characteristics of the WIPP disposal system.  Thus historical underground nuclear device testing has been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.  There are no existing plans for underground nuclear device testing in the vicinity of the WIPP in the near future.

The criterion in section 194.32(a) relating to the scope of PAs limits the consideration of future human actions to mining and drilling.  Therefore, future underground nuclear device testing has been eliminated from PA calculations on regulatory grounds.

Drilling Fluid Flow associated with historical, current, near-future, and future boreholes that do not intersect the waste disposal region has been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.  The possibility of a future deep borehole penetrating a waste panel, such that drilling-induced flow results in transport of radionuclides to the land surface or to overlying hydraulically conductive units, is accounted for in PA calculations.  The possibility of a deep borehole penetrating both the waste disposal region and a Castile brine reservoir is accounted for in PA calculations.

The screening argument for this FEP has been revised slightly to remove confusion and inconsistency as suggested by the EPA in “TSD for Section 194.25, 194.32, and 194.33” (U.S. Environmental Protection Agency 2006).

Borehole circulation fluid could be lost to thief zones encountered during drilling, or fluid could flow from pressurized zones through the borehole to the land surface (blowout) or to a thief zone.  Such drilling-related EPs could influence groundwater flow and, potentially, radionuclide transport in the affected units.  Future drilling within the controlled area could result in direct releases of radionuclides to the land surface or transport of radionuclides between hydraulically conductive units.

Movement of brine from a pressurized zone through a borehole into potential thief zones such as the Salado interbeds or the Culebra could result in geochemical changes and altered radionuclide migration rates in these units.

Drilling fluid flow is a short-term event that can result in the flow of pressurized fluid from one geologic stratum to another.  However, long-term flow through abandoned boreholes would have a greater hydrological impact in the Culebra than a short-term event like drilling-induced flow outside the controlled area. Wallace (1996a) analyzed the potential effects of flow through abandoned boreholes in the future within the controlled area, and concluded that interconnections between the Culebra and deep units could be eliminated from PA calculations on the basis of low consequence.  Thus the HCN of drilling fluid flow associated with boreholes outside the controlled area has been screened out on the basis of low consequence to the performance of the disposal system.

As discussed in FEPs H25 through H36 (Section SCR-5.2.1.5, Section SCR-5.2.1.6, Section SCR-5.2.1.7, Section SCR-5.2.1.8, Section SCR-5.2.1.9, Section SCR-5.2.1.10, Section SCR-5.2.1.11, Section SCR-5.2.1.12, and Section SCR-5.2.1.13), drilling associated with water resources exploration, groundwater exploitation, potash exploration, oil and gas exploration, oil and gas exploitation, enhanced oil and gas recovery, and drilling to explore other resources has taken place or is currently taking place outside the controlled area in the Delaware Basin.  These drilling activities are expected to continue in the vicinity of the WIPP in the near future.

For the future, drill holes may intersect the waste disposal region and their effects could be more profound.  Thus the possibility of a future borehole penetrating a waste panel, so that drilling fluid flowand, potentially, blowout results in transport of radionuclides to the land surface or to overlying hydraulically conductive units, is accounted for in PA calculations.

The units intersected by the borehole may provide sources for fluid flow (brine, oil, or gas) to the waste panel during drilling.  In the vicinity of the WIPP, the Castile that underlies the Salado contains isolated volumes of brine at fluid pressures greater than hydrostatic.  A future borehole that penetrates a Castile brine reservoir could provide a connection for brine flow from the reservoir to the waste panel, thus increasing fluid pressure and brine volume in the waste panel.  The possibility of a deep borehole penetrating both a waste panel and a brine reservoir is accounted for in PA calculations.

Penetration of an underpressurized unit underlying the Salado could result in flow and radionuclide transport from the waste panel to the underlying unit during drilling, although drillers would minimize such fluid loss to a thief zone through the injection of materials to reduce permeability or through the use of casing and cementing.  Also, the permeabilities of formations underlying the Salado are less than the permeability of the Culebra (Wallace 1996a).  Thus the consequences associated with radionuclide transport to an underpressurized unit below the waste panels during drilling will be less significant, in terms of disposal system performance, than the consequences associated with radionuclide transport to the land surface or to the Culebra during drilling.  Through this comparison, drilling events that result in penetration of underpressurized units below the waste-disposal region have been eliminated from PA calculations on the basis of beneficial consequence to the performance of the disposal system.

Drilling Fluid Loss associated with HCN and future boreholes that do not intersect the waste disposal region has been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.  The possibility of a future Drilling Fluid Loss into waste panels is accounted for in PA calculations.

The screening argument for this FEP has been revised slightly to remove confusion and inconsistency as suggested by the EPA in “TSD for Section 194.25, 194.32, and 194.33” (U.S. Environmental Protection Agency 2006).

Drilling fluid loss is a short-term event that can result in the flow of pressurized fluid from one geologic stratum to another.  Large fluid losses would lead a driller to inject materials to reduce permeability, or it would lead to the borehole being cased and cemented to limit the loss of drilling fluid. Assuming such operations are successful, drilling fluid loss in the near future outside the controlled area will not significantly affect the hydrology of the disposal system. Thus drilling fluid loss associated with historical, current, and near-future boreholes has been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.

In evaluating the potential consequences of drilling fluid loss to a waste panel in the future, two types of drilling events need to be considered – those that intercept pressurized fluid in underlying formations such as the Castile (defined in the CCA, Chapter 6.0, Section 6.3.2.2 as E1 events), and those that do not (E2 events).  A possible hydrological effect would be to make a greater volume of brine available for gas generation processes and thereby increase gas volumes at particular times in the future.  For either type of drilling event, on the basis of current drilling practices, the driller is assumed to pass through the repository rapidly.  Relatively small amounts of drilling fluid loss might not be noticed and might not give rise to concern.  Larger fluid losses would lead to the driller injecting materials to reduce permeability, or to the borehole being cased and cemented, to limit the loss of drilling fluid.

For boreholes that intersect pressurized brine reservoirs, the volume of fluid available to flow up a borehole will be significantly greater than the volume of any drilling fluid that could be lost.  This greater volume of brine is accounted for in PA calculations, and is allowed to enter the disposal room (see the CCA, Chapter 6.0, Section 6.4.7).  Thus the effects of drilling fluid loss will be small by comparison to the potential flow of brine from pressurized brine reservoirs.  Therefore, the effects of drilling fluid loss for E1 drilling events have been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.

The consequences of drilling fluid loss into waste panels in the future are accounted for in PA calculations for E2 events.

Drilling fluid flow will not affect hydraulic conditions in the disposal system significantly unless there is substantial drilling fluid loss to a thief zone, such as the Culebra.  Typically, zones into which significant borehole circulation fluid is lost are isolated through injection of materials to reduce permeability or through casing and cementing programs.  Assuming such operations are successful, drilling fluid loss in the near future outside the controlled area will not affect the hydrology of the disposal system significantly and be of no consequence.

The consequences of drilling within the controlled area in the future will primarily depend on the location of the borehole.  Potentially, future deep drilling could penetrate the waste disposal region.  Hydraulic and geochemical conditions in the waste panel could be affected as a result of drilling fluid loss to the panel.

Penetration of an underpressurized unit underlying the Salado could result in flow and radionuclide transport from the waste panel to the underlying unit during drilling, although drillers would minimize such fluid loss to a thief zone through the injection of materials to reduce permeability or through the use of casing and cementing.  Also, the permeabilities of formations underlying the Salado are less than the permeability of the Culebra (Wallace 1996a).  Thus the consequences associated with radionuclide transport to an underpressurized unit below the waste panels during drilling will be less significant, in terms of disposal system performance, than the consequences associated with radionuclide transport to the land surface or to the Culebra during drilling.  Through this comparison, drilling events that result in penetration of underpressurized units below the waste-disposal region have been eliminated from PA calculations on the basis of beneficial consequence to the performance of the disposal system.

For boreholes that do not intersect pressurized brine reservoirs (but do penetrate the waste-disposal region), the treatment of the disposal room implicitly accounts for the potential for greater gas generation resulting from drilling fluid loss.  Thus the hydrological effects of drilling fluid loss for E2 drilling events are accounted for in PA calculations within the conceptual model of the disposal room for drilling intrusions.

Blowouts associated with HCN and future boreholes that do not intersect the waste disposal region have been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.  The possibility of a future deep borehole penetrating a waste panel such that drilling-induced flow results in transport of radionuclides to the land surface or to overlying hydraulically conductive units is accounted for in PA calculations.  The possibility of a deep borehole penetrating both the waste disposal region and a Castile brine reservoir is accounted for in PA calculations.

No new information is available for this FEP.

Blowouts are short-term events that can result in the flow of pressurized fluid from one geologic stratum to another.  For the near future, a blowout may occur in the vicinity of the WIPP but is not likely to affect the disposal system because of the distance from the well to the waste panels, assuming that AICs are in place which restrict borehole installation to outside the WIPP boundary.  Blowouts associated with HCN and future boreholes that do not intersect the waste disposal region have been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.  For the future, the drill holes may intersect the waste disposal region and these effects could be more profound.  Thus blowouts are included in the assessment of future activities and their consequences are accounted for in PA calculations.

Fluid could flow from pressurized zones through the borehole to the land surface (blowout) or to a thief zone.  Such drilling-related EPs could influence groundwater flow and, potentially, radionuclide transport in the affected units.  Movement of brine from a pressurized zone through a borehole into potential thief zones such as the Salado interbeds or the Culebra could result in geochemical changes and altered radionuclide migration rates in these units.

Drilling associated with water resources exploration, groundwater exploitation, potash exploration, oil and gas exploration, oil and gas exploitation, enhanced oil and gas recovery, and drilling to explore other resources has taken place or is currently taking place outside the controlled area in the Delaware Basin.  These drilling activities are expected to continue in the vicinity of the WIPP in the near future.

Naturally occurring brine and gas pockets have been encountered during drilling in the Delaware Basin.  Brine pockets have been intersected in the Castile (as discussed in the CCA, Chapter 2.0, Section 2.2.1.3) and in the Salado above the WIPP horizon (the CCA, Chapter 2.0, Section 2.2.1.2.2).  Gas blowouts have occurred during drilling in the Salado.  Usually, such events result in brief interruptions in drilling while the intersected fluid pocket is allowed to depressurize through flow to the surface (for a period lasting from a few hours to a few days).  Drilling then restarts with an increased drilling mud weight.  Under these conditions, blowouts in the near future will cause isolated hydraulic disturbances, but will not affect the hydrology of the disposal system significantly.

Potentially, the most significant disturbance to the disposal system could occur if an uncontrolled blowout during drilling resulted in substantial flow through the borehole from a pressurized zone to a thief zone.  For example, if a borehole penetrates a brine reservoir in the Castile, brine could flow through the borehole to the Culebra over the long term, and, as a result, could affect hydraulic conditions in the Culebra.  The potential effects of such an event can be compared to the effects of long-term fluid flow from deep overpressurized units to the Culebra through abandoned boreholes. Wallace (1996a) analyzed the potential effects of flow through abandoned boreholes in the future within the controlled area and concluded that interconnections between the Culebra and deep units could be eliminated from PA calculations on the basis of low consequence.  Long-term flow through abandoned boreholes would have a greater hydrological impact in the Culebra than short-term, drilling-induced flow outside the controlled area.  Thus the effects of fluid flow during drilling in the near future have been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.

In summary, blowouts associated with historical, current, and near-future boreholes have been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.

The consequences of drilling within the controlled area in the future will depend primarily on the location of the borehole.  Potentially, future deep drilling could penetrate the waste disposal region.  If the borehole intersects the waste in the disposal rooms, radionuclides could be transported as a result of drilling fluid flow: releases to the accessible environment may occur as material entrained in the circulating drilling fluid is brought to the surface.  Also, during drilling, contaminated brine may flow up the borehole and reach the surface, depending on fluid pressure within the waste disposal panels; blowout conditions could prevail if the waste panel were sufficiently pressurized at the time of intrusion.

