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Site 26 Evaluation
RAB PresentationFormer Naval Air Station Moffett FieldJuly 12, 2007
Presented by:Liz BarrNavy Remedial Project Manager
Presentation Outline
• Background • Evaluation Objectives
– Phase I– Phase II
• Results• Summary, Conclusions, and
Recommendations• Schedule
BACKGROUND
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
East-side Aquifer Treatment System
EVALUATION OBJECTIVES
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
PHASE I
Evaluation of Geology
Evaluation of GeologyResults - Cross Section A-A’
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
Rebound / Plume Stability
Rebound / Plume StabilityTCE Concentration
Extraction wells off as of July 2003
Rebound / Plume StabilityEXW-2 Plume Interior Well
Rebound / Plume StabilityWU5-18 Plume Boundary Well
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
Natural AttenuationBreakdown Products
PHASE II
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
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)
Enhanced Natural AttenuationLocation of HRC ® Injections and Monitoring Wells
Treatment System
Enhanced Natural AttenuationSampling 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
RESULTS
Extent of TCE Plume Over Time
Extent of CIS-1,2-DCE Plume Over Time
Extent of VC Plume Over Time
W7-10, Within PS-1 Area TCE Concentration vs. Time
EXW-2, Within PS-2 AreaTCE Concentration vs. Time
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
SUMMARY, CONCLUSIONS, AND RECOMMENDATIONS
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
Conclusions
• Very low VOC concentrations remaining
• No VOC rebound
• Stable VOC plumes
• Low potential risk
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
Schedule
• Prepared and submitted a Draft Completion Report – June 2007
• Final Completion Report – fall/winter 2007