SITE INFORMATION AND CORRESPONDENCE_1992

Home Browse Search

Draft Soils FS Report Memorandum -3- 17 April 1992 DDRW, Sharpe contamination and potential ground water impacts and to collect sufficient data to develop a soil cleanup level that is ground water protective. 6. The use of Designated Level Methodology (DLM) to determine the soil cleanup levels appears to be inappropriately used. The DLM was used to determine the cleanup level for trichloroethylene (TCE) but was not used to determine the soil cleanup level for metals, pesticides or total petroleum hydrocarbons (TPHs) . It is unclear why the DLM was used for determining the cleanup level for TCE when this constituent is also present in the vapor phase and when ground water has already been impacted. The DLM is more appropriately used for inorganics and long chain organics which tend to be immobile in soils and would more readily attenuate in the unsaturated zone. In addition, use of the DLM was selective and did not follow all of the guidelines or protocol described in the document. The guidance in the DLM to use soluble concentrations of contaminants to determine the total designated level (TDL) and to consider the additive affects of multiple contaminants was clearly ignored. The DLM should be used to determine cleanup levels for appropriate constituents, such as heavy metals, and all of the guidance should be followed. 7. The proposed soil cleanup level of 960 milligrams per kilogram (mg/kg) for lead is essentially the hazardous level for total concentrations (1000 mg/kg) . The proposed cleanup level for lead does not appear to consider protection of ground water quality and is therefore unacceptable. This cleanup level was proposed without evaluating the solubility of lead (i .e. , apparently analysis for soluble concentrations of lead has not been performed) or the presence of organic lead. For those WMUs and USTs which may have potential contamination by lead, additional soils samples need to be collected and analyzed for soluble concentrations and organic lead. 8. The proposed soil cleanup level of 0.5 mg/kg for TCE is unacceptable. This cleanup level is too high considering that ground water has already been impacted and the fact that soil samples alone are not representative of TCE in the unsaturated zone. Soils gas data are known to be orders of magnitude greater than the concentrations of TCE from soils samples. We have previously written regarding the use of soils gas data for soil remediation in our letter dated 24 July 1991. If the proposed remedial action of vapor extraction is either not implemented or is discontinued prematurely and these concentration remain in-place, then TCE may still continue to impact and degrade ground water quality. The soil cleanup level for TCE should be background concentrations. 9. The Draft Soils FS Report identifies only two areas of TCE contaminated soils (Figure 2.2-1) . The two identified sites are in the South Balloon area (Plume 1) and in the area of Plume 6. These sites have apparently been identified on only a portion of the soil borings data and do not consider soils contamination by TCE or other solvents in the vapor phase. Soils gas data should have been used for identification of contaminated soil sites. In addition, it is unclear why soils boring data (i .e. , dissolved phase contamination) has been used to identify the sites needing remediation when the preferred remedial action is vapor extraction. Use of only soil borings data, which represent the dissolved VOC contamination, will underestimate the volume of soils needing remediation and will not provide a basis for design of an effective vapor extraction system (VES) . This issue is discussed in more