The evaluation assessed the groundwater contamination plume at Site 26 and evaluated alternatives to the existing pump and treat system. Phase I found the plume was stable with natural attenuation occurring. Phase II tested enhanced natural attenuation through nutrient injection, which reduced VOC levels below cleanup standards in test areas. The evaluation recommends monitored natural attenuation to complete the groundwater remediation as plumes are stable with no rebound and risks are low.

1. Site 26 Evaluation
RAB Presentation
Former Naval Air Station Moffett Field
July 12, 2007
Presented by:
Liz Barr
Navy Remedial Project Manager

2. Presentation Outline
• Background
• Evaluation Objectives
– Phase I
– Phase II
• Results
• Summary, Conclusions, and
Recommendations
• Schedule

3. BACKGROUND

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. East-side Aquifer Treatment System

6. EVALUATION
OBJECTIVES

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. PHASE I

9. Evaluation of Geology

10. Evaluation of Geology
Results - Cross Section A-A’

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. Rebound / Plume Stability

13. Rebound / Plume Stability
TCE Concentration
Extraction wells
off as of July 2003

14. Rebound / Plume Stability
EXW-2 Plume Interior Well

15. Rebound / Plume Stability
WU5-18 Plume Boundary Well

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. Natural Attenuation
Breakdown Products

18. PHASE II

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. 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. Enhanced Natural Attenuation
Location of HRC ® Injections and Monitoring Wells
Treatment System

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. RESULTS

24. Extent of TCE Plume Over Time

25. Extent of CIS-1,2-DCE Plume Over Time

26. Extent of VC Plume Over Time

27. W7-10, Within PS-1 Area
TCE Concentration vs. Time

28. EXW-2, Within PS-2 Area
TCE Concentration vs. Time

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. SUMMARY,
CONCLUSIONS, AND
RECOMMENDATIONS

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. Conclusions
• Very low VOC concentrations remaining
• No VOC rebound
• Stable VOC plumes
• Low potential risk

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. Schedule
• Prepared and submitted a Draft
Completion Report – June 2007
• Final Completion Report – fall/winter 2007