Moffett EATS Evaluation Presentation to RAB July 12, 2007

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Moffett EATS Evaluation Presentation to RAB July 12, 2007

  1. 1. Site 26 Evaluation RAB Presentation Former Naval Air Station Moffett Field July 12, 2007 Presented by: Liz Barr Navy Remedial Project Manager
  2. 2. Presentation Outline • Background • Evaluation Objectives – Phase I – Phase II • Results • Summary, Conclusions, and Recommendations • Schedule
  3. 3. BACKGROUND
  4. 4. Background • Site 26 Record of Decision 1996 - GW Monitoring, Institutional Controls, and Extraction and Treatment of GW • COCs - PCE - VC - TCE - 1,2-DCA - Cis-1,2-DCE - 1,1-DCE • East-side Aquifer Treatment System (EATS) operational Jan. 1999 - July 2003 – Recovered <0.5 lbs/month of VOCs – Decreasing monthly recovery – Cost >$29,000 per lb of VOCs • EATS 5-year review noted that pump and treat may not be efficient, and recommended evaluating alternatives
  5. 5. East-side Aquifer Treatment System
  6. 6. EVALUATION OBJECTIVES
  7. 7. Evaluation Objectives • Per the 5-year Review evaluation of other clean-up alternatives • Developed Work Plan – Jan. 2003 • Work Plan activities divided into two phases – Phase I • Evaluate geology / aquifer hydraulics • Assess potential COC rebound • Evaluate plume stability • Groundwater sampling – Phase II • Conduct nutrient enhancement pilot test • Groundwater sampling
  8. 8. PHASE I
  9. 9. Evaluation of Geology
  10. 10. Evaluation of Geology Results - Cross Section A-A’
  11. 11. Well / Aquifer Testing • Performed recovery tests on each extraction well • Turned off wells one at a time. Measured water level responses in surrounding wells Results ● No response related to direction ● Consistent with a coarse sand to fine gravel
  12. 12. Rebound / Plume Stability
  13. 13. Rebound / Plume Stability TCE Concentration Extraction wells off as of July 2003
  14. 14. Rebound / Plume Stability EXW-2 Plume Interior Well
  15. 15. Rebound / Plume Stability WU5-18 Plume Boundary Well
  16. 16. Natural Attenuation • Geochemical indicators support NA process – Low levels of dissolved oxygen, dissolved hydrogen and the presence of methane (supports anaerobic conditions) – Degradation products present • Natural attenuation is occurring • Degradation rate slow
  17. 17. Natural Attenuation Breakdown Products
  18. 18. PHASE II
  19. 19. Enhanced Natural Attenuation (HRC® Injection) • Conducted nutrient enhancement (NE) pilot test • Injected Hydrogen Release Compound (HRC®) at two groundwater “hot spots” to evaluate the ability for NE to reduce VOCs
  20. 20. Enhanced Natural Attenuation HRC® Placement • Pilot test targeted two separate areas • HRC® injected Feb.-March 2005 • Injected 7 to 32 ft below ground surface • 81 injection points (36 at PS-1 and 45 at PS-2)
  21. 21. Enhanced Natural Attenuation Location of HRC ® Injections and Monitoring Wells Treatment System
  22. 22. Enhanced Natural Attenuation Sampling Schedule • 13 wells sampled 12 times over 18 months • Sampled chemistry monthly through Sept. 2005 then quarterly until Sept. 2006 • Analyzed for VOCs, lactate, and NA parameters • Sampled select wells for microbial parameters and specific dechlorinating bacteria. Sampled 5 times June 2005 – Sept. 2006
  23. 23. RESULTS
  24. 24. Extent of TCE Plume Over Time
  25. 25. Extent of CIS-1,2-DCE Plume Over Time
  26. 26. Extent of VC Plume Over Time
  27. 27. W7-10, Within PS-1 Area TCE Concentration vs. Time
  28. 28. EXW-2, Within PS-2 Area TCE Concentration vs. Time
  29. 29. Bacterial Analysis • Suitable native bacteria present for reductive dechlorination across entire site • Added substrate (HRC®) stimulated microbes in pilot test areas, reducing VOCs to less than 50 µg/L • HRC® had limited impact in pilot test areas where VOCs were less than 50 µg/L
  30. 30. SUMMARY, CONCLUSIONS, AND RECOMMENDATIONS
  31. 31. Summary • 1,2-DCA remained below the ROD cleanup standard of 0.5 µg/L, except at 2 wells • 1,1-DCE remained below the ROD cleanup standard of 6 µg/L, except at 1 well • Other COCs generally at low concentrations • Natural attenuation is taking place. Native bacteria for dechlorination are present • HRC® reduced VOC concentrations to < 50 µg/L in pilot test areas. HRC® not effective when concentrations of VOCs < 50 µg/L
  32. 32. Conclusions • Very low VOC concentrations remaining • No VOC rebound • Stable VOC plumes • Low potential risk
  33. 33. Recommendations Based on the plume stability, no contaminant rebound and low potential risk, the Navy recommends: – EATS remain turned off and on standby – Monitored natural attenuation (MNA) implemented for completing remediation of groundwater at site
  34. 34. Schedule • Prepared and submitted a Draft Completion Report – June 2007 • Final Completion Report – fall/winter 2007

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