SITE INFORMATION AND CORRESPONDENCE_1992

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Work Plan Addendum -3- 21 September 1992 DDRW, Sharpe mix area investigation, additional soil samples will be collected to better define the lateral extent of pesticide contamination north and south of the ditch. In the investigation of WMU No. 26 for lead and chromium contamination, approximately ten percent of the field screened in-situ samples will be collected for laboratory analyses. The Work Plan Addendum does not indicate whether the soil samples will be analyzed for soluble concentrations of these contaminants using the Waste Extraction Test (WET) modified for deionized water. Soluble concentrations are needed to determine if the contaminants remaining in the soil will pose a threat to the environment (specifically, water quality) . Most of the existing soils data is for totals concentrations. Sharpe may be able to use these data to determine if the contaminant concentrations pose a threat to the environment by one of two methods which are described below. a. Collect the new samples and analyze for total and soluble concentrations. For each contaminant of concern, a ratio between total and soluble concentrations may be developed and used to back calculate soluble concentrations from the existing total concentration data. b. Assume that 100 percent of the total concentrations are soluble. Using the existing data, back calculate the soluble concentrations. The latter method is not preferred to back calculate soluble concentrations from total concentrations because it does not represent field conditions and is generally over estimates the in-situ soluble concentrations. 3. The Work Plan Addendum establishes cleanup levels for PCBs, total petroleum hydrocarbons (TPHs) and metals, specifically lead and chromium (pages 2-14 and 4-6) . The Work Plan is not the appropriate document to establish cleanup levels, but should be proposed in the FS. The proposed cleanup levels are as follows: Contaminant Cleanup Level Concentration PCBs 1 mg/kg TPHs 100 mg/kg Lead 200 mg/kg Chromium 500 mg/kg The Work Plan Addendum did not provide adequate justification for these proposed cleanup levels to assure that these concentrations, if left in-place will not leach and threaten water quality. The cleanup levels for TPH, lead and chromium are unacceptable. Of particular concern, is the proposed cleanup level for chromium because 500 mg/kg is the hazardous level for hexavalent chromium. Hexavalent chromium is considered to be relatively mobile. It is unknown whether or not the chromium contamination at the site is in a hexavalent form. We have previously expressed this concern in our 17 April 1992 letter. 4. Sharpe has attempted to address our concerns regarding the use of soil gas data to evaluate the extent of VOC contamination in the unsaturated zone. These concerns were previously discussed in our letters dated 24 July 1991 and 17 April 1992. Sharpe now proposes to use an organic vapor analyzer (OVA) to