The possibility of a future borehole penetrating a waste panel, so that drilling fluid flow and, potentially, blowout results in transport of radionuclides to the land surface or to overlying hydraulically conductive units, is accounted for in PA calculations.

The units intersected by the borehole may provide sources for fluid flow (brine, oil, or gas) to the waste panel during drilling.  In the vicinity of the WIPP, the Castile that underlies the Salado contains isolated volumes of brine at fluid pressures greater than hydrostatic.  A future borehole that penetrates a Castile brine reservoir could provide a connection for brine flow from the reservoir to the waste panel, thus increasing fluid pressure and brine volume in the waste panel.  The possibility of a deep borehole penetrating both a waste panel and a brine reservoir is accounted for in PA calculations.

Future boreholes could affect the hydraulic conditions in the disposal system.  Intersection of pockets of pressurized gas and brine would likely result in short-term, isolated hydraulic disturbances, and will not affect the hydrology of the disposal system significantly.  Potentially the most significant hydraulic disturbance to the disposal system could occur if an uncontrolled blowout during drilling resulted in substantial flow through the borehole from a pressurized zone to a thief zone.  For example, if a borehole penetrates a brine reservoir in the Castile, brine could flow through the borehole to the Culebra, and, as a result, could affect hydraulic conditions in the Culebra.  The potential effects of such an event can be compared to the effects of long-term fluid flow from deep overpressurized units to the Culebra through abandoned boreholes. Wallace (1996a) analyzed the potential effects of such interconnections in the future within the controlled area, concluding that flow through abandoned boreholes between the Culebra and deep units could be eliminated from PA calculations on the basis of low consequence.

Drilling-Induced Geochemical Changes that occur within the controlled area as a result of HCN and future drilling-induced flow are accounted for in PA calculations.

No new information is available for this FEP.

Borehole circulation fluid could be lost to thief zones encountered during drilling, or fluid could flow from pressurized zones through the borehole to the land surface (blowout) or to a thief zone.  Such drilling-related EPs could influence groundwater flow and, potentially, radionuclide transport in the affected units.  Future drilling within the controlled area could result in direct releases of radionuclides to the land surface or transport of radionuclides between hydraulically conductive units.

Movement of brine from a pressurized zone through a borehole and into potential thief zones such as the Salado interbeds or the Culebra, could result in geochemical changes and altered radionuclide migration rates in these units.

Drilling associated with resource exploration, exploitation, and recovery has taken place or is currently taking place outside the controlled area in the Delaware Basin.  These drilling activities are expected to continue in the vicinity of the WIPP in the near future.  Chemical changes induced by such drilling are discussed below.

Radionuclide migration rates are governed by the coupled effects of hydrological and geochemical processes (see discussions in FEPs W77 through W100, Section SCR-6.6.1.1, Section SCR-6.6.1.2, Section SCR-6.6.2.1, Section SCR-6.6.3.1, Section SCR-6.6.3.2, Section SCR-6.6.4.1, Section SCR-6.7.1.1, Section SCR-6.7.2.1, Section SCR-6.7.3.1, Section SCR-6.7.4.1, Section SCR-6.7.4.2, Section SCR-6.7.4.3, Section SCR-6.7.5.1, Section SCR-6.7.5.2, Section SCR-6.7.5.3, and Section SCR-6.7.5.4).  Human EPs outside the controlled area could affect the geochemistry of units within the controlled area if they occur sufficiently close to the edge of the controlled area.  Movement of brine from a pressurized reservoir in the Castile through a borehole into potential thief zones, such as the Salado interbeds or the Culebra, could cause drilling-induced geochemical changes resulting in altered radionuclide migration rates in these units through their effects on colloid transport and sorption (colloid transport may enhance radionuclide migration, while radionuclide migration may be retarded by sorption).

The treatment of colloids in PA calculations is described in the CCA, Chapter 6.0, Section 6.4.3.6 and Section 6.4.6.2.2.  The repository and its contents provide the main source of colloids in the disposal system.  By comparison, Castile brines have relatively low total colloid concentrations.  Therefore, changes in colloid transport in units within the controlled area as a result of HCN drilling-induced flow have been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.

Sorption within the Culebra is accounted for in PA calculations as discussed in the CCA, Chapter 6.0, Section 6.4.6.2.  The sorption model comprises an equilibrium, sorption isotherm approximation, employing Kds applicable to dolomite in the Culebra (the CRA-2004, Appendix PA, Attachment MASS, Section MASS-15.2).  The cumulative distribution functions (CDFs) of Kds used are derived from a suite of experimental studies that include measurements of Kds for actinides in a range of chemical systems including Castile brines, Culebra brines, and Salado brines.  Therefore, any changes in sorption geochemistry in the Culebra within the controlled area as a result of HCN drilling-induced flow are accounted for in PA calculations.

Sorption within the Dewey Lake is accounted for in PA calculations, as discussed in the CCA, Chapter 6.0, Section 6.4.6.6.  It is assumed that the sorptive capacity of the Dewey Lake is sufficiently large to prevent any radionuclides that enter the Dewey Lake from being released over 10,000 years (Wallace et al. 1995).  Sorption within other geological units of the disposal system has been eliminated from PA calculations on the basis of beneficial consequence to the performance of the disposal system.  The effects of changes in sorption in the Dewey Lake and other units within the controlled area as a result of HCN drilling-induced flow have been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.

The consequences of drilling within the controlled area in the future will primarily depend on the location of the borehole.  Future deep drilling could potentially penetrate the waste disposal region.  If the borehole intersects the waste in the disposal rooms, radionuclides could be transported as a result of drilling fluid flow and geochemical conditions in the waste panel could be affected as a result of drilling induced geochemical changes.

Drilling fluid loss to a waste panel could modify the chemistry of disposal room brines in a manner that would affect the solubility of radionuclides and the source term available for subsequent transport from the disposal room.  The majority of drilling fluids used are likely to be locally derived, and their bulk chemistry will be similar to fluids currently present in the disposal system.  In addition, the presence of the MgO chemical conditioner in the disposal rooms will buffer the chemistry across a range of fluid compositions, as discussed in detail in Appendix SOTERM-2009, Section SOTERM-2.3.2.  Furthermore, for E1 drilling events, the volume of Castile brine that flows into the disposal room will be greater than that of any drilling fluids; Castile brine chemistry is accounted for in PA calculations.  Thus the effects on radionuclide solubility of drilling fluid loss to the disposal room have been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.

Movement of brine from a pressurized reservoir in the Castile through a borehole into thief zones, such as the Salado interbeds or the Culebra, could result in geochemical changes in the receiving units, and thus alter radionuclide migration rates in these units through their effects on colloid transport and sorption.

The repository and its contents provide the main source of colloids in the disposal system.  Thus colloid transport in the Culebra within the controlled area as a result of drilling-induced flow associated with boreholes that intersect the waste disposal region is accounted for in PA calculations, as described in the CCA, Chapter 6.0, Section 6.4.3.6 and Section 6.4.6.2.1.  The Culebra is the most transmissive unit in the disposal system, and it is the most likely unit through which significant radionuclide transport could occur.  Therefore, colloid transport in units other than the Culebra, as a result of drilling fluid loss associated with boreholes that intersect the waste disposal region, has been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.

As discussed in FEPs H21, H22, and H23 (Section SCR-5.2.1.1, Section SCR-5.2.1.2, and Section SCR-5.2.1.3), sorption within the Culebra is accounted for in PA calculations.  The sorption model used incorporates the effects of changes in sorption in the Culebra as a result of drilling-induced flow associated with boreholes that intersect the waste disposal region.

Consistent with the screening discussion in FEPs H21, H22, and H23 (Section SCR-5.2.1.1, Section SCR-5.2.1.2, and Section SCR-5.2.1.3), the effects of changes in sorption in the Dewey Lake inside the controlled area as a result of drilling-induced flow associated with boreholes that intersect the waste disposal region have been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.  Sorption within other geological units of the disposal system has been eliminated from PA calculations on the basis of beneficial consequence to the performance of the disposal system.

Future boreholes that do not intersect the waste disposal region could nevertheless encounter contaminated material by intersecting a region into which radionuclides have migrated from the disposal panels, or could affect hydrogeological conditions within the disposal system.  Consistent with the containment requirements in 40 CFR § 191.13(a), PAs need not evaluate the effects of the intersection of contaminated material outside the controlled area.

Movement of brine from a pressurized reservoir in the Castile, through a borehole and into thief zones such as the Salado interbeds or the Culebra could result in drilling-induced geochemical changes and altered radionuclide migration rates in these units.

Movement of brine from a pressurized reservoir in the Castile through a borehole into thief zones, such as the Salado interbeds or the Culebra, could cause geochemical changes resulting in altered radionuclide migration rates in these units through their effects on colloid transport and sorption.

The contents of the waste disposal panels provide the main source of colloids in the disposal system.  Thus consistent with the discussion in FEPs H21, H22, and H23 (Section SCR-5.2.1.1, Section SCR-5.2.1.2, and Section SCR-5.2.1.3), colloid transport as a result of drilling-induced flow associated with future boreholes that do not intersect the waste disposal region has been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.

As discussed in FEPs H21, H22, and H23 (Section SCR-5.2.1.1, Section SCR-5.2.1.2, and Section SCR-5.2.1.3), sorption within the Culebra is accounted for in PA calculations.  The sorption model accounts for the effects of changes in sorption in the Culebra as a result of drilling-induced flow associated with boreholes that do not intersect the waste disposal region.

Consistent with the screening discussion in FEPs H21, H22, and H23 (Section SCR-5.2.1.1, Section SCR-5.2.1.2, and Section SCR-5.2.1.3), the effects of changes in sorption in the Dewey Lake within the controlled area as a result of drilling-induced flow associated with boreholes that do not intersect the waste disposal region have been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.  Sorption within other geological units of the disposal system has been eliminated from PA calculations on the basis of beneficial consequence to the performance of the disposal system.

In summary, the effects of drilling-induced geochemical changesthat occur within the controlled area as a result of HCN and future drilling-induced flow are accounted for in PA calculations.  Those that occur outside the controlled area have been eliminated from PA calculations.

HCN Groundwater Extraction and Oil and Gas Extraction outside the controlled area has been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.  Groundwater Extraction and Oil and Gas Extraction through future boreholes has been eliminated from PA calculations on regulatory grounds.

The screening argument for this FEP has been updated with new information relating to a new water well used for ranching purposes near WIPP.  No change to the screening decisions is merited.

The extraction of fluid could alter fluid-flow patterns in the target horizons, or in overlying units as a result of a failed borehole casing.  Also, the removal of confined fluid from oil- or gas-bearing units can cause compaction in some geologic settings, potentially resulting in subvertical fracturing and surface subsidence.

As discussed in FEPs H25 through H36, water, oil, and gas production are the only activities involving fluid extraction through boreholes that have taken place or are currently taking place in the vicinity of the WIPP.  These activities are expected to continue in the vicinity of the WIPP in the near future.

Groundwater extraction outside the controlled area from formations above the Salado could affect groundwater flow.  The Dewey Lake contains a productive zone of saturation south of the WIPP site.  Several wells operated by the J.C. Mills Ranch south of the WIPP produce water from the Dewey Lake to supply livestock (see the CCA, Chapter 2.0, Section 2.2.1.4.2.1).  Water has also been extracted from the Culebra at the Engle Well approximately 9.66 km (6 mi) south of the controlled area to provide water for livestock.  In addition, a new water well was drilled in 2007 at the Sandia National Laboratories (SNL)-14 wellpad to provide livestock water for the Mills ranch.  This well is approximately 3,000 ft (0.9 km) from the WIPP site boundary.

If contaminated water intersects a well while it is producing, then contaminants could be pumped to the surface.  Consistent with the containment requirements in section 191.13(a), PAs need not evaluate radiation doses that might result from such an event.  However, compliance assessments must include any such events in dose calculations for evaluating compliance with the individual protection requirements in section 191.15.  As discussed in the CCA, Chapter 8.0, under undisturbed conditions, there are no calculated radionuclide releases to units containing producing wells.

Pumping from wells at the J.C. Mills Ranch may have resulted in reductions in hydraulic head in the Dewey Lake within southern regions of the controlled area, leading to increased hydraulic head gradients.  However, these changes in the groundwater flow conditions in the Dewey Lake will have no significant effects on the performance of the disposal system, primarily because of the sorptive capacity of the Dewey Lake (see the CCA, Chapter 6.0, Section 6.4.6.6).  Retardation of any radionuclides that enter the Dewey Lake will be such that no radionuclides will migrate through the Dewey Lake to the accessible environment within the 10,000-yr regulatory period.

The effects of groundwater extraction from the Culebra from a well 9.66 km (6 mi) south of the controlled area have been evaluated by Wallace (1996b), using an analytical solution for Darcian fluid flow in a continuous porous medium. Wallace (1996b) showed that such a well pumping at about 0.5 gallon (gal) (1.9 liters [L]) per minute for 10,000 years will induce a hydraulic head gradient across the controlled area of about 4 ´ 10-5.  The hydraulic head gradient across the controlled area currently ranges from between 0.001 to 0.007.  Therefore, pumping from the Engle Well will have only minor effects on the hydraulic head gradient within the controlled area even if pumping were to continue for 10,000 years.  Thus the effects of HCN groundwater extraction outside the controlled area have been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.

Oil and gas extraction outside the controlled area could affect the hydrology of the disposal system.  However, the horizons that act as oil and gas reservoirs are sufficiently below the repository for changes in fluid-flow patterns to be of low consequence, unless there is fluid leakage through a failed borehole casing.  Also, oil and gas extraction horizons in the Delaware Basin are well-lithified rigid strata, so oil and gas extraction is not likely to result in compaction and subsidence (Brausch et al. 1982, pp. 52, 61).  Furthermore, the plasticity of the salt formations in the Delaware Basin will limit the extent of any fracturing caused by compaction of underlying units.  Thus, neither the extraction of gas from reservoirs in the Morrow Formation (some 4,200 m (14,000 ft) below the surface), nor extraction of oil from the shallower units within the Delaware Mountain Group (about 1,250 to 2,450 m (about 4,000 to 8,000 ft) below the surface) will lead to compaction and subsidence.  In summary, historical, current, and near-future oil and gas extraction outside the controlled area has been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.

Consistent with section 194.33(d), PAs need not analyze the effects of techniques used for resource recovery subsequent to the drilling of a future borehole.  Therefore, groundwater extraction and oil and gas extraction through future boreholes have been eliminated from PA calculations on regulatory grounds.

The hydrological effects of HCN fluid injection (Liquid Waste Disposal, Enhanced Oil and Gas Production, and Hydrocarbon Storage) through boreholes outside the controlled area have been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.  Liquid Waste Disposal, Enhanced Oil and Gas Production, and Hydrocarbon Storage in the future have been eliminated from PA calculations based on low consequence.

These FEPs are specific to activities outside the WIPP boundary, although past descriptions have sometimes confused these activities with possible events occurring inside the WIPP boundary, or IB.  Section 194.33(d) excludes activities subsequent to drilling the borehole from further consideration in PA.  It has historically been understood that this exclusion implicitly applies to activities within the WIPP boundary, and not those outside the boundary, or OB.  Therefore, three new FEPs have been created to address analogous IB activities (see Section SCR-5.2.1.7, FEPs H60, Liquid Disposal–IB; H61 Enhanced Oil and Gas Production–IB; and H62 Hydrocarbon Storage–IB).

Recent monitoring activities have identified a salt water disposal well that had hardware failure resulting in migration of the injected fluid away from the wellbore in a shallow freshwater producing zone.  This leak may have persisted up to 22 months, based on inspection and test records on file with the New Mexico Oil Conservation Division.  Once the failure was identified, the well was repaired and returned to service.  Details of this event are discussed in Hall (2008).

Fluid injection modeling conducted since the CCA has demonstrated that injection of fluids will not have a significant effect upon the WIPP’s ability to contain radioactive materials (Stoelzel and Swift 1997).  Conservative assumptions used by Stoelzel and Swift include a leaking well that persists for many years (150) with pressures above maximum allowable permitted pressures in the area.  Therefore, current modeling conservatively bounds the effects of the recent injection well failure mentioned above.  Neither liquid waste disposal nor waterflooding conducted in wells outside the controlled area have the potential to affect the disposal system in any significant way.

The injection of fluids could alter fluid-flow patterns in the target horizons or, if there is accidental leakage through a borehole casing, in any other intersected hydraulically conductive zone.  Injection of fluids through a leaking borehole could also result in geochemical changes and altered radionuclide migration rates in the thief units.

The only historical and current activities involving fluid injection through boreholes in the Delaware Basin are enhanced oil and gas production (waterflooding or carbon dioxide (CO2) injection), hydrocarbon storage (gas reinjection), and liquid waste disposal (byproducts from oil and gas production).  These fluid injection activities are expected to continue in the vicinity of the WIPP in the near future.

Hydraulic fracturing of oil- or gas-bearing units is currently used to improve the performance of hydrocarbon reservoirs in the Delaware Basin.  Fracturing is induced during a short period of high-pressure fluid injection, resulting in increased hydraulic conductivity near the borehole.  Normally, this controlled fracturing is confined to the pay zone and is unlikely to affect overlying strata.

Secondary production techniques, such as waterflooding, that are used to maintain reservoir pressure and displace oil are currently employed in hydrocarbon reservoirs in the Delaware Basin (Brausch et al. 1982, pp. 29-30).  Tertiary recovery techniques, such as CO2 miscible flooding, have been implemented with limited success in the Delaware Basin, but CO2 miscible flooding is not an attractive recovery method for reservoirs near the WIPP (Melzer 2008).  Even if CO2 flooding were to occur, the effects, if any, would be very similar to those associated with waterflooding.

Reinjection of gas for storage currently takes place at one location in the Delaware Basin in a depleted gas field in the Morrow Formation at the Washington Ranch near Carlsbad Caverns (Burton et al. 1993, pp. 66-67; the CRA-2004, Appendix DATA, Attachment A).  This field is too far from the WIPP site to have any effect on WIPP groundwaters under any circumstances.  Disposal of liquid by-products from oil and gas production involves injection of fluid into depleted reservoirs.  Such fluid injection techniques result in repressurization of the depleted target reservoir and mitigates any effects of fluid withdrawal.

The most significant effects of fluid injection would arise from substantial and uncontrolled fluid leakage through a failed borehole casing.  The highly saline environment of some units can promote rapid corrosion of well casings and may result in fluid loss from boreholes.

The Vacuum Field (located in the Capitan Reef, some 30 km [20 mi] northeast of the WIPP site) and the Rhodes-Yates Field (located in the back reef of the Capitan, some 70 km (45 mi) southeast of the WIPP site) have been waterflooded for 40 years with confirmed leaking wells, which have resulted in brine entering the Salado and other formations above the Salado (see, for example, Silva 1994, pp. 67-68).  Currently, saltwater disposal takes place in the vicinity of the WIPP into formations below the Castile.  However, leakages from saltwater disposal wells or waterflood wells in the near future in the vicinity of the WIPP are unlikely to occur because of the following:

·       There are significant differences between the geology and lithology in the vicinity of the disposal system and that of the Vacuum and Rhodes-Yates Fields.  The WIPP is located in the Delaware Basin in a fore-reef environment, where a thick zone of anhydrite and halite (the Castile) exists.  In the vicinity of the WIPP, oil is produced from the Brushy Canyon Formation at depths greater than 2,100 m (7,000 ft).  By contrast, the Castile is not present at either the Vacuum or the Rhodes-Yates Field, which lie outside the Delaware Basin.  Oil production at the Vacuum Field is from the San Andres and Grayburg Formations at depths of approximately 1,400 m (4,500 ft), and oil production at the Rhodes-Yates Field is from the Yates and Seven Rivers Formations at depths of approximately 900 m (3,000 ft).  Waterflooding at the Rhodes-Yates Field involves injection into a zone only 60 m (200 ft) below the Salado.  There are more potential thief zones below the Salado near the WIPP than at the Rhodes-Yates or Vacuum Fields; the Salado in the vicinity of the WIPP is therefore less likely to receive any fluid that leaks from an injection borehole.  Additionally, the oil pools in the vicinity of the WIPP are characterized by channel sands with thin net pay zones, low permeabilities, high irreducible water saturations, and high residual oil saturations.  Therefore, waterflooding of oil fields in the vicinity of the WIPP on the scale of that undertaken in the Vacuum or the Rhodes-Yates Field is unlikely.

·       New Mexico state regulations require the emplacement of a salt isolation casing string for all wells drilled in the potash enclave, which includes the WIPP area, to reduce the possibility of petroleum wells leaking into the Salado.  Also, injection pressures are not allowed to exceed the pressure at which the rocks fracture.  The injection pressure gradient must be kept below 4.5 ´ 103 pascals per meter above hydrostatic if fracture pressures are unknown.  Such controls on fluid injection pressures limit the potential magnitude of any leakages from injection boreholes.

·       Recent improvements in well completion practices and reservoir operations management have reduced the occurrences of leakages from injection wells.  For example, injection pressures during waterflooding are typically kept below about 23 ´ 103 pascals per meter to avoid fracture initiation.  Also, wells are currently completed using cemented and perforated casing, rather than the open-hole completions used in the early Rhodes-Yates wells.  A recent report (Hall et al. 2008) concludes that injection well operations near the WIPP have a low failure rate, and that failures are remedied as soon as possible after identification.

Any injection well leakages that do occur in the vicinity of the WIPP in the near future are more likely to be associated with liquid waste disposal than waterflooding.  Disposal typically involves fluid injection though old and potentially corroded well casings and does not include monitoring to the same extent as waterflooding.  Such fluid injection could affect the performance of the disposal system if sufficient fluid leaked into the Salado interbeds to affect the rate of brine flow into the waste disposal panels.

Stoelzel and O’Brien (1996) evaluated the potential effects on the disposal system of leakage from a hypothetical salt water disposal borehole near the WIPP.  Stoelzel and O’Brien (1996) used the two-dimensional BRAGFLO model (vertical north-south cross-section) to simulate saltwater disposal to the north and to the south of the disposal system.  The disposal system model included the waste disposal region, the marker beds (MBs) and anhydrite intervals near the excavation horizon, and the rock strata associated with local oil and gas developments.  A worst-case simulation was run using high values of borehole and anhydrite permeability and a low value of halite permeability to encourage flow to the disposal panels via the anhydrite.  The boreholes were assumed to be plugged immediately above the Salado (consistent with the plugging configurations described in the CCA, Chapter 6.0, Section 6.4.7.2).  Saltwater disposal into the Upper Bell Canyon was simulated, with annular leakage through the Salado.  A total of approximately 7 ´ 105 m3 (2.47 ´ 107 ft3) of brine was injected through the boreholes during a 50-year simulated disposal period.  In this time, approximately 50 m3 (1,765.5 ft3) of brine entered the anhydrite interval at the horizon of the waste disposal region.  For the next 200 years, the boreholes were assumed to be abandoned (with open-hole permeabilities of 1 ´ 10-9 square meters (m2) (4 ´ 10-8 in.2)).  Cement plugs (of permeability 1 ´ 10-17 m2 (4 ´ 10-16 in.2)) were assumed to be placed at the injection interval and at the top of the Salado.  Subsequently, the boreholes were prescribed the permeability of silty sand (see the CCA, Chapter 6.0, Section 6.4.7.2), and the simulation was continued until the end of the 10,000-yr regulatory period.  During this period, approximately 400 m3 (14,124 ft3) of brine entered the waste disposal region from the anhydrite interval.  This value of cumulative brine inflow is within the bounds of the values generated by PA calculations for the UP scenario.  During the disposal well simulation, leakage from the injection boreholes would have had no significant effect on the inflow rate at the waste panels.

Stoelzel and Swift (1997) expanded on Stoelzel and O’Brien’s (1996) work by considering injection for a longer period of time (up to 150 years) and into deeper horizons at higher pressures.  They developed two computational models (a modified cross-sectional model and an axisymmetric radial model) that are alternatives to the cross-sectional model used by Stoelzel and O’Brien (1996).  Rather than repeat the conservative and bounding approach used by Stoelzel and O’Brien (1996), Stoelzel and Swift (1997) focused on reasonable and realistic conditions for most aspects of the modeling, including setting parameters that were sampled in the CCA at their median values.  Model results indicate that, for the cases considered, the largest volume of brine entering MB 139 (the primary pathway to the WIPP) from the borehole is approximately 1,500 m3 (52,974 ft3), which is a small enough volume that it would not affect Stoelzel and O’Brien’s (1996) conclusion even if it somehow all reached the WIPP.  Other cases showed from 0 to 600 m3 (21,190 ft3) of brine entering MB 139 from the injection well.  In all cases, high-permeability fractures created in the Castile and Salado anhydrite layers by the modeled injection pressures were restricted to less than 400 m (1,312 ft) from the wellbore, and did not extend more than 250 m in MB 138 and MB 139.

No flow entered MB 139, nor was fracturing of the unit calculated to occur away from the borehole, in cases in which leaks in the cement sheath had permeabilities of 10-12.5 m2 (corresponding to the median value used to characterize fully degraded boreholes in the CCA) or lower.  The cases modeled in which flow entered MB 139 from the borehole and fracturing occurred away from the borehole required injection pressures conservatively higher than any currently in use near the WIPP and either 150 years of leakage through a fully degraded cement sheath or 10 years of simultaneous tubing and casing leaks from a waterflood operation.  These conditions are not likely to occur in the future.  If leaks like these do occur from brine injection near the WIPP, however, results of the Stoelzel and Swift (1997) modeling study indicate that they will not affect the performance of the repository.

Thus the hydraulic effects of leakage through HCN boreholes outside the controlled area have been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.

Leakage through a failed borehole casing during a fluid injection operation in the vicinity of the WIPP could alter fluid density in the affected unit, which could result in changes in fluid flow rates and directions within the disposal system.  Disposal of oil and gas production byproducts through boreholes could increase fluid densities in transmissive units affected by leakage in the casing.  Operations such as waterflooding use fluids derived from the target reservoir, or fluids with a similar composition, to avoid scaling and other reactions.  Therefore, the effects of leakage from waterflood boreholes would be similar to leakage from disposal wells.

Denser fluids have a tendency to sink relative to less dense fluids, and, if the hydrogeological unit concerned has a dip, there will be a tendency for the dense fluid to travel in the downdip direction.  If this direction is the same as the direction of the groundwater pressure gradient, there would be an increase in flow velocity, and conversely, if the downdip direction is opposed to the direction of the groundwater pressure gradient, there would be a decrease in flow velocity.  In general terms, taking account of density-related flow will cause a rotation of the flow vector towards the downdip direction that is dependent on the density contrast and the dip.

Wilmot and Galson (1996) showed that brine density changes in the Culebra resulting from leakage through an injection borehole outside the controlled area will not affect fluid flow in the Culebra significantly.  Potash mining activities assumed on the basis of regulatory criteria to occur in the near future outside the controlled area will have a more significant effect on modeled Culebra hydrology.  The distribution of existing leases suggests that near-future mining will take place to the north, west, and south of the controlled area (see the CCA, Chapter 2.0, Section 2.3.1.1).  The effects of such potash mining are accounted for in calculations of UP of the disposal system (through an increase in the transmissivity of the Culebra above the mined region, as discussed in FEPs H37, H38, and H39 [Section SCR-5.2.2.1, Section SCR-5.2.2.2, and Section SCR-5.2.3.1]).  Groundwater modeling that accounts for potash mining shows a change in the fluid pressure distribution and a consequent shift of flow directions towards the west in the Culebra within the controlled area (Wallace 1996c).  A localized increase in fluid density in the Culebra resulting from leakage from an injection borehole would rotate the flow vector towards the downdip direction (towards the east).

Wilmot and Galson (1996) compared the relative magnitudes of the freshwater head gradient and the gravitational gradient and showed that the density effect is of low consequence to the performance of the disposal system.  According to Darcy’s Law, flow in an isotropic porous medium is governed by the gradient of fluid pressure and a gravitational term

                                                                                                          (SCR.7)

where

       v   =  Darcy velocity vector                        (m s-1)

       k   =  intrinsic permeability                        (m2)

       m   =  fluid viscosity                                    (Pa s)

    Ñp   =  gradient of fluid pressure                   (Pa m-1)

       r   =  fluid density                                       (kg m-3)

       g   =  gravitational acceleration vector       (m s-2)

The relationship between the gravity-driven flow component and the pressure-driven component can be shown by expressing the velocity vector in terms of a freshwater head gradient and a density-related elevation gradient

                                                                                              (SCR.8)

where

      K   =  hydraulic conductivity (m s-1)

   ÑHf   =  gradient of freshwater head

    Δρ   =  difference between actual fluid
                 density and reference fluid density (kg m-3)

      ρf   =  density of freshwater (kg m-3)

    ÑE   =  gradient of elevation

Davies (1989, p. 28) defined a driving force ratio (DFR) to assess the potential significance of the density gradient

                                                                                                            (SCR.9)

and concluded that a DFR of 0.5 can be considered an approximate threshold at which density-related gravity effects may become significant (Davies 1989, p. 28).

The dip of the Culebra in the vicinity of the WIPP is about 0.44 degrees or 8 m/km (26 ft/mi) to the east (Davies 1989, p. 42).  According to Davies (1989, pp. 47–48), freshwater head gradients in the Culebra between the waste panels and the southwestern and western boundaries of the accessible environment range from 4 m/km (13 ft/mi) to 7 m/km (23 ft/mi).  Only small changes in gradient arise from the calculated effects of near-future mining.  Culebra brines have densities ranging from 998 to 1,158 kilograms per cubic meter (kg/m3) (998 to 1,158 parts per million [ppm]) (Cauffman et al. 1990, Table E1.b).  Assuming the density of fluid leaking from a waterflood borehole or a disposal well to be 1,215 kg/m3 (1,215 ppm) (a conservative high value similar to the density of Castile brine [Popielak et al. 1983, Table C-2]) leads to a DFR of between 0.07 and 0.43.  These values of the DFR show that density-related effects caused by leakage of brine into the Culebra during fluid injection operations are not significant.

In summary, the effects of HCN fluid injection (liquid waste disposal, enhanced oil and gas production, and hydrocarbon storage) through boreholes outside the controlled area have been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.

Injection of fluids through a leaking borehole could affect the geochemical conditions in thief zones, such as the Salado interbeds or the Culebra.  Such fluid injection-induced geochemical changes could alter radionuclide migration rates within the disposal system in the affected units if they occur sufficiently close to the edge of the controlled area through their effects on colloid transport and sorption.

The majority of fluids injected (for example, during brine disposal) have been extracted locally during production activities.  Because they have been derived locally, their compositions are similar to fluids currently present in the disposal system, and they will have low total colloid concentrations compared to those in the waste disposal panels (see FEPs discussion for H21 through H24, Section SCR-5.2.1.1, Section SCR-5.2.1.2, Section SCR-5.2.1.3, and Section SCR-5.2.1.4).  The repository will remain the main source of colloids in the disposal system.  Therefore, colloid transport as a result of HCN fluid injection has been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.

As discussed in FEPs H21 through H24 (Section SCR-5.2.1.1, Section SCR-5.2.1.2, Section SCR-5.2.1.3, and Section SCR-5.2.1.4), sorption within the Culebra is accounted for in PA calculations.  The sorption model used accounts for the effects of any changes in sorption in the Culebra as a result of leakage through HCN injection boreholes.

Consistent with the screening discussion in FEPs H21 through H24, the effects of changes in sorption in the Dewey Lake within the controlled area as a result of leakage through HCN injection boreholes have been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.  Sorption within other geological units of the disposal system has been eliminated from PA calculations on the basis of beneficial consequence to the performance of the disposal system.

Nonlocally derived fluids could be used during hydraulic fracturing operations.  However, such fluid-injection operations would be carefully controlled to minimize leakage to thief zones.  Therefore, any potential geochemical effects of such leakages have been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.

Consistent with section 194.33(d), PAs need not analyze the effects of techniques used for resource recovery subsequent to the drilling of a future borehole within the site boundary.  Liquid waste disposal (byproducts from oil and gas production), enhanced oil and gas production, and hydrocarbon storage are techniques associated with resource recovery and are expected to continue into the future outside the site boundary.  Analyses have shown that these activities have little consequence on repository performance (Stoelzel and Swift 1997).  Therefore, activities such as liquid waste disposal, enhanced oil and gas production, and hydrocarbon storage outside the site boundary have been eliminated from PA calculations on the basis of low consequence.

The hydrological effects of HCN fluid injection (Liquid Waste Disposal, Enhanced Oil and Gas Production, and Hydrocarbon Storage) through boreholes inside the controlled area have been eliminated from PA calculations on regulatory grounds (section 194.25(a)).  Liquid Waste Disposal, Enhanced Oil and Gas Production, and Hydrocarbon Storage (within the controlled area) in the future have been eliminated from PA calculations on regulatory grounds (section 194.33(d)).

These FEPs are specific to activities inside the WIPP boundary, or IB, although past discussions have sometimes confused these activities with possible events occurring outside the WIPP boundary or OB.  Section 194.33(d) excludes activities subsequent to drilling the borehole from further consideration in PA.  It has historically been understood that this exclusion applies only to IB activities, and not those OB.  Therefore, these FEPs deal specifically with IB activities.  These three new FEPs have been created to address IB activities analogous to FEPs H27, Liquid Disposal-OB; H28 Enhanced Oil and Gas Production-OB; and H29 Hydrocarbon Storage-OB.  The descriptions of the OB activities (H27 – H29, Section SCR-5.2.1.6) have been clarified to be specifically related to activities OB.

The injection of fluids in a borehole within the WIPP boundary could alter fluid-flow patterns in the target horizons or, if there is accidental leakage through a borehole casing, in any other intersected hydraulically conductive zone.  Injection of fluids through a leaking borehole within the WIPP boundary could also result in geochemical changes and altered radionuclide migration rates in the thief units.

Injection of fluids for the purposes of liquid disposal, enhanced oil and gas production, or hydrocarbon storage has not occurred within the WIPP boundary.  Therefore, based on the future states assumption provided by section 194.25(a), it is assumed that such activities will not occur within the near-future time frame, which includes the period of WIPP AICs.  These activities are excluded from PA calculations on regulatory grounds.

The provisions of section 194.33(d) state, “that performance assessments need not analyze the effects of techniques used for resource recovery subsequent to the drilling of the borehole.”  Therefore, the future injection of fluids for the purposes of liquid disposal, enhanced oil and gas production, and hydrocarbon storage within the WIPP boundary have been excluded from PA calculations on regulatory grounds.

Geochemical changes that occur inside the controlled area as a result of fluid flow associated with HCN fluid injection are accounted for in PA calculations.  Geochemical changes resulting from fluid injection in the future inside the controlled area have been eliminated from PA calculations on regulatory grounds.

