SITE INFORMATION AND CORRESPONDENCE_1993-2003

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Draft Soils FS Memorandum -14- 14 September 1993 . DDRW, Sharpe 2C-Treatment--In Situ Volatilization: The vapor extraction system (VES) pilot study performed at DDRW, Sharpe has demonstrated that in-situ volatilization is effective at removing TCE from the vadose zone. We concur that implementation of full scale VES appears to be an effective, cost-efficient method to remove TCE and to prevent TCE contamination in soils from migrating into the ground water. Other issues to consider include: 1. Low soil permeability limits subsurface air flow rates and reduces process efficiency. 2. Heterogeneous soil conditions must be considered in system design since they may result in inconsistent removal rates. 3. Verification of remediation is difficult, but may best be assessed using soil gas instead of soil borings. 3A-Innovative--Low-Temperature Stripping: This alternative is acceptable, however, there is currently a moratorium on incinerator permits. Other issues to consider include: 1. Tightly aggregated soil or hardpan may result in incomplete devolatilization during heating. 2. Requires subsequent treatment of the recovered vapors (Remedial Technologies Applications Matrix For Base Closure Activities, CA Military Base Closure Environmental Committee, April 1993). 4A-Removal and Disposal--Offsite Landfill Disposal: This alternative is acceptable, however, it does not provide for a permanent solution, but instead transfers the contaminated soil to another location where it would no longer threaten water quality. Therefore, offsite disposal is not a preferred alternative for all contaminated soils. 5A-No Action: This alternative is unacceptable as it will not fully protect human health or the environment, including water quality. t. Appendices F and G have been mislabeled, and should be corrected. U. Volume II, Appendix A, Page A-2-20, Section 2.4.3, Soil Borings: This section states that' the locations of the seven soil borings are shown in Figure 2-5. This figure is missing from the report. V. Volume Il, Appendix A, Page A-2-21, Section 2.4.3, Soil Borings: The last paragraph of this section states that near Bldgs. 179, 180, 186, and 199, unidentified source areas of organic vapors in soil may exist. