Title 40 CFR Part 191
Subparts B and C
Compliance Recertification Application 2014
for the
Waste Isolation Pilot Plant

Appendix SCR-2014
Feature, Event, and Process Screening for PA

United States Department of Energy
Waste Isolation Pilot Plant

Carlsbad Field Office
Carlsbad, New Mexico


Compliance Recertification Application 2014 Appendix SCR-2014
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-4.1.1.2.3

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-4.1.3.2.4.4 Causes 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-4.1.4.2.1 Screening 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-4.1.4.2.4.1 Summary of New Information

SCR-4.1.4.2.4.2 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-4.1.5.2.3 Screening 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-4.2 Subsurface 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 (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-4.4.1.1.2 Summary 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-5.1.1.3.3.2 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-5.2.1.2.3 Screening 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 Future Human EPs - Boreholes That Do Not Intersect the Waste Disposal Region

SCR-5.2.1.4.3.5 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-5.2.1.12.3 Screening 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-5.7.2.2.3 Screening 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-6.2.1.2.3 Screening Argument

SCR-6.2.1.3 FEPs Number: W14 FEPs Title: Nuclear Criticality: Heat

SCR-6.2.1.3.1 Screening Decision: SO-P

SCR-6.2.1.3.2 Summary of New Information

SCR-6.2.1.3.3 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-6.3.5.2.3 Screening 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: Gases 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-6.5.1.6.2 Summary 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 (Shaft) 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 (W74 and W76) SO-P (W115)

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 Summary for CRA-2014

Table SCR- 2. Delaware Basin Brine Well Status

Table SCR- 3. Changes in Inventory Quantities from the CCA to the CRA-20 14

Table SCR- 4. CCA and CRA Exothermic Temperature Rises


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Acronyms and Abbreviations

mm micrometer

AIC active institutional controls

Bq becquerels

°C degrees centigrade

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

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

°F degrees Fahrenheit

FEP feature, event, and process

FLAC Fast Lagrangian Analysis Continua

FSU Florida State University

ft foot/feet

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/inches

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

OB outside boundary

oz ounce

PA performance assessment

PABC Performance Assessment Baseline Calculation

PAVT Performance Assessment Verification Test

PCN planned change notice

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

SDDI Salt Defense Disposal Investigations

SDI Salt Disposal Investigations

SKI Statens Kärnkraftinspektion

SO-C screened-out consequence

SO-P screened-out probability

SO-R screened-out regulatory

T-field transmissitivity field

TRU transuranic

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

yd3 cubic yard

yr year

yrs years

Elements and Chemical Compounds

Al aluminum

Am americium

An actinide

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. EPA 1998a, p. 27405) established in 40 CFR Part 191 Subparts B and C (U.S. EPA 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. DOE 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 (yrs). As such, the DOE prepared the 2004 Compliance Recertification Application (CRA-2004) (U.S. DOE 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. As a result of the CRA-2004 and information provided in response to specific requests, the EPA recertified the WIPP on March 29, 2006 (U.S. EPA 2006). Subsequently, this recertification process was repeated by the DOE with its submittal of the CRA-2009 (U.S. DOE 2009). Again, the EPA carefully reviewed the application, and after requesting additional information and calculations, recertified that the WIPP continued to comply with the long-term disposal requirements of 40 CFR Part 191 and the compliance criteria of 40 CFR Part 194 (U.S. EPA 1996a) in November 2010 (U.S. EPA 2010a). Currently, and in compliance with the requirements for periodic recertification, the DOE has prepared the CRA-2014, which documents changes since the CRA-2009, 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 are 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, the CRA-2009, and this CRA-2014 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 3) (Kirkes 2013a). For the CRA-2014, a reassessment of FEPs concluded that of the 245 FEPs considered for the CRA-2009, 184 have not been changed and 61 have been updated with new information. Of the 61 updated FEPs, one has also had its screening decision changed. Therefore, there are 245 WIPP FEPs for the CRA-2014.

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 section 191.13 (U.S. EPA 1993). These requirements state that the DOE must use PA to demonstrate that radionuclide releases from the disposal system during the 10,000 yrs 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 section 194.32 (U.S. EPA 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 (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 and duplications 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 were 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 were represented by a single FEP, Disruption Due to Gas Effects.

· FEPs that were 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 were represented by the FEP Inhalation.

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

· A few FEPs were 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. As mentioned in Section SCR-1.0, the FEPs baseline is managed by procedure to be systematically reviewed and updated prior to each recertification application. As a result of this process, the CRA-2004 included 235 WIPP FEPs, and both the CRA-2009 and CRA-2014 include 245 WIPP FEPs. These evaluations are documented in Wagner et al. (Wagner et al. 2003), Kirkes (Kirkes 2008), and Kirkes (Kirkes 2013b), respectively.

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 section 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, section 194.34 (a) (U.S. EPA 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 section 191.12 (U.S. EPA 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 section 191.15 (U.S. EPA 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. Identifiers (IDs) of Natural FEPs begin with "N," IDs of Human-Induced EPs begin with "H," 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 Section SCR-2.4.2.