No new information regarding this FEP has been identified.

The injection of fluids could alter fluid-flow patterns in the target horizons or, if there is accidental leakage through a borehole casing, in any other intersected hydraulically conductive zone.  Injection of fluids through a leaking borehole could also result in geochemical changes and altered radionuclide migration rates in the thief units.

Injection of fluids through a leaking borehole could affect the geochemical conditions in thief zones, such as the Salado interbeds or the Culebra.  Such fluid injection-induced geochemical changes could alter radionuclide migration rates within the disposal system in the affected units if they occur sufficiently close to the edge of the controlled area through their effects on colloid transport and sorption.

The majority of fluids injected (for example, during brine disposal) have been extracted locally during production activities.  Because they have been derived locally, their compositions are similar to fluids currently present in the disposal system, and they will have low total colloid concentrations compared to those in the waste disposal panels (see FEPs H21 through H24, Section SCR-5.2.1.1, Section SCR-5.2.1.2, Section SCR-5.2.1.3, and Section SCR-5.2.1.4).  The repository will remain the main source of colloids in the disposal system.  Therefore, colloid transport as a result of HCN fluid injection has been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.

As discussed in FEPs H21 through H24 (Section SCR-5.2.1.1, Section SCR-5.2.1.2, Section SCR-5.2.1.3, and SCR-5.2.1.4), sorption within the Culebra is accounted for in PA calculations.  The sorption model used accounts for the effects of any changes in sorption in the Culebra as a result of leakage through HCN injection boreholes.

Consistent with the screening discussion in FEPs H21 through H24, the effects of changes in sorption in the Dewey Lake within the controlled area as a result of leakage through HCN injection boreholes have been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.  Sorption within other geological units of the disposal system has been eliminated from PA calculations on the basis of beneficial consequence to the performance of the disposal system.

Nonlocally derived fluids could be used during hydraulic fracturing operations.  However, such fluid injection operations would be carefully controlled to minimize leakage to thief zones.  Therefore, any potential geochemical effects of such leakages have been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.

Consistent with section 194.33(d), PAs need not analyze the effects of techniques used for resource recovery subsequent to the drilling of a future borehole.  Liquid waste disposal (byproducts from oil and gas production), enhanced oil and gas production, and hydrocarbon storage are techniques associated with resource recovery.  Therefore, the use of future boreholes for such activities and fluid injection-induced geochemical changes have been eliminated from PA calculations on regulatory grounds.

The effects of Natural Borehole Fluid Flow through existing or near-future abandoned boreholes, known or unknown, have been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.  Natural Borehole Fluid Flow through a future borehole that intersects a waste panel is accounted for in PA calculations.  The effects of Natural Borehole Fluid Flow through a future borehole that does not intersect the waste-disposal region have been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.

No new information has been identified for this FEP.

Abandoned boreholes could provide pathways for fluid flow and, potentially, contaminant transport between any intersected zones.  For example, such boreholes could provide pathways for vertical flow between transmissive units in the Rustler, or between the Culebra and units below the Salado, which could affect fluid densities, flow rates, and flow directions.

Movement of fluids through abandoned boreholes could result in borehole-induced geochemical changes in the receiving units such as the Salado interbeds or Culebra, and thus alter radionuclide migration rates in these units.

Potentially, boreholes could provide pathways for surface-derived water or groundwater to percolate through low-permeability strata and into formations containing soluble minerals.  Large-scale dissolution through this mechanism could lead to subsidence and to changes in groundwater flow patterns.  Also, fluid flow between hydraulically conductive horizons through a borehole may result in changes in permeability in the affected units through mineral precipitation.

Abandoned water, potash, oil, and gas exploration and production boreholes exist within and outside the controlled area.  Most of these boreholes have been plugged in some way, but some have simply been abandoned.  Over time, even the boreholes that have been plugged may provide hydraulic connections among the units they penetrate as the plugs degrade.  The DOE assumes that records of past and present drilling activities in New Mexico are largely accurate and that evidence of most boreholes would be included in these records.  However, the potential effects of boreholes do not change depending on whether their existence is known, hence flow through undetected boreholes and flow through detected boreholes can be evaluated together.

Fluid flow and radionuclide transport within the Culebra could be affected if deep boreholes result in hydraulic connections between the Culebra and deep, overpressurized or underpressurized units, or if boreholes provide interconnections for flow between shallow units.

Fluid flow and radionuclide transport within the Culebra could be affected if deep boreholes result in hydraulic connections between the Culebra and deep, overpressurized or underpressurized units.  Over the past 80 years, a large number of deep boreholes have been drilled within and around the controlled area (see the CCA, Chapter 6.0, Section 6.4.12.2).  The effects on the performance of the disposal system of long-term hydraulic connections between the Culebra and deep units depends on the locations of the boreholes.  In some cases, changes in the Culebra flow field caused by interconnections with deep units could decrease lateral radionuclide travel times to the accessible environment.

As part of an analysis to determine the impact of such interconnections, Wallace (1996a) gathered information on the pressures, permeabilities, and thicknesses of potential oil- or gas-bearing sedimentary units; such units exist to a depth of about 5,500 m (18,044 ft) in the vicinity of the WIPP.  Of these units, the Atoka, some 4,000 m (13,123 ft) below the land surface, has the highest documented pressure of about 64 megapascals (MPa) (9,600 pounds per square inch [psi]), with permeability of about 2 ´ 10-14 m2 (2.1 ´ 10-13 square feet [ft2]) and thickness of about 210 m (689 ft).  The Strawn, 3,900 m (12,795 ft) below the land surface, has the lowest pressures (35 MPa [5,000 psi], which is lower than hydrostatic) and highest permeability (10-13 m2 [1.1 ´ 10-12 ft2]) of the deep units, with a thickness of about 90 m (295 ft).

PA calculations indicate that the shortest radionuclide travel times to the accessible environment through the Culebra occur when flow in the Culebra in the disposal system is from north to south.  Wallace (1996a) ran the steady-state SECOFL2D model with the PA data that generated the shortest radionuclide travel times (with and without mining in the controlled area) but perturbed the flow field by placing a borehole connecting the Atoka to the Culebra just north of the waste disposal panels and a borehole connecting the Culebra to the Strawn just south of the controlled area.  The borehole locations were selected to coincide with the end points of the fastest flow paths modeled, which represents an unlikely worst-case condition.  Although the Atoka is primarily a gas-bearing unit, Wallace (1996a) assumed that the unit is brine saturated.  This assumption is conservative because it prevents two-phase flow from occurring in the Culebra, which would decrease the water permeability and thereby increase transport times.  It was conservatively assumed that the pressure in the Atoka would not have been depleted by production before the well was plugged and abandoned.  Furthermore, it was conservatively assumed that all flow from the Atoka would enter the Culebra and not intermediate or shallower units, and that flow from the Culebra could somehow enter the Strawn despite intermediate zones having higher pressures than the Culebra.  The fluid flux through each borehole was determined using Darcy’s Law, assuming a borehole hydraulic conductivity of 10-4 m/s (for a permeability of about 10-11 m2 [1.1 ´ 10-10 ft2]) representing silty sand, a borehole radius of 0.25 m (.82 ft), and a fluid pressure in the Culebra of 0.88 MPa (132 psi) at a depth of about 200 m (650 ft).  With these parameters, the Atoka was calculated to transmit water to the Culebra at about 1.4 ´ 10-5 m3/s (0.22 gallons per minute [gpm]), and the Strawn was calculated to receive water from the Culebra at about 1.5 ´ 10-6 m3/s (0.024 gpm).

Travel times through the Culebra to the accessible environment were calculated using the SECOFL2D velocity fields for particles released to the Culebra above the waste panels, assuming no retardation by sorption or diffusion into the rock matrix.  Mean Darcy velocities were then determined from the distance each radionuclide traveled, the time taken to reach the accessible environment, and the effective Culebra porosity.  The results show that, at worst, interconnections between the Culebra and deep units under the unrealistically conservative assumptions listed above could cause less than a twofold increase in the largest mean Darcy velocity expected in the Culebra in the absence of such interconnections.

These effects can be compared to the potential effects of climate change on gradients and flow velocities through the Culebra.  As discussed in the CCA, Chapter 6.0, Section 6.4.9 (and Corbet and Knupp 1996), the maximum effect of a future, wetter climate would be to raise the water table to the ground surface.  This would raise heads and gradients in all units above the Salado.  For the Culebra, the maximum change in gradient was estimated to be about a factor of 2.1.  The effect of climate change is incorporated in compliance calculations through the Climate Index, which is used as a multiplier for Culebra groundwater velocities.  The Climate Index has a bimodal distribution, with the range from 1.00 to 1.25 having a 75% probability, and the range from 1.50 to 2.25 having a 25% probability.  Because implementation of the Climate Index leads to radionuclide releases through the Culebra that are orders of magnitude lower than the regulatory limits, the effects of flow between the Culebra and deeper units through abandoned boreholes can be screened out on the basis of low consequence.

Abandoned boreholes could also provide interconnections for long-term fluid flow between shallow units (overlying the Salado).  Abandoned boreholes could provide pathways for downward flow of water from the Dewey Lake and/or Magenta to the Culebra because the Culebra hydraulic head is lower than the hydraulic heads of these units.  Magenta freshwater heads are as much as 45 m (148 ft) higher than Culebra freshwater heads.  Because the Culebra is generally at least one order of magnitude more transmissive than the Magenta at any location, a connection between the Magenta and Culebra would cause proportionally more drawdown in the Magenta head than rise in the Culebra head.  For example, for a one-order-of-magnitude difference in transmissivity and a 45-m (148-ft) difference in head, the Magenta head would decrease by approximately 40 m (131 ft) while the Culebra head increased by 5 m (16 ft).  This head increase in the Culebra would also be a localized effect, decreasing with radial distance from the leaking borehole.  The primary flow direction in the Culebra across the WIPP site is from north to south, with the Culebra head decreasing by approximately 20 m (66 ft) across this distance.  A 5-m (16-ft) increase in Culebra head at the northern WIPP boundary would, therefore, increase gradients by at most 25%.

The Dewey Lake freshwater head at the WQSP-6 pad is 55 m (180 ft) higher than the Culebra freshwater head.  Leakage from the Dewey Lake could have a greater effect on Culebra head than leakage from the Magenta if the difference in transmissivity between the Dewey Lake and Culebra observed at the WQSP-6 pad, where the Dewey Lake is two orders of magnitude more transmissive than the Culebra (Beauheim and Ruskauff 1998), persists over a wide region.  However, the saturated, highly transmissive zone in the Dewey Lake has only been observed south of the WIPP disposal panels.  A connection between the Dewey Lake and the Culebra south of the panels would tend to decrease the north-south gradient in the Culebra across the site, not increase it.

In any case, leakage of water from overlying units into the Culebra could not increase Culebra heads and gradients as much as might result from climate change, discussed above.  Because implementation of the Climate Index leads to radionuclide releases through the Culebra that are orders of magnitude lower than the regulatory limits, the effects of flow between the Culebra and shallower units through abandoned boreholes can be screened out on the basis of low consequence.

Leakage from historical, current, and near-future abandoned boreholes that penetrate pressurized brine pockets in the Castile could give rise to fluid density changes in affected units. Wilmot and Galson (1996) showed that brine density changes in the Culebra resulting from leakage through an abandoned borehole would not have a significant effect on the Culebra flow field.  A localized increase in fluid density in the Culebra resulting from leakage from an abandoned borehole would rotate the flow vector towards the downdip direction (towards the east).  A comparison of the relative magnitudes of the freshwater head gradient and the gravitational gradient, based on an analysis similar to that presented in Section SCR-5.2.1.6 (FEPs H27, H28, and H29), shows that the density effect is of low consequence to the performance of the disposal system.

