UGTA Closure Strategy and Contaminant Modeling Overview

1. Underground Test Area (UGTA) Overview Bill Wilborn UGTA Federal Sub-Project Director 2011 Community Environmental Monitoring Program (CEMP) Workshop July 26, 2011

2. Presentation Topics • UGTA Strategy Overview • Corrective Action Unit (CAU) Status/Changes

3. UGTA Closure Strategy • Corrective Action Investigation (Phase I and II) • Corrective Action Investigation Plan (CAIP) • Data collection • Modeling • Contaminant boundary • Peer review

4. UGTA Closure Strategy (continued) • Corrective Action Decision/Corrective Action Plan • Corrective Action Decision Document/ Corrective Action Plan (CADD/CAP) • Use restriction boundary • Regulatory boundary • Model evaluation

5. UGTA Closure Strategy (continued) • Closure • Closure Report (CR) • Address boundary changes from model evaluation • Closure in place with long-term monitoring • Institutional controls

6. Frenchman Flat • FY 2010 completed Peer Review/Model accepted by State of Nevada Division of Environmental Protection (NDEP) • Currently completing CADD/CAP – the first one for UGTA • Building first two roads and pads for model evaluation wells • American Recovery and Reinvestment Act funded • Sites identified as ER-5-5 and ER-11-2

7. Frenchman Flat Well Sites • ER-5-5 • ER-11-2

8. Yucca Flat • Initiating scoping of supplemental analysis for flow and transport modeling (outcome from Preemptive Review) • Models captured reasonable range of outcomes maximizing extent of contamination • Low probability any water with radionuclide concentrations exceeding maximum contaminant level will leave Yucca Flat • Most radionuclide inventory is retained within the vadose zone or saturated volcanics • Extent of lower carbonate aquifer (LCA) exceedence volume (EV) is controlled by non-sorbing radionuclides from a small fraction of the tests

9. Yucca Flat(continued) • Tests with working points in the unsaturated zone contribute little to the LCA EV or to maximum southern extent of contamination in the LCA • Key sensitivities with faults creating fast path from the volcanics to the LCA – major faults control the extent of migration Conclusion: Extend Phase I to focus on major uncertainties and address during CADD/CAP model evaluation

10. Rainier Mesa/Shoshone Mountain • Continuing flow and transport model analysis and evaluation • Concluded pre-emptive review held end of March for opening discussion with NDEP on path forward • Similar strategy considerations for Yucca Flat need to be made for Rainier Mesa/Shoshone Mountain in regard to where focus on uncertainties should be

11. Rainier Mesa/Shoshone Mountain(continued) • Tests Clearwater and Wineskin seem to dominate radionuclide transport to saturated zone; these two tests make up 25% of the Rainier Mesa/Shoshone Mountain inventory • Path forward may be similar to Yucca Flat in that an extended Phase I may need to be implemented then move to CADD/CAP and model evaluation

12. Pahute Mesa • Will complete well development, testing, and sampling for three wells: • ER-20-4 (one completion zone) • ER-20-8 (two completion zones) • ER-EC-12 (two completion zones) • Phase II drilling campaign and geology • ER-20-7 • ER-20-8 • ER-20-8 #2 • ER-EC-11 • ER-EC-12 • ER-20-4 • ER-EC-13 • ER-EC-15

16. What Have We Learned to Date? • Newly acquired data supports the conceptual model • Contamination moves off Pahute Mesa in deeper units to stratigraphically higher units as caldera structure down drops the volcanics to the south • The Benham Aquifer is hypothesized to be the main aquifer of concern at the leading edge of the contaminant plume • Additional well installation and hydraulic testing are designed to increase confidence in our modeling strategy

17. Radiation Facts