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 section 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 section 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 section 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 section 194.33 (U.S. EPA 1996a). The EPA also provides a criterion in section 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. These 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 section 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 closure system (PCS), 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 2013b) results in a new FEPs baseline for CRA-2014. As discussed in Section SCR-1.0, 184 of the 245 WIPP FEPs have not changed since the CRA-2009. However, 61 FEPs required updates to their FEP descriptions and/or screening arguments, one of which has also had its screening decision changed. The single screening decision change does not result in a new FEP incorporated into PA calculations; the particular FEP will now be screened out of PA. Thus, the CRA-2014 considers 245 WIPP FEPs.

Table SCR-1 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-1 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 its Technical Support Document for section 194.32 (U.S. EPA 1998b).


Table SCR- 1. FEPs Summary for CRA-2014

EPA FEP I.D.a ,b ,c, d

FEP Name

Screening Argument Update?

Screening Decision Changed?

Screening Classification

N1

Stratigraphy

No change

No

UP

N2

Brine Reservoirs

Updated by new PA parameter GLOBAL:PBRINE

No

DP

N3

Changes in Regional Stress

No change

No

SO-C

N4

Regional Tectonics

No change

No

SO-C

N5

Regional Uplift and Subsidence

No change

No

SO-C

N6

Salt Deformation

No change

No

SO-P

N7

Diapirism

No change

No

SO-P

N8

Formation of Fractures

No change

No

SO-P
UP (Repository)

N9

Changes in Fracture Properties

No change

No

SO-C
UP (Near Repository)

N10

Formation of New Faults

No change

No

SO-P

N11

Fault Movement

No change

No

SO-P

N12

Seismic Activity

Updated with new seismic data

No

UP

N13

Volcanic Activity

No change

No

SO-P

N14

Magmatic Activity

No change

No

SO-C

N15

Metamorphic Activity

No change

No

SO-P

N16

Shallow Dissolution

No change

No

UP

N18

Deep Dissolution

No change

No

SO-P

N20

Breccia Pipes

No change

No

SO-P

N21

Collapse Breccias

No change

No

SO-P

N22

Fracture Infills

No change

No

SO-C - Beneficial

N23

Saturated Groundwater Flow

No change

No

UP

N24

Unsaturated Groundwater Flow

No change

No

UP

N25

Fracture Flow

No change

No

UP

N27

Effects of Preferential Pathways

No change

No

UP

N26

Density Effects on Groundwater Flow

No change

No

SO-C

N28

Thermal Effects on Groundwater Flow

No change

No

SO-C

N29

Saline Intrusion (Hydrogeological Effects)

No change

No

SO-P

N30

Freshwater Intrusion (Hydrogeological Effects)

No change

No

SO-P

N31

Hydrological Response to Earthquakes

No change

No

SO-C

N32

Natural Gas Intrusion

No change

No

SO-P

N33

Groundwater Geochemistry

No change

No

UP

N34

Saline Intrusion (Geochemical Effects)

No change

No

SO-C

N38

Effects of Dissolution

No change

No

SO-C

N35

Freshwater Intrusion (Geochemical Effects)

No change

No

SO-C

N36

Changes in Groundwater Eh

No change

No

SO-C

N37

Changes in Groundwater pH

No change

No

SO-C

N39

Physiography

No change

No

UP

N40

Impact of a Large Meteorite

No change

No

SO-P

N41

Mechanical Weathering

No change

No

SO-C

N42

Chemical Weathering

No change

No

SO-C

N43

Aeolian Erosion

No change

No

SO-C

N44

Fluvial Erosion

No change

No

SO-C

N45

Mass Wasting (Erosion)

No change

No

SO-C

N46

Aeolian Deposition

No change

No

SO-C

N47

Fluvial Deposition

No change

No

SO-C

N48

Lacustrine Deposition

No change

No

SO-C

N49

Mass Wasting (Deposition)

No change

No

SO-C

N50

Soil Development

No change

No

SO-C

N51

Stream and River Flow

No change

No

SO-C

N52

Surface Water Bodies

No change

No

SO-C

N53

Groundwater Discharge

No change

No

UP

N54

Groundwater Recharge

No change

No

UP

N55

Infiltration

No change

No

UP

N56

Changes in Groundwater Recharge and Discharge

No change

No

UP

N57

Lake Formation

No change

No

SO-C

N58

River Flooding

No change

No

SO-C

N59

Precipitation (e.g., Rainfall)

No change

No

UP

N60

Temperature

No change

No

UP

N61

Climate Change

No change

No

UP

N62

Glaciation

No change

No

SO-P

N63

Permafrost

No change

No

SO-P

N64

Seas and Oceans

No change

No

SO-C

N65

Estuaries

No change

No

SO-C

N66

Coastal Erosion

No change

No

SO-C

N67

Marine Sediment Transport and Deposition

No change

No

SO-C

N68

Sea Level Changes

No change

No

SO-C

N69

Plants

No change

No

SO-C

N70

Animals

No change

No

SO-C

N71

Microbes

No change

No

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

N72

Natural Ecological Development

No change

No

SO-C

H1

Oil and Gas Exploration

Updated with new drilling rate

No

SO-C (HCN)
DP (Future)

H2

Potash Exploration

No change

No

SO-C (HCN)
DP (Future)

H4

Oil and Gas Exploitation

Updated with new drilling rate

No

SO-C (HCN)
DP (Future)

H8

Other Resources

No change

No

SO-C (HCN)
DP (Future)

H9

Enhanced Oil and Gas Recovery

No change

No

SO-C (HCN)
DP (Future)

H3

Water Resources Exploration

Updated with most recent monitoring information

No

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

H5

Groundwater Exploitation

Updated with most recent monitoring information

No

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

H6

Archaeological Investigations

No change

No

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

H7

Geothermal

No change

No

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

H10

Liquid Waste Disposal

No change

No

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

H11

Hydrocarbon Storage

No change

No

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

H12

Deliberate Drilling Intrusion

No change

No

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

H13

Conventional Underground Potash Mining

No change

No

UP (HCN)
DP (Future)

H14

Other Resources (Mining For)

No change

No

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

H15

Tunneling

No change

No

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

H16

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

No change

No

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

H17

Archaeological Excavations

No change

No

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

H18

Deliberate Mining Intrusion

No change

No

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

H19

Explosions for Resource Recovery

No change

No

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

H20

Underground Nuclear Device Testing

No change

No

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

H21

Drilling Fluid Flow

No change

No

SO-C (HCN)
DP (Future)

H22

Drilling Fluid Loss

No change

No

SO-C (HCN)
DP (Future)

H23

Blowouts

Updated with new parameter GLOBAL:PBRINE

No

SO-C (HCN)
DP (Future)

H24

Drilling-Induced Geochemical Changes

No change

No

UP (HCN)
DP (Future)

H25

Oil and Gas Extraction

No change

No

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

H26

Groundwater Extraction

No change

No

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

H27

Liquid Waste Disposal-Outside Boundary (OB)

No change

No

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

H28

Enhanced Oil and Gas Production-OB

No change

No

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

H29

Hydrocarbon Storage-OB

No change

No

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

H60

Liquid Waste Disposal-Inside Boundary (IB)

No change

No

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

H61

Enhanced Oil and Gas Production-IB

No change

No

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

H62

Hydrocarbon Storage-IB

No change

No

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

H30

Fluid-Injection Induced Geochemical Changes

No change

No

UP (HCN)
SO-R (Future)

H31

Natural Borehole Fluid Flow

Updated to reflect new plugging probabilities

No

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

H32

Waste-Induced Borehole Flow

Updated to reflect new plugging probabilities

No

SO-R (HCN)
DP (Future)

H34

Borehole-Induced Solution and Subsidence

No change

No

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

H35

Borehole-Induced Mineralization

No change

No

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

H36

Borehole-Induced Geochemical Changes

No change

No

UP (HCN)
DP (Future)

SO-C (for units other than the Culebra)

H37

Changes in Groundwater Flow Due to Mining

No change

No

UP (HCN)
DP (Future)

H38

Changes in Geochemistry Due to Mining

No change

No

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

H39

Changes in Groundwater Flow Due to Explosions

No change

No

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

H40

Land Use Changes

No change

No

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

H41

Surface Disruptions

No change

No

UP (HCN)
SO-C (Future)

H42

Damming of Streams or Rivers

No change

No

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

H43

Reservoirs

No change

No

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

H44

Irrigation

No change

No

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

H45

Lake Usage

No change

No

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

H46

Altered Soil or Surface Water Chemistry by Human Activities

No change

No

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

H47

Greenhouse Gas Effects

No change

No

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

H48

Acid Rain

No change

No

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

H49

Damage to the Ozone Layer

No change

No

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

H50

Coastal Water Use

No change

No

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

H51

Sea Water Use

No change

No

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

H52

Estuarine Water Use

No change

No

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

H53

Arable Farming

No change

No

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

H54

Ranching

No change

No

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

H55

Fish Farming

No change

No

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

H56

Demographic Change and Urban Development

No change

No

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

H57

Loss of Records

No change

No

NA (HCN)
DP (Future)

H58

Solution Mining for Potash

Updated with information regarding solution mining activities in the region

No

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

H59

Solution Mining for Other Resources

Updated with new information regarding brine wells in the region

No

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

W1

Disposal Geometry

Updated with new information regarding additional mined area used for experiments

No

UP

W2

Waste Inventory

Updated to reflect the inventory data sources used for the CRA-2014 PA

No

UP

W3

Heterogeneity of Waste Forms

Updated to reflect the inventory data sources used for the CRA-2014 PA

No

DP

W4

Container Form

Updated to reflect the inventory data sources used for the CRA-2014 PA

No

SO-C - Beneficial

W5

Container Material Inventory

Updated to reflect the inventory data sources used for the CRA-2014 PA

No

UP

W6

Shaft Seal Geometry

No change

No

UP

W7

Shaft Seal Physical Properties

No change

No

UP

W109

Panel Closure Geometry

Updated with new information on panel closure design

No

UP

W110

Panel Closure Physical Properties

Updated with new information on panel closure design

No

UP

W8

Shaft Seal Chemical Composition

No change

No

SO-C Beneficial

W111

Panel Closure Chemical Composition

Updated with new information on panel closure design

No

SO-C Beneficial

W9

Backfill Physical Properties

No change

No

SO-C

W10

Backfill Chemical Composition

Updated to reflect implementation of water balance in PA

No

UP

W11

Post-Closure Monitoring

No change

No

SO-C

W12

Radionuclide Decay and In-Growth

No change

No

UP

W13

Heat from Radioactive Decay

Updated to reflect the inventory used for the CRA-2014 PA

No

SO-C

W14

Nuclear Criticality: Heat

Updated to reflect the inventory used for the CRA-2014 PA

No

SO-P

W15

Radiological Effects on Waste

Updated to reflect the inventory used for the CRA-2014 PA

No

SO-C

W16

Radiological Effects on Containers

Updated to reflect the inventory used for the CRA-2014 PA

No

SO-C

W17

Radiological Effects on Shaft Seals

Updated to reflect the inventory used for the CRA-2014 PA

No

SO-C

W112

Radionuclide Effects on Panel Closures

Updated to reflect the inventory used for the CRA-2014 PA

No

SO-C

W18

Disturbed Rock Zone (DRZ)

Updated to include new panel closure implementation

No

UP

W19

Excavation-Induced Changes in Stress

Updated to include new panel closure implementation

No

UP

W20

Salt Creep

Updated to include new panel closure implementation

No

UP

W21

Changes in the Stress Field

Updated to include new panel closure implementation

No

UP

W22

Roof Falls

No change

No

UP

W23

Subsidence

No change

No

SO-C

W24

Large Scale Rock Fracturing

No change

No

SO-P

W25

Disruption Due to Gas Effects

No change

No

UP

W26

Pressurization

Updated to reference new corrosion experiments and associated parameters

No

UP

W27

Gas Explosions

No change

No

UP

W28

Nuclear Explosions

Updated to reflect the inventory used for the CRA-2014 PA

No

SO-P

W29

Thermal Effects on Material Properties

Updated to reflect the inventory used for the CRA-2014 and planned thermal experiments

No

SO-C

W30

Thermally-Induced Stress Changes

Updated to reflect the inventory used for the CRA-2014 and planned thermal experiments

No

SO-C

W31

Differing Thermal Expansion of Repository Components

Updated to reflect the inventory used for the CRA-2014 and planned thermal experiments

No

SO-C

W72

Exothermic Reactions

Updated to reflect the inventory used for the CRA-2014 and planned thermal experiments

No

SO-C

W73

Concrete Hydration

Updated to reflect the inventory used for the CRA-2014 and planned thermal experiments

No

SO-C

W32

Consolidation of Waste

No change

No

UP

W36

Consolidation of Shaft Seals

No change

No

UP

W37

Mechanical Degradation of Shaft Seals

No change

No

UP

W39

Underground Boreholes

No change

No

UP

W113

Consolidation of Panel Closures

Updated screening argument with new information regarding panel closure composition

No

UP

W114

Mechanical Degradation of Panel Closures

Updated screening argument with new information regarding panel closure composition

No

UP

W33

Movement of Containers

Updated to reference new inventory data

No

SO-C

W34

Container Integrity

No change

No

SO-C Beneficial

W35

Mechanical Effects of Backfill

No change

No

SO-C

W40

Brine Inflow

Updated to reflect water balance implementation in PA

No

UP

W41

Wicking

Updated to reflect water balance implementation in PA

No

UP

W42

Fluid Flow Due to Gas Production

Updated to reflect water balance implementation in PA and new steel corrosion rates

No

UP

W43

Convection

Updated to reflect planned thermal experiments

No

SO-C

W44

Degradation of Organic Material

Updated to reference new inventory data

No

UP

W45

Effects of Temperature on Microbial Gas Generation

Updated to reference new inventory data

No

UP

W48

Effects of Biofilms on Microbial Gas Generation

Updated to reference new inventory data

No

UP

W46

Effects of Pressure on Microbial Gas Generation

No change

No

SO-C

W47

Effects of Radiation on Microbial Gas Generation

Updated with new radionuclide inventory and information related to the EPA request for additional information on CRA-2009

No

SO-C

W49

Gases from Metal Corrosion

Updated to reference new corrosion experiments and inventory

No

UP

W51

Chemical Effects of Corrosion

Updated to reference new corrosion experiments and inventory

No

UP

W50

Galvanic Coupling (Within the Repository)

No change

No

SO-C

W52

Radiolysis of Brine

No change

No

SO-C

W53

Radiolysis of Cellulose

Screening argument updated with new radionuclide inventory

No

SO-C

W54

Helium Gas Production

Screening argument updated with new radionuclide inventory

No

SO-C

W55

Radioactive Gases

Updated to reference new inventory data

No

SO-C

W56

Speciation

Reference made to new solubility calculations based on new inventory components

No

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

W57

Kinetics of Speciation

No change

No

SO-C

W58

Dissolution of Waste

No change

No

UP

W59

Precipitation of Secondary Minerals

No change

No

SO-C Beneficial

W60

Kinetics of Precipitation and Dissolution

No change

No

SO-C

W61

Actinide Sorption

No change

No

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 change

No

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 change

No

UP

W64

Effects of Metal Corrosion

No change

No

UP

W66

Reduction-Oxidation Kinetics

No change

No

UP

W65

Reduction-Oxidation Fronts

No change

No

SO-P

W67

Localized Reducing Zones

No change

No

SO-C

W68

Organic Complexation

Updated to reflect implementation of variable brine volume in PA

No

UP

W69

Organic Ligands

Updated to reflect implementation of variable brine volume, new inventory data

No

UP

W71

Kinetics of Organic Complexation

No change

No

SO-C

W70

Humic and Fulvic Acids

No change

No

UP

W74

Chemical Degradation of Shaft Seals

No change

No

UP

W76

Microbial Growth on Concrete

No change

No

UP

W115

Chemical Degradation of Panel Closures

Updated screening argument with new panel closure materials

Yes

SO-P

W75

Chemical Degradation of Backfill

No change

No

SO-C

W77

Solute Transport

No change

No

UP

W78

Colloid Transport

No change

No

UP

W79

Colloid Formation and Stability

No change

No

UP

W80

Colloid Filtration

No change

No

UP

W81

Colloid Sorption

No change

No

UP

W82

Suspensions of Particles

No change

No

DP

W83

Rinse

No change

No

SO-C

W84

Cuttings

No change

No

DP

W85

Cavings

Updated with new waste shear strength data

No

DP

W86

Spallings

Updated with new water balance implementation

No

DP

W87

Microbial Transport

No change

No

UP

W88

Biofilms

No change

No

SO-C Beneficial

W89

Transport of Radioactive Gases

Updated to reference CRA-2014 inventory data

No

SO-C

W90

Advection

No change

No

UP

W91

Diffusion

No change

No

UP

W92

Matrix Diffusion

No change

No

UP

W93

Soret Effect

Updated based on new inventory data

No

SO-C

W94

Electrochemical Effects

No change

No

SO-C

W95

Galvanic Coupling (Outside the Repository)

No change

No

SO-P

W96

Electrophoresis

No change

No

SO-C

W97

Chemical Gradients

No change

No

SO-C

W98

Osmotic Processes

No change

No

SO-C

W99

Alpha Recoil

No change

No

SO-C

W100

Enhanced Diffusion

No change

No

SO-C

W101

Plant Uptake

No change

No

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

W102

Animal Uptake

No change

No

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

W103

Accumulation in Soils

No change

No

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

W104

Ingestion

No change

No

SO-R
SO-C (for section 191.15)

W105

Inhalation

No change

No

SO-R
SO-C (for section 191.15)

W106

Irradiation

No change

No

SO-R
SO-C (for section 191.15)

W107

Dermal Sorption

No change

No

SO-R
SO-C (for section 191.15)

W108

Injection

No change

No

SO-R
SO-C (for section 191.15)

a N = Natural FEP

b H = Human-induced event and process (EP)

c W = Waste- and Repository-induced FEP

d FEPs in this column that are not separated by rows represent FEPs that are similar in nature and are discussed and screened as a common group.


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 and two have 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.

Since the CRA-2009, new information has been gathered and analyzed that supports changing the probability that pressurized brine will be intercepted in WIPP intrusion scenarios. Kirchner et al. (Kirchner et al. 2012) describes the methodology and rationale for arriving at the updated parameter distribution for the PA parameter GLOBAL:PBRINE. This updated parameter does not change the screening argument or decision from the CRA-2009; brine reservoirs continue to be included in disturbed performance scenarios (DP).

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-2014, Section PA-4.2.1 ). The presence of brine reservoirs is accounted for in the treatment of inadvertent drilling (Appendix PA-2014, 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 that affects the screening of this FEP has been identified since the CRA-2009.

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 (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 (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 (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. (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 yrs continue, the extent of regional uplift and subsidence over the next 10,000 yrs would only be approximately 1 meter (m) (about several feet [ft]]). 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. (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 ft per mile [ft/mi]), has been superimposed on the sedimentary sequence. King (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 (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 yrs 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 (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 yrs 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 (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 (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 yrs 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. (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 (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 (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 (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 (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 that affects the screening of this FEP has been identified since the CRA-2009.

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; Borns 1987). Diapirism occurs when the deformation is penetrative, i.e., halite beds disrupt overlying anhydrites. As Anderson and Powers (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. (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 (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 that affects the screening of this FEP has been identified since the CRA-2009.

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 (Powers and Holt 1999 and Powers and Holt 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 that affects the screening of this FEP has been identified since the CRA-2009.

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 Powers and Holt 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 have been incorporated into the transmissivity values for the CRA-2009 Performance Assessment Baseline Calculation (PABC).

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 new information that affects the screening of this FEP has been identified since the CRA-2009.

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. (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 (Holt and Powers 1988; also included in the CCA, Appendix FAC) note that there is displacement of the Rustler, and Schiel (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. (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 resource production (see Section SCR-4.1.3.2.4.2 for more information on seismic events in the area). 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 Powers and Holt 2000), the possibility of past or future halite dissolution along the margins cannot be ruled out (Holt and Powers 1988; Beauheim and Holt 1990). 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 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.

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

Since the CCA, a much more rigorous seismic monitoring system has been developed by the New Mexico Institute of Mining and Technology (NMIMT). This enhanced monitoring network has greatly increased the sensitivity and detection capability of previous systems. Beginning in 2007, the Delaware Basin Drilling Surveillance Program (DBDSP) also improved its seismic database, allowing the identification and incorporation of data previously unavailable. Using this expanded database, the DBDSP identified 703 seismic events recorded within approximately 300 km (187 mi) from the WIPP site, most of which (85%) occurred in close proximity to the Dagger Draw gas field, during the 2002 - 2007 timeframe. During the current CRA-2014 monitoring period (October 2007 through December 2012) there were 543 seismic events recorded within approximately 300 km (187 mi) of the WIPP site. One notable seismic event occurred on March 18, 2012, with a magnitude of 2.4. This seismic event was associated with a potash mine roof fall. This event occurred 14 km (9 mi) southwest of the WIPP site (Callicoat 2013). No damage was identified at the WIPP site. With the continued collection of additional data, it is increasingly clear that the overwhelming majority of these seismic events are anthropogenic in nature.

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 (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 (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 (g) and that only minor damage occurred at accelerations up to 0.4 g. Lenhardt (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 yrs (annual probability of occurrence of 10 -4) for events producing ground accelerations of 0.1 g. Ground accelerations of 0.2 g 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-2014, 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 that affects the screening of this FEP has been identified since the CRA-2009.

The Paleozoic and younger stratigraphic sequences within the Delaware Basin are devoid of locally derived volcanic rocks. Volcanic ashes (dated at 13 million yrs and 0.6 million yrs) 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 yrs.

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

No new information that affects the screening of this FEP has been identified since the CRA-2009.

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 yrs. 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 A ctivity has been eliminated from PA calculations on the basis of low probability of occurrence over the next 10,000 yrs.

No new information that affects the screening of this FEP has been identified since the CRA-2009.

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 yrs.

Shallow Dissolution is accounted for in PA calculations.

No new information that affects the screening of this FEP has been identified since the CRA-2009.

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, Bachman 1985, and Bachman 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 the 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, Holt and Powers 1986, and Holt and Powers 1990), and the suite of features in these beds led these investigators (Holt and Powers 1988; Powers and Holt 1990 and Powers and Holt 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, Powers and Holt 1999 and Powers and Holt 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 has been 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 the 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 (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 in the derivation of transmissivity fields for Culebra flow and transport.

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

No new information that affects the screening of this FEP has been identified since the CRA-2009.

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. (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 (Anderson 1978, p. 52) and Snyder et al. (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 (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. (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 (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 (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 (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 yrs.

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

No new information that affects the screening of this FEP has been identified since the CRA-2009.

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 (Chapman 1986, p. 31) and Lambert and Harvey (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 yrs-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 that affects the screening of these FEPs has been identified since the CRA-2009.

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 that affects the screening of this FEP has been identified since the CRA-2009.

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 that affects the screening of this FEP has been identified since the CRA-2009.

The geothermal gradient in the region of the WIPP has been measured at about 30 degrees centigrade (°C) (54 degrees Fahrenheit [°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 I ntrusion have been eliminated from PA calculations on the basis of low probability of occurrence over 10,000 yrs.

No new information that affects the screening of this FEP has been identified since the CRA-2009.

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 yrs. 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 I ntrusion have been eliminated from PA calculations on the basis of low probability of occurrence over 10,000 yrs.

No new information that affects the screening of this FEP has been identified since the CRA-2009.

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 yrs.

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

No new information that affects the screening of this FEP has been identified since the CRA-2009.

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. (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 yrs (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 yrs.

No new information that affects the screening of this FEP has been identified since the CRA-2009.

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 yrs.

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

No new information that affects the screening of this FEP has been identified since the CRA-2009.

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 I ntrusion 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 that affects the screening of this FEP has been identified since the CRA-2009.

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 yrs, 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 (Brush 1996) and Brush and Storz (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 used in the CRA-2014 are the same as used in the CRA-2009 PABC.

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-2014 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 that affects the screening of this FEP has been identified since the CRA-2009.

Natural changes in the groundwater chemistry of the Culebra and other units that resulted from saline intrusion or freshwater intrusion could potentially affect chemical retardation and the stability of colloids. Changes in groundwater Eh andgroundwater 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. See Appendix SOTERM-2014, Section 2.3.1 for a discussion of WIPP brine chemistry.

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 (Lambert 1986), Lambert and Carter (Lambert and Carter 1987), and Lambert and Harvey (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 yrs. 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 and Chapman 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).

Past hydrogeological investigations into the cause and effect from observed water-level rises in the Culebra led to a revised groundwater conceptual model (Appendix TFIELD-2014, Section 3.0 ). Continuing hydrogeological studies have seen responses to precipitation events in Culebra wells. This is not to say, however, that present-day rainfall actually enters the Culebra wherever a pressure response to rainfall is observed. Rather, the rainfall reaches a water table in a higher stratigraphic unit that is in sufficient hydraulic communication with the Culebra to transmit a pressure response rapidly. It takes a much longer time for water or dissolved constituents to move through the subsurface than it takes a pressure wave to propagate through a saturated porous medium (Appendix HYDRO-2014, Section 7.1 ).

However, the justification of this screening decision does not depend on this issue. If recharge occurs mainly during periods of high precipitation (pluvials) associated with periods of continental glaciation, the consequences of such recharge are likely 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 yrs 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); and (3) 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 et al. 1991; the CCA, Appendix CLI) established conservative upper limits for precipitation and recharge of the Culebra at the WIPP site. The review by Swift et al. (Swift et al. 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 yrs before the last glacial maximum. Swift et al. (Swift et al. 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 d 18O 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 yrs after the last glaciations had begun. High-resolution, deep-sea d 18O data (and other data) reviewed by Servant (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 yrs 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 that affects the screening of this FEP has been identified since the CRA-2009.