The EPA provides criteria for analysis of the consequences of future drilling events in section 194.33(c).  Consistent with these criteria, the DOE assumes that after drilling is complete, the borehole is plugged according to current practice in the Delaware Basin (see the CCA, Chapter 6.0, Section 6.4.7.2).  Degradation of casing and/or plugs may result in connections for fluid flow and, potentially, contaminant transport between connected hydraulically conductive zones.  The long-term consequences of boreholes drilled and abandoned in the future will primarily depend on the location of the borehole and the borehole casing and plugging methods used.

A future borehole that penetrates a Castile brine reservoir could provide a connection for brine flow from the reservoir to the waste panel, thus increasing fluid pressure and brine volume in the waste panel.  Long-term natural borehole fluid flow through such a borehole is accounted for in PA calculations (see the CCA, Chapter 6.0, Section 6.4.8).

Deep, abandoned boreholes that intersect the Salado interbeds near the waste disposal panels could provide pathways for long-term radionuclide transport from the waste panels to the land surface or to overlying units.  The potential significance of such events were assessed by the WIPP PA Department (1991, B-26 to B-27), which examined single-phase flow and transport between the waste panels and a borehole intersecting MB 139 outside the DRZ.  The analysis assumed an in situ pressure of 11 MPa in MB 139, a borehole pressure of 6.5 MPa (975 psi) (hydrostatic) at MB 139, and a constant pressure of 18 MPa (2,700 psi) as a source term in the waste panels representing gas generation.  Also, MB 139 was assigned a permeability of approximately 3 ´ 10-20 m2 (3.2 ´ 10-19 ft2) and a porosity of 0.01%.  The disturbed zone was assumed to exist in MB 139 directly beneath the repository only and was assigned a permeability of 1.0 ´ 10-17 m2 (1.1 ´ 10-16 ft2) and a porosity of 0.055%.  Results showed that the rate of flow through a borehole located just 0.25 m (0.8 ft) outside the DRZ would be more than two orders of magnitude less than the rate of flow through a borehole located within the DRZ because of the contrast in permeability.  Thus any releases of radionuclides to the accessible environment through deep boreholes that do not intersect waste panels would be insignificant compared to the releases that would result from transport through boreholes that intersect waste panels.  Thus radionuclide transport through deep boreholes that do not intersect waste panels has been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.

Fluid flow and radionuclide transport within the Culebra could be affected if future boreholes result in hydraulic connections between the Culebra and either deeper or shallower units.  Over the 10,000-yr regulatory period, a large number of deep boreholes could be drilled within and around the controlled area (see the CCA, Chapter 6.0, Section 6.4.12.2).  The effects on the performance of the disposal system of long-term hydraulic connections between the Culebra and deeper or shallower units would be the same as those discussed above for historic, current, and near-future conditions.  Thus the effects of flow between the Culebra and deeper or shallower units through abandoned future boreholes can be screened out on the basis of low consequence.

A future borehole that intersects a pressurized brine reservoir in the Castile could also provide a source for brine flow to the Culebra in the event of borehole casing leakage, with a consequent localized increase in fluid density in the Culebra.  The effect of such a change in fluid density would be to increase any density-driven component of groundwater flow.  If the downdip direction, along which the density-driven component would be directed, is different from the direction of the groundwater pressure gradient, there would be a slight rotation of the flow vector towards the downdip direction.  The groundwater modeling presented by Davies (1989, p. 50) indicates that a borehole that intersects a pressurized brine pocket and causes a localized increase in fluid density in the Culebra above the waste panels would result in a rotation of the flow vector slightly towards the east.  However, the magnitude of this effect would be small in comparison to the magnitude of the pressure gradient (see screening argument for FEPs H27, H28, and H29, Section SCR-5.2.1.6, where this effect is screened out on the basis of low consequence).

Waste-induced flow through boreholes drilled in the near future has been eliminated from PA calculations on regulatory grounds.  Waste-Induced Borehole Flow through a future borehole that intersects a waste panel are accounted for in PA calculations.

No new information has been identified for this FEP.

Abandoned boreholes could provide pathways for fluid flow and, potentially, contaminant transport between any intersected zones.  For example, such boreholes could provide pathways for vertical flow between transmissive units in the Rustler, or between the Culebra and units below the Salado, which could affect fluid densities, flow rates, and flow directions.

Continued resource exploration and production in the near future will result in the occurrence of many more abandoned boreholes in the vicinity of the controlled area.  Institutional controls will prevent drilling (other than that associated with the WIPP development) from taking place within the controlled area in the near future.  Therefore, no boreholes will intersect the waste disposal region in the near future, and waste-induced borehole flow in the near future has been eliminated from PA calculations on regulatory grounds.

The EPA provides criteria concerning analysis of the consequences of future drilling events in section 194.33(c).  Consistent with these criteria, the DOE assumes that after drilling is complete, the borehole is plugged according to current practice in the Delaware Basin (see the CCA, Chapter 6.0, Section 6.4.7.2).  Degradation of casing and/or plugs may result in connections for fluid flow and, potentially, contaminant transport between connected hydraulically conductive zones.  The long-term consequences of boreholes drilled and abandoned in the future will primarily depend on the location of the borehole and the borehole casing and plugging methods used.

An abandoned future borehole that intersects a waste panel could provide a connection for contaminant transport away from the repository horizon.  If the borehole has degraded casing and/or plugs, and the fluid pressure within the waste panel is sufficient, radionuclides could be transported to the land surface.  Additionally, if brine flows through the borehole to overlying units, such as the Culebra, it may carry dissolved and colloidal actinides that can be transported laterally to the accessible environment by natural groundwater flow in the overlying units.  Long-term waste-induced borehole flow is accounted for in PA calculations (see Appendix PA-2009, Section PA-2.1.4.5).

The effects of Borehole-Induced Solution and Subsidence associated with existing, near-future, and future abandoned boreholes have been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.

No new information has been identified for this FEP.

Potentially, boreholes could provide pathways for surface-derived water or groundwater to percolate through low-permeability strata and into formations containing soluble minerals.  Large-scale dissolution through this mechanism could lead to subsidence and to changes in groundwater flow patterns.  Also, fluid flow between hydraulically conductive horizons through a borehole may result in changes in permeability in the affected units through mineral precipitation.

SCR-5.2.1.11.3.1.1  Borehole-Induced Solution and Subsidence

During the period covered by HCN FEPs, drilling within the land withdrawn for the WIPP will be controlled, and boreholes will be plugged according to existing regulations. Under these circumstances and during this time period, borehole-induced solution and subsidence at WIPP is eliminated from PA calculations on the basis of no consequence to the disposal system.

Outside the area withdrawn for the WIPP, drilling has been regulated, but conditions of historical and existing boreholes are highly variable. Borehole-induced solution and subsidence may occur in these areas, although it is expected to be limited and should not affect the disposal system, as discussed in the following paragraphs.

Three features are required for significant borehole-induced solution and subsidence to occur:  a borehole, an energy gradient to drive unsaturated (with respect to halite) water through the evaporite-bearing formations, and a conduit to allow migration of brine away from the site of dissolution.  Without these features, minor amounts of halite might be dissolved in the immediate vicinity of a borehole, but percolating water would become saturated with respect to halite and stagnant in the bottom of the drillhole, preventing further dissolution.

At, and in the vicinity of, the WIPP site, drillholes penetrating into, but not through, the evaporite-bearing formations have little potential for dissolution. Brines coming from the Salado and Castile, for example, have high total dissolved solids and are likely to precipitate halite, not dissolve more halite during passage through the borehole. Water infiltrating from the surface or near-surface units may not be saturated with halite.  For drillholes with a total depth in halite-bearing formations, there is little potential for dissolution because the halite-bearing units have very low permeability and provide little outlet for the brine created as the infiltrating water fills the drillhole. ERDA-9 is the deepest drillhole in the immediate vicinity of the waste panels at the WIPP; the bottom of the drillhole is in the uppermost Castile, with no known outlet for brine at the bottom.

Drillholes penetrating through the evaporite-bearing formations provide possible pathways for circulation of water. Underlying units in the vicinity of the WIPP site with sufficient potentiometric levels or pressures to reach or move upward through the halite units generally have one of two characteristics:  (1) high-salinity brines, which limit or eliminate the potential for dissolution of evaporites, or (2) are gas producers. Wood et al. (1982) analyzed natural processes of dissolution of the evaporites by water from the underlying Bell Canyon. They concluded that brine removal in the Bell Canyon is slow, limiting the movement of dissolution fronts or the creation of natural collapse features. Existing drillholes that are within the boundaries of the withdrawn land and also penetrate through the evaporites are not located in the immediate vicinity of the waste panels or WIPP workings.

There are three examples in the region that appear to demonstrate the process for borehole-induced solution and subsidence, but the geohydrologic setting and drillhole completions differ from those at or near the WIPP.

An example of borehole-induced solution and subsidence occurred in 1980 about 160 km (100 mi) southeast of the WIPP site (outside the Delaware Basin) at the Wink Sink (Baumgardner et al. 1982; Johnson 1989), where percolation of shallow groundwater through abandoned boreholes, dissolution of the Salado, and subsidence of overlying units led to a surface collapse feature 110 m (360 ft) in width and 34 m (110 ft) deep.  At the Wink Sink, the Salado is underlain by the Tansill, Yates, and Capitan Formations, which contain vugs and solution cavities through which brine could migrate.  Also, the hydraulic head of the Santa Rosa (the uppermost aquifer) is greater than those of the deep aquifers (Tansill, Yates, and Capitan), suggesting downward flow if a connection were established. A second sink (Wink Sink 2) formed in May 2002, near the earlier sink (Johnson et al. 2003). Its origin is similar to the earlier sink.  By February 2003, Wink Sink 2 had enlarged by surface collapse to a length of about 305 m (1,000 ft) and a width of about 198 m (650 ft).

A similar, though smaller, surface collapse occurred in 1998 northwest of Jal, New Mexico (Powers 2000). The most likely cause of collapse appears to be dissolution of Rustler, and possibly Salado, halite as relatively low salinity water from the Capitan Reef circulated through breaks in the casing of a deep water supply well. Much of the annulus behind the casing through the evaporite section was uncemented, and work in the well at one time indicated bent and ruptured casing. The surface collapse occurred quickly, and the sink was initially about 23 m (75 ft) across and a little more than 30 m (100 ft) deep. By 2001, the surface diameter was about 37 m (120 ft), and the sink was filled with collapse debris to about 18 m (60 ft) below the ground level (Powers, in press).

The sinkholes near Wink, Texas and Jal, New Mexico, occurred above the Capitan Reef (which is by definition outside the Delaware Basin), and the low-salinity water and relatively high potentiometric levels of the Capitan Reef appear to be integral parts of the process that formed these sinkholes. They are reviewed as examples of the process of evaporite dissolution and subsidence related to circulation in drillholes. Nevertheless, the factors of significant low salinity water and high potentiometric levels in units below the evaporites do not appear to apply at the WIPP site.

Beauheim (1986) considered the direction of natural fluid flow through boreholes in the vicinity of the WIPP.  Beauheim (1986, p. 72) examined hydraulic heads measured using drill stem tests in the Bell Canyon and the Culebra at well DOE-2 and concluded that the direction of flow in a cased borehole open only to the Bell Canyon and the Culebra would be upward. Bell Canyon waters in the vicinity of the WIPP site are saline brines (e.g., Lambert 1978; Beauheim et al. 1983; Mercer et al. 1987), limiting the potential for dissolution of the overlying evaporites. However, dissolution of halite in the Castile and the Salado would increase the relative density of the fluid in an open borehole, causing a reduction in the rate of upward flow.  The direction of borehole fluid flow could potentially reverse, but such a flow could be sustained only if sufficient driving pressure, porosity, and permeability exist for fluid to flow laterally within the Bell Canyon.  A further potential sink for Salado-derived brine is the Capitan Limestone.  However, the subsurface extent of the Capitan Reef is approximately 16 km (10 mi) from the WIPP at its closest point, and this unit will not provide a sink for brine derived from boreholes in the vicinity of the controlled area.  A similar screening argument is made for natural deep dissolution in the vicinity of the WIPP (see N16 and N18, Section SCR-4.1.5.1 and Section SCR-4.1.5.2).

