SITE INFORMATION AND CORRESPONDENCE_1992

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r Work Plan Addendum -4- 21 September 1992 DDRW, Sharpe obtain soils gas data (page 5-5) . However, we are concerned that this method of analysis will result in false negatives as the retrieval of the sample for OVA measurement will cause excessive volatilization of the contaminated sample and will not provide contaminant specific measurements. In-situ soils gas data are far more representative of actual concentrations present in the unsaturated zone and are critical for optimal placement of the vapor extraction wells. In addition, Sharpe also proposes to use soil analytical data to estimate the efficiency of the VES. It is unclear why Sharpe proposes to use soil analytical data to assess a remedial action that is designed to extract the vapor phase of contamination. We believe that soils gas data are needed to appropriately assess the extent of the vapor phase contamination in the unsaturated zone. We continue to believe that soils gas data should be used to map the extent of VOC contamination in the unsaturated zone, as well as, to estimate the efficiency of the VES. Furthermore, we question whether the costs associated with laboratory soils analysis will exceed the costs for soil gas surveys over the long-term. 5. The Draft Work Plan states that additional investigative work in the area of UST No. 49 is unnecessary. PCBs were found at 12.0 ug/l in the ground water sample from MW-474A, which exceeds the Primary MCL of 0.5 µg/l . Sharpe's position for not conducting any additional investigation is supported by stating that the ground water, which contains PCBs, is being remediated because it is within the capture zone for the South Balloon ground water treatment system (GWTS) (page 2-6) . The treatment technology for the South Balloon GWTS is air stripping. This treatment technology is appropriate for VOCs, but is inappropriate for PCBs. Because the ROD for this investigation was postponed until 1994, there is additional time to assess and monitor for PCB contamination in soils and ground water. Additional investigation is needed not only in the area of UST No. 49, but also in the area of UST No. 27 where the highest concentrations of PCBs and heavy metals were found in ground water. Cleanup levels for PCBs and heavy metals will need to be established for the 1994 site-wide ROD, in addition to the selection of an appropriate remedial technology. In our National Pollutant Discharge Elimination System (NPDES) inspection of the Interim Remedial Measures (IRMs), conducted on 28 April 1992, we collected influent and effluent samples from both the North and South Balloon GWTS. PCBs were not detected in any of the samples. In the renewal of the NPDES permit, we will require monitoring of PCBs. However, Sharpe should be monitoring for PCBs prior to the renewal of the permit to assure that PCBs are not entering the IRMs and possibly causing operational problems. 6. It remains unclear if background concentrations for metals in soils and ground water, other than arsenic and possibly selenium, have been determined for the Sharpe site. If these data have been collected, Sharpe should summarize all of the background concentrations for each inorganic constituent in a table and reference the wells from which the samples were collected. In the Attachment, we have provided general guidance on the considerations for establishing soil and ground water cleanup levels, the methodologies for