Moffett EATS Evaluation Presentation to RAB July 12, 2007

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