The effects of borehole-induced solution and subsidence through a waste panel are considered below. The principal effects of borehole-induced solution and subsidence in the remaining parts of the disposal system should be to change the hydraulic properties of the Culebra and other rocks in the system. The features are local (limited lateral dimensions) and commonly nearly circular. If subsidence occurs along the expected travel path and the transmissivity of the Culebra is increased, as in the calculations conducted by Wallace (1996c), the travel times should increase. If the transmissivity along the expected flow path decreased locally as a result of such a feature, the flow path should be lengthened by travel around the feature. Thus the effects of borehole-induced solution and subsidence around existing abandoned boreholes, and boreholes drilled and abandoned in the near-future, have been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.

The EPA provides criteria concerning analysis of the consequences of future drilling events in section 194.33(c).  Consistent with these criteria, the DOE assumes that after drilling is complete the borehole is plugged according to current practice in the Delaware Basin (see Appendix PA-2009, Section PA-2.1.4.5).  Degradation of casing and/or plugs may result in connections for fluid flow and, potentially, contaminant transport between connected hydraulically conductive zones.  The long-term consequences of boreholes drilled and abandoned in the future will primarily depend on the location of the borehole and the borehole casing and plugging methods used.

SCR-5.2.1.11.3.2.1  Borehole-Induced Solution and Subsidence

Future boreholes that do not intersect the WIPP excavation do not differ in long-term behavior or consequences from existing boreholes, and can be eliminated from PA on the basis of low consequence to the performance of the disposal system.

The condition of more apparent concern is a future borehole that intersects the WIPP excavation. Seals and casings are assumed to degrade, connecting the excavation to various units. For a drillhole intersecting the excavation, but not connecting to a brine reservoir or to formations below the evaporites, downward flow is limited by the open volume of the disposal room(s), which is dependent with time, gas generation, or brine inflow to the disposal system from the Salado.

Maximum dissolution, and maximum increase in borehole diameter, will occur at the top of the Salado; dissolution will decrease with depth as the percolating water becomes salt saturated.  Eventually, degraded casing and concrete plug products, clays, and other materials will fill the borehole.  Long-term flow through a borehole that intersects a waste panel is accounted for in DP calculations by assuming that the borehole is eventually filled by such materials, which have the properties of a silty sand (see Appendix PA-2009, Section PA-2.1.4.5).  However, these calculations assume that the borehole diameter does not increase with time. Under the conditions assumed in the CCA for an E2 drilling event at 1,000 years, about 1,000 m3 (35,316 ft3) would be dissolved from the lower Rustler and upper Salado.  If the dissolved area is approximately cylindrical or conical around the borehole, and the collapse/subsidence propagates upward as occurred in breccia pipes (e.g., Snyder and Gard 1982), the diameter of the collapsed or subsided area through the Culebra and other units would be a few tens of meters across.  Changes in hydraulic parameters for this small zone should slow travel times for any hypothesized radionuclide release, as discussed for HCN occurrences.  This does not change the argument for low consequence due to borehole-induced solution and subsidence for these circumstances.

If a drillhole through a waste panel and into deeper evaporites intercepts a Castile brine reservoir, the brine has little or no capability of dissolving additional halite. The Castile brine flow is considered elsewhere as part of DP. There is, however, no Borehole-Induced Solution and Subsidence under this circumstance, and therefore there is no effect on performance because of this EP.

If a borehole intercepts a waste panel and also interconnects with formations below the evaporite section, fluid flow up or down is determined by several conditions and may change over a period of time (e.g., as dissolution increases the fluid density in the borehole).  Fluid flow downward is not a concern for performance, as fluid velocities in units such as the Bell Canyon are slow and should not be of concern for performance (Wilson et al., 1996).  As with boreholes considered for HCN, the local change in hydraulic parameters, if it occurs along the expected flow path, would be expected to cause little change in travel time and should increase the travel time.

In summary, the effects of borehole-induced solution and subsidence around future abandoned boreholes have been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.

The effects of Borehole-Induced Mineralization, associated with existing, near-future, and future abandoned boreholes, have been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.

No new information has been identified for this FEP.

Abandoned boreholes could provide pathways for fluid flow and, potentially, contaminant transport between any intersected zones.  For example, such boreholes could provide pathways for vertical flow between transmissive units in the Rustler, or between the Culebra and units below the Salado, which could affect fluid densities, flow rates, and flow directions.

Movement of fluids through abandoned boreholes could result in borehole-induced geochemical changes in the receiving units, such as the Salado interbeds or Culebra, and thus alter radionuclide migration rates in these units.

Potentially, boreholes could provide pathways for surface-derived water or groundwater to percolate through low-permeability strata and into formations containing soluble minerals.  Large-scale dissolution through this mechanism could lead to subsidence and to changes in groundwater flow patterns.  Also, fluid flow between hydraulically conductive horizons through a borehole may result in changes in permeability in the affected units through mineral precipitation.

Fluid flow between hydraulically conductive horizons through a borehole may result in changes in permeability in the affected units through mineral precipitation.  For example:

·       Limited calcite precipitation may occur as the waters mix in the Culebra immediately surrounding the borehole, and calcite dissolution may occur as the brines migrate away from the borehole as a result of variations in water chemistry along the flow path.

·       Gypsum may be dissolved as the waters mix in the Culebra immediately surrounding the borehole but may precipitate as the waters migrate through the Culebra.

The effects of these mass transfer processes on groundwater flow depend on the original permeability structure of the Culebra rocks and the location of the mass transfer.  The volumes of minerals that may precipitate or dissolve in the Culebra as a result of the injection of Castile or Salado brine through a borehole will not affect the existing spatial variability in the permeability field significantly.

Predicted radionuclide transport rates in the Culebra assume that the dolomite matrix is diffusively accessed by the contaminants.  The possible inhibition of matrix diffusion by secondary mineral precipitation on fracture walls as a result of mixing between brines and Culebra porewater was addressed by Wang (1998).  Wang showed that the volume of secondary minerals precipitated because of this mechanism was too small to significantly affect matrix porosity and accessibility.

Consequently, the effects of borehole-induced mineralization on permeability and groundwater flow within the Culebra, as a result of brines introduced via any existing abandoned boreholes and boreholes drilled and abandoned in the near future, have been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.

The EPA provides criteria concerning analysis of the consequences of future drilling events in section 194.33(c).  Consistent with these criteria, the DOE assumes that after drilling is complete the borehole is plugged according to current practice in the Delaware Basin (see Appendix PA-2009, Section PA-2.1.4.5).  Degradation of casing and/or plugs may result in connections for fluid flow and, potentially, contaminant transport between connected hydraulically conductive zones.  The long-term consequences of boreholes drilled and abandoned in the future will primarily depend on the location of the borehole and the borehole casing and plugging methods used.

Fluid flow between hydraulically conductive horizons through a future borehole may result in changes in permeability in the affected units through mineral precipitation.  However, the effects of mineral precipitation as a result of flow through a future borehole in the controlled area will be similar to the effects of mineral precipitation as a result of flow through an existing or near-future borehole (see FEP H32, Section SCR-5.2.1.10).  Thus borehole-induced mineralization associated with flow through a future borehole has been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.

Geochemical changes that occur inside the controlled area as a result of long-term flow associated with HCN and future abandoned boreholes are accounted for in PA calculations.

No new information has been identified for this FEP.

Abandoned boreholes could provide pathways for fluid flow and, potentially, contaminant transport between any intersected zones.  For example, such boreholes could provide pathways for vertical flow between transmissive units in the Rustler, or between the Culebra and units below the Salado, which could affect fluid densities, flow rates, and flow directions.

Movement of fluids through abandoned boreholes could result in borehole-induced geochemical changes in the receiving units such as the Salado interbeds or Culebra, and thus alter radionuclide migration rates in these units.

Movement of fluids through abandoned boreholes could result in borehole-induced geochemical changes in the receiving units such as the Salado interbeds or Culebra.  Such geochemical changes could alter radionuclide migration rates within the disposal system in the affected units if they occur sufficiently close to the edge of the controlled area, or if they occur as a result of flow through existing boreholes within the controlled area through their effects on colloid transport and sorption.

The contents of the waste disposal panels provide the main source of colloids in the disposal system.  Thus, consistent with the discussion in Section SCR-5.2.1.4 (Borehole-Induced Geochemical Changes [H24]), colloid transport as a result of flow through existing and near-future abandoned boreholes has been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.

As discussed in H24, sorption within the Culebra is accounted for in PA calculations.  The sorption model used accounts for the effects of changes in sorption in the Culebra as a result of flow through existing and near-future abandoned boreholes.

Consistent with the screening discussion in Section SCR-5.2.1.4, the effects of changes in sorption in the Dewey Lake inside the controlled area as a result of flow through existing and near-future abandoned boreholes have been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.  Sorption within other geological units of the disposal system has been eliminated from PA calculations on the basis of beneficial consequence to the performance of the disposal system.

The EPA provides criteria concerning analysis of the consequences of future drilling events in section 194.33(c).  Consistent with these criteria, the DOE assumes that after drilling is complete the borehole is plugged according to current practice in the Delaware Basin (see Appendix PA-2009, Section PA-2.1.4.5).  Degradation of casing and/or plugs may result in connections for fluid flow and, potentially, contaminant transport between connected hydraulically conductive zones.  The long-term consequences of boreholes drilled and abandoned in the future will primarily depend on the location of the borehole and the borehole casing and plugging methods used.

Movement of fluids through abandoned boreholes could result in borehole-induced geochemical changes in the receiving units, such as the Salado interbeds or Culebra.  Such geochemical changes could alter radionuclide migration rates within the disposal system in the affected units through their effects on colloid transport and sorption.

The waste disposal panels provide the main source of colloids in the disposal system.  Colloid transport within the Culebra as a result of long-term flow associated with future abandoned boreholes that intersect the waste disposal region are accounted for in PA calculations, as described in the CCA, Chapter 6.0, Section 6.4.3.6 and Section 6.4.6.2.1.  Consistent with the discussion in Section SCR-5.2.1.4, colloid transport as a result of flow through future abandoned boreholes that do not intersect the waste disposal region has been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.  The Culebra is the most transmissive unit in the disposal system and it is the most likely unit through which significant radionuclide transport could occur.  Therefore, colloid transport in units other than the Culebra, as a result of flow through future abandoned boreholes, has been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.

As discussed in Section SCR-5.2.1.4, sorption within the Culebra is accounted for in PA calculations.  The sorption model accounts for the effects of changes in sorption in the Culebra as a result of flow through future abandoned boreholes.

Consistent with the screening discussion in Section SCR-5.2.1.4, the effects of changes in sorption in the Dewey Lake within the controlled area as a result of flow through future abandoned boreholes have been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.  Sorption within other geological units of the disposal system has been eliminated from PA calculations on the basis of beneficial consequence to the performance of the disposal system.

Changes in Groundwater Flow due to Mining (HCN and future) are accounted for in PA calculations.

No new information has been identified for this FEP.

Excavation activities may result in hydrological disturbances of the disposal system.  Subsidence associated with excavations may affect groundwater flow patterns through increased hydraulic conductivity within and between units.  Fluid flow associated with excavation activities may also result in changes in brine density and geochemistry in the disposal system.