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 yrs.

No new information that affects the screening of this FEP has been identified since the CRA-2009.

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 (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 yrs (equivalent to about 2 ´ 10 -13 impacts per square kilometer (km2) per yr). 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 (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 (Grieve 1987) would correspond to an overall rate of about 1 per 1,000 yrs on the basis of a random distribution.

Assuming the higher estimated impact rate of 17 ´ 10 -13 impacts per square kilometer per yr 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 yr 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 yrs provided in section 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 (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

F 1 = 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 yr), 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 (F 1) of 17 ´ 10 -13 impacts/km2/yr, then Equation (SCR.6) gives a frequency of approximately 5.6 ´ 10 -11 impacts per yr 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 yrs.

Similar calculations have been performed that indicate rates of impact of between 10 -12 and 10 -13 per yr 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 yrs.

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 yrs.

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 that affects the screening of these FEPs has been identified since the CRA-2009.

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 that affects the screening of these FEPs since the CRA-2009.

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 yr) 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 yr 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 yrs.

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 yrs.

Erosion from wind, water, and mass wasting will continue in the WIPP region throughout the next 10,000 yrs 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 that affects the screening of this FEP has been identified since the CRA-2009.

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. (Lappin et al. 1989, pp. 2-4) at 410,000 to 510,000 yrs old, is present in collapse blocks, indicating some growth of Nash Draw in the late Pleistocene. Localized gypsite spring deposits about 25,000 yrs old occur along the eastern flank of Nash Draw, but the springs are not currently active. The Berino soil, interpreted as 333,000 yrs 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 yrs.

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 that affects the screening of these FEPs has been identified since the CRA-2009.

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 yrs 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 that affects the screening of this FEP has been identified since the CRA-2009.

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; Bachman 1974, Bachman 1981, and Bachman 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 that affects the screening of this FEP has been identified since the CRA-2009.

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, Bachman 1981, and Bachman 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 that affects the screening of these FEPs has been identified since the CRA-2009.

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 that affects the screening of this FEP has been identified since the CRA-2009.

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 yrs (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 yrs after any decrease in recharge. Under the anticipated changes in climate over the next 10,000 yrs, 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 are 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, and Appendix PA-2014, Section PA-4.8.3 ).

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 that affects the screening of this FEP has been identified since the CRA-2009.

Intermittent flooding of stream channels and the formation of shallow lakes will occur in the WIPP region over the next 10,000 yrs. 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 formationhave 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 that affects the screening of this FEP has been identified since the CRA-2009.

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-2014, Section PA-4.8 ).

Climate Change is accounted for in PA calculations.

No new information that affects the screening of this FEP has been identified since the CRA-2009.

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 yrs 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-2014, 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 yrs.

No new information that affects the screening of these FEPs has been identified since the CRA-2009.

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 yrs 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 yrs. 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 yrs.

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 that affects the screening of these FEPs has been identified since the CRA-2009.

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 that affects the screening of these FEPs has been identified since the CRA-2009.

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 that affects the screening of this FEP has been identified since the CRA-2009.

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 (Chappell and Shackleton 1986, p. 138). This can have marked effects on coastal aquifers. During the next 10,000 yrs, 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 (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 that affects the screening of this FEP has been identified since the CRA-2009.

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 that affects the screening of this FEP has been identified since the CRA-2009.

Microbes are presumed to be present within the thin soil horizons and in groundwater (Gillow et al. 2000; Swanson and Simmons 2013; Appendix SOTERM-2014, Section 2.4.1 ). The adsorption of actinides, or their analogs, onto microbial surfaces is dependent upon many factors, including biomass concentration, organism type, actinide oxidation state, the presence of complexing agents, matrix ionic strength and pH. These factors, for the key An(III) and An(IV) oxidation states, were accounted for under WIPP-relevant conditions (Reed et al. 2013; Appendix SOTERM-2014, Section 3.9 ). These biocolloids are relatively large in size (>0.3 µ) and exhibit relatively low sorption when compared to the inorganic and organic complexants also present. The density of microbial cells as colloidal particles will be limited by their low relative sorption and will be rapidly reduced by filtration in the Culebra because of their relative large size, leading to the conclusion that microbial colloids will have an insignificant impact on radionuclide transport in the Culebra. A similar conclusion is also observed in other deep geologic disposal concepts (e.g., for the Swedish granite concept (Pederson 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 that affects the screening of this FEP has been identified since the CRA-2009.

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-1 provides summary information regarding changes to human-induced EPs since the CCA. Of the 61 human-induced EPs included in the CRA-2014, 52 remain unchanged, and 9 were updated with new information.

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.

The CRA-2014 will use an updated drilling rate as required by section 194.33. This new rate does not change the screening argument or decision for FEPs H1, Oil and Gas Exploration, H4, Oil and Gas Exploitation, H8, Other Resources, and H9, Enhanced Oil and Gas Recovery. This updated deep drilling rate is implemented through the PA parameter GLOBAL:LAMBDAD. For the CRA-2014, the value for this parameter is 6.73 x 10-3 boreholes per km2 per yr. This is an increase to the value of 5.98 x 10-3 boreholes per km2 per yr used in the CRA-2009 PABC. Additionally, further exploitation of the existing oil leases in Section 31 (beneath the southeast corner of the WIPP site) has occurred via horizontal drilling.

