SITE INFORMATION AND CORRESPONDENCE_1992

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Work Plan Addendum -8- 21 September 1992 DDRW, Sharpe were found in ground water samples, as well as elevated concentrations of benzene, toluene and xylene (BTX) , trichloroethylene (TCE) , 1,2-dichloroethane (DCA) and PCBs (exceeding the Primary MCL by two orders of magnitude) . One of the highest concentrations of lead and chromium in soil (484 mg/kg and 169 mg/kg, respectively) were found in the sample from WMU No. 26 investigation (page 4-7) . Because these two areas are adjacent and metals contamination by constituents other than chromium and lead are known, Sharpe should analyze for all Title 22 metals in the ground water samples collected from the four monitor wells in the area of WMU No. 26 and the additional monitor wells needed for the investigation of UST No. 27. 12. Sharpe intends to conduct two long-term VES pilot studies. One of the studies will be conducted again in SA8 in the South Balloon Area. However, rather than conducting the other long-term study in SA14 (the fire fighting training area) in the Central Area, Sharpe has elected to conduct it in SA15 in the North Balloon Area. It is unclear why SA14 was deselected and SA8 was retained, when the highest VOC ground water contamination (up to 20,000 µg/1 ) was found in Plume 6 in the Central Area. It is unknown if the relative soils gas concentrations between SA8 and SA14 were considered for the deselection of one of these two areas for the long term VES pilot study. 13. For the long-term (three month) VES pilot study, Sharpe intends evaluate the efficiency of the VES by measuring soils gas using a VOA and by collecting soil samples for laboratory analysis. The Work Plan Addendum does not appear to indicate whether VOC concentrations in ground water in the area of the long- term tests would be considered as part of the evaluation of the VES. VOC concentrations in ground water should be measured prior to, during and after the long-term VES pilot study to evaluate the interactions of the source area and ground water cleanups. We have previously written in our 17 April 1992 letter, regarding the need to evaluate ground water in the VES pilot study. 14. The Work Plan Addendum states that the information from the long-term VES pilot study will help to address the economic tradeoffs of VES versus ground water treatment (page 5-3) . This statement causes concern because it indicates that Sharpe intends to either perform cleanups of the unsaturated zone or the ground water. We believe that in-situ soils gas data must be contoured prior to the design of the VES. We also believe that cleanup using VES is critical for source removal , in addition to conventional pump and treat ground water cleanups because the VES will remediate the source area, which in turn, should reduce the length of time required for remediation of the ground water. 15. The Work Plan indicates that additional vapor extraction wells will be installed in SA8 in the South Balloon Area for the long-term VES pilot study. The Addendum does not indicate whether or not these new or existing vapor extraction wells will be used as passive wells. As previously written in our letter of 17 April 1992, passive vapor extraction wells should be used, depending on the plume configuration and soils gas distribution, as the efficiency of the VES may be improved by increasing air flow to the other vapor extraction wells. 16. Sharpe submitted a summary of existing data in Appendix A of the Work Plan Addendum. After briefly reviewing the data, I have the following comments.