Currently, potash mining is the only excavation activity currently taking place in the vicinity of the WIPP that could affect hydrogeological or geochemical conditions in the disposal system.  Potash is mined in the region east of Carlsbad and up to 5 km (3.1 mi) from the boundaries of the controlled area.  Mining of the McNutt Potash Zone in the Salado is expected to continue in the vicinity of the WIPP (see the CCA, Chapter 2.0, Section 2.3.1.1): the DOE assumes that all economically recoverable potash in the vicinity of the WIPP (outside the controlled area) will be extracted in the near future.

Potash mining in the Delaware Basin typically involves constructing vertical shafts to the elevation of the ore zone and then extracting the minerals in an excavation that follows the trend of the ore body.  Potash has been extracted using conventional room-and-pillar mining, secondary mining where pillars are removed, and modified long-wall mining methods.  Mining techniques used include drilling and blasting (used for mining langbeinite) and continuous mining (commonly used for mining sylvite).  The DOE (Westinghouse 1994, pp. 2-17 to 2-19) reported investigations of subsidence associated with potash mining operations located near the WIPP.  The reported maximum total subsidence at potash mines is about 1.5 m (5 ft), representing up to 66% of initial excavation height, with an observed angle of draw from the vertical at the edge of the excavation of 58 degrees.  The DOE (Westinghouse 1994 pp. 2-22 to 2-23) found no evidence that subsidence over local potash mines had caused fracturing sufficient to connect the mining horizon to water-bearing units or the surface.  However, subsidence and fracturing associated with mining in the McNutt in the vicinity of the WIPP may allow increased recharge to the Rustler units and affect the lateral hydraulic conductivity of overlying units, such as the Culebra, which could influence the direction and magnitude of fluid flow within the disposal system.  Such changes in groundwater flow due to mining are accounted for in calculations of UP of the disposal system.  The effects of any increased recharge that may be occurring are, in effect, included by using heads measured in 2000 (which should reflect that recharge) to calibrate Culebra transmissivity fields (T fields) and calculate transport through those fields (Beauheim 2002).  Changes (increases) in Culebra transmissivity are incorporated directly in the modeling of flow and transport in the Culebra (see the CCA, Chapter 6.0, Section 6.4.6.2.3).

Potash mining, and the associated processing outside the controlled area, have changed fluid densities within the Culebra, as demonstrated by the areas of higher densities around boreholes WIPP-27 and WIPP-29 (Davies 1989, p. 43).  Transient groundwater flow calculations (Davies 1989, pp. 77–81) show that brine density variations to the west of the WIPP site caused by historical and current potash processing operations will not persist because the rate of groundwater flow in this area is fast enough to flush the high-density groundwaters to the Pecos River.  These calculations also show that accounting for the existing brine density variations in the region east of the WIPP site, where hydraulic conductivities are low, would have little effect on the direction or rate of groundwater flow.  Therefore, changes in fluid densities from historical and current human EPs have been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.

The distribution of existing leases and potash grades suggests that near-future mining will take place to the north, west, and south of the controlled area (see the CCA, Appendix DEL).  A localized increase in fluid density in the Culebra, in the mined region or elsewhere outside the controlled area, would rotate the flow vector towards the downdip direction (towards the east).  A comparison of the relative magnitudes of the pressure gradient and the density gradient (based on an analysis identical to that presented for fluid leakage to the Culebra through boreholes) shows that the density effect is of low consequence to the performance of the disposal system.

Consistent with section 194.32(b), consideration of future mining may be limited to potash mining within the disposal system.  Within the controlled area, the McNutt provides the only potash of appropriate quality.  The extent of possible future potash mining within the controlled area is discussed in the CCA, Chapter 2.0, Section 2.3.1.1.  Criteria concerning the consequence modeling of future mining are provided in section 194.32(b): the effects of future mining may be limited to changes in the hydraulic conductivity of the hydrogeologic units of the disposal system.  Thus, consistent with section 194.32(b), changes in groundwater flow due to mining within the controlled area are accounted for in calculations of the DP of the disposal system (see the CCA, Chapter 6.0, Section 6.4.6.2.3).

Changes in Geochemistry due to Mining (HCN) have been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.  Future Changes in Geochemistry due to Mining have been eliminated from PA calculations on regulatory grounds.

No new information has been identified for this FEP.

Potash mining is the only excavation activity currently taking place in the vicinity of the WIPP that could affect hydrogeological or geochemical conditions in the disposal system.  Potash is mined in the region east of Carlsbad and up to 5 km (1.5 mi) from the boundaries of the controlled area.  Mining of the McNutt in the Salado is expected to continue in the vicinity of the WIPP (see the CCA, Chapter 2.0, Section 2.3.1.1): the DOE assumes that all economically recoverable potash in the vicinity of the WIPP (outside the controlled area) will be extracted in the near future.

Fluid flow associated with excavation activities may result in geochemical disturbances of the disposal system.  Some waters from the Culebra reflect the influence of current potash mining, having elevated potassium to sodium ratios.  However, potash mining has had no significant effect on the geochemical characteristics of the disposal system.  Solution mining, which involves the injection of freshwater to dissolve the ore body, can be used for extracting sylvite.  The impact on the WIPP of neighboring potash mines was examined in greater detail by D’Appolonia (1982).  D’Appolonia noted that attempts to solution mine sylvite in the Delaware Basin failed because of low ore grade, thinness of the ore beds, and problems with heating and pumping injection water.  See discussion in Section SCR-5.1.2.1 (Conventional Underground Potash Mining [H13]). Thus changes in geochemistry due to mining (HCN) have been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.

Consistent with section 194.32(b), consideration of future mining may be limited to potash mining within the disposal system.  Within the controlled area, the McNutt provides the only potash of appropriate quality.  The extent of possible future potash mining within the controlled area is discussed in the CCA, Chapter 2.0, Section 2.3.1.1.  Criteria concerning the consequence modeling of future mining are provided in section 194.32(b): the effects of future mining may be limited to changes in the hydraulic conductivity of the hydrogeologic units of the disposal system.  Thus, consistent with section 194.32(b), changes in groundwater flow as a result of mining within the controlled area are accounted for in calculations of the DP of the disposal system (see the CCA, Chapter 6.0, Section 6.4.6.2.3).  Other potential effects, such as changes in geochemistry due to mining, have been eliminated from PA calculations on regulatory grounds.

HCN and future Solution Mining for Potash has been eliminated from PA calculations on regulatory grounds.  HCN and future solution mining for other resources has been eliminated from PA calculations on the basis of low consequence to the performance of the disposal system.

Plans for the development of a potash solution mine in the region continue, although the solution process has not begun; the project remains in the permitting and planning stage.  The project lies outside the Delaware Basin, but the DOE maintains communication with the leaseholder and the U.S. Bureau of Land Management to monitor project status.

Currently, no solution mining for potash occurs in the CPD.  The prospect of using solution-mining techniques for extracting potash has been identified in the region, but has not been implemented.  A pilot plant for secondary solution mining of sylvite in the Clayton Basin, just north of the Delaware Basin was permitted, and concept planning took place during the mid-1990s and was noted by the EPA in their Response to Comments to the CCA (U.S. Environmental Agency 1998c).  Continued progress has been made towards initiating this project, but as of the submittal of this recertification application, the project has not begun.  The project intends to solution mine sylvite from retired underground mine workings at the old Potash Corporation of America lease.  To date, discharge permits have been filed with the State of New Mexico, but are pending.  Therefore, it is premature to consider this an operational solution mining activity.  More importantly, the proposed site is outside the Delaware Basin.

The potash reserves evaluated by Griswold and Griswold (1999) and New Mexico Bureau of Mines and Mineral Resources (1995) at the WIPP are of economic importance in only two ore zones; the 4th and the 10th contain two minerals of economic importance, langbeinite and sylvite. The ore in the 10th ore zone is primarily sylvite with some langbeinite and the ore in the 4th zone is langbeinite with some sylvite.  Langbeinite falls between gypsum and polyhalite in solubility and dissolves at a rate 1000 times slower than sylvite (Heyn 1997).  Halite, the predominate gangue mineral present, is much more soluble than the langbeinite. Because of the insolubility of langbeinite, sylvite is the only potash ore in the WIPP vicinity that could be mined using a solution mining process. Mining for sylvite by solutioning would cause the langbeinite to be lost because conventional mining could not be done in conjunction with a solution mining process.

Communiqués with IMC Global (Heyn 1997, Prichard 2003) indicate that rock temperature is critical to the success of a solution-mining endeavor. IMC Global’s solution mines in Michigan and Saskatchewan are at depths of around 914 m (3,000 ft) or greater, at which rock temperatures are higher. The ore zones at the WIPP are shallow, at depths of 457 to 549 m (1,500 to 1,800 ft), with fairly cool rock temperatures. Prichard (2003) states that solution mining is energy intensive and the cool temperature of the rock would add to the energy costs. In addition, variable concentrations of confounding minerals (such as kainite and leonite) will cause problems with the brine chemistry.

Typically, solution mining is used for potash

·       When deposits are at depths in excess of 914 m (3,000 ft) and rock temperatures are high, or are geologically too complex to mine profitably using conventional underground mining techniques

·       To recover the potash pillars at the end of a mine’s life

·       When a mine is unintentionally flooded with waters from underlying or overlying rock strata and conventional mining is no longer feasible

Douglas W. Heyn (chief chemist of IMC Kalium) provided written testimony to the EPA related to the Agency’s rulemaking activities on the CCA.  Heyn concluded that “the rational choice for extracting WIPP potash ore reserves would be by conventional room and pillar mechanical means” (Heyn 1997).  It is the opinion of IMC Global that no company will ever attempt solution mining of the ores in or near the WIPP (Heyn 1997, Prichard 2003).

The impact on the WIPP of neighboring potash mines and the possible effects of solution mining for potash or other evaporite minerals were examined in detail by D’Appolonia (1982).  According to D’Appolonia (1982), and in agreement with Heyn (1997) of IMC Global, Inc., solution mining of langbeinite is not technically feasible because the ore is less soluble than the surrounding evaporite minerals.  Solution mining of sylvite was unsuccessfully attempted in the past by the Potash Company of America and Continental Potash. Both ore bodies are currently owned by Mississippi Chemical.  Failure of solution mining was attributed to low ore grade, thinness of the ore beds, and problems with heating and pumping injection water.  Unavailability of water in the area would also impede implementation of this technique.  For these reasons, solution mining is not currently used in the CPD.

Serious technical and economic obstacles exist that render solution mining for potash very unlikely in the vicinity of the WIPP.  Expectedly, no operational example of this technology exists in the CPD; that is, solution mining for potash in not considered a current practice in the area.  For this reason, consideration of solution mining on the disposal system in the future may be excluded on regulatory grounds.  For example, the EPA stated in their Response to Comments, Section 8, Issue GG (EPA 1998c):

…However, the Agency emphasizes that, in accordance with the WIPP compliance criteria, solution mining does not need to be included in the PA.  As previously discussed, potash solution mining is not an ongoing activity in the Delaware Basin.  Section 194.32(b) of the rule limits assessment of mining effects to excavation mining.  Thus the solution mining scenarios proposed are excluded on regulatory grounds after repository closure.  Prior to or soon after disposal, solution mining is an activity that could be considered under Section 194.32(c).  However, DOE found that potash solution mining is not an ongoing activity in the Delaware Basin; and one pilot project examining solution mining in the Basin is not substantive evidence that such mining is expected to occur in the near future.  (Even if mining were assumed to occur in the near future, the proposed scenarios would not be possible because, even though solution mining might occur, there would be no intruding borehole to provide a pathway into the repository:  active institutional controls would preclude such drilling during the first 100 years after disposal.)  Furthermore, Section 194.33(d) states that PA need not analyze the effects of techniques used for resource recovery (e.g. solution mining) after a borehole is drilled in the future.

No new data or information have become available that compromise, reduce, or invalidate the project’s position on whether solution mining for potash should be included in the PA calculations.  T