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. (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 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, with the exception of horizontal wells beneath Section 31 (the southwest corner of the WIPP site). Oil leases that pre-existed the withdrawal of land by the Federal government for the WIPP in Section 31 were not condemned, as it was determined that production of these resources could be conducted without adverse effects to the WIPP. As such, the DOE only controls from the surface to 6,000 ft (1,829 m) below ground surface. Operators have continued to produce these leases and four new horizontal wells have been drilled beneath this section since the last recertification application. This continued development and production is consistent with the expectations of the DOE and the EPA (U.S. EPA 1998c). These wells originate outside the WIPP boundary and transition to horizontal orientation at depths below 6,000 ft (1,829 m). The vertical portion of these drill holes lie outside the WIPP boundary. Therefore, it is not expected that vertical wells will be initiated within the WIPP site during the HCN time frame. 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, 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. 2013). 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 section 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. An updated shallow drilling rate of 2.88 x 10-3 boreholes per km2 per yr was calculated in the Delaware Basin Monitoring Annual Report (U.S. DOE 2012). 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 DBDSP continues to collect drilling data related to water resources, as well as other shallow drilling activities. As shown in the DBDSP 2012 Annual Report (U.S. DOE 2012), 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 explorationand groundwater exploitation 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 yrs. 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 section 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 that affects the screening of these FEPs has been identified since the CRA-2009.

No drilling associated with archeology or geothermal energy production has taken place in the Delaware Basin. Consistent with the future states assumptions in section 194.25(a) (U.S. EPA 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 yrs 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 that affects the screening of this FEP has been identified since the CRA-2009.

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.

No new information that affects the screening of this FEP has been identified since the CRA-2009.

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 that affects the screening of this FEP has been identified since the CRA-2009.

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).

Because tunneling and construction of underground facilities (other than the 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 that affects the screening of this FEP has been identified since the CRA-2009.

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 that affects the screening of this FEP has been identified since the CRA-2009.

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 that affects the screening of this FEP has been identified since the CRA-2009.

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 yrs, 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 recovery 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. 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 that affects the screening of this FEP has been identified since the CRA-2009.

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 ft [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. Due to a moratorium on underground nuclear testing, 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.

No new information that affects the screening of this FEP has been identified since the CRA-2009.

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 (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 SCR5.2.1.10, 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 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.

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 L oss into waste panels is accounted for in PA calculations.

No new information that affects the screening of this FEP has been identified since the CRA-2009.

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.

Blowouts are implemented in PA through the parameter GLOBAL:PBRINE, which represents the probability of an inadvertent intrusion borehole encountering pressurized brine beneath the repository. This parameter has been updated based on new data and analysis as reported in Kirchner et al. (Kirchner et al. 2012). This parameter update does not change the screening argument or decision; H23 Blowouts continue to be classified as DP for the future timeframe.

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 2.2.1.2). 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 (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 (Wallace 1996a) analyzed the potential effects of such interconnections in the future within the controlled area (but that do not intersect waste), and concluded 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 that affects the screening of this FEP has been identified since the CRA-2009.

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 (Appendix PA-2004, Attachment MASS, Section MASS-15.2 ). The cumulative distribution functions (CDFs) of Kds used in PA were modified in the CRA-2009 PABC as a result of EPA comments (Clayton 2009). These values are also used in the CRA-2014. 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 yrs (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.

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 section 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 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 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 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 changes that 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.

No new information that affects the screening of this FEP has been identified since the CRA-2009.

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. Additionally, a water well at the Sandia National Laboratories wellpad SNL-14 also provides 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. For undisturbed conditions, there are no radionuclide releases to units above the Salado, and therefore no releases to the accessible environment or producing water wells in the area (Appendix IGP-2014 and Section 53).

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 (Wallace 1996b), using an analytical solution for Darcian fluid flow in a continuous porous medium. Wallace (Wallace 1996b) showed that such a well pumping at about 1.9 liters (L) (0.5 gallon [gal]) per minute for 10,000 yrs 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 yrs. 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.

No new information that affects the screening of this FEP has been identified since the CRA-2009.

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 areenhanced 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 2013). 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; Appendix DATA-2004, 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 yrs 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.

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 (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 (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-yr 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 yrs, 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 (Stoelzel and Swift 1997) expanded on Stoelzel and O'Brien's (Stoelzel and O'Brien 1996) work by considering injection for a longer period of time (up to 150 yrs) 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 (Stoelzel and O'Brien 1996). Rather than repeat the conservative and bounding approach used by Stoelzel and O'Brien (Stoelzel and O'Brien 1996), Stoelzel and Swift (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 (Stoelzel and O'Brien 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 yrs of leakage through a fully degraded cement sheath or 10 yrs 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 (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 (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 (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)

Ñ p = 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)

Ñ Hf = gradient of freshwater head

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

ρf = density of freshwater (kg m -3)

Ñ E = gradient of elevation

Davies (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 (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 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.

Non-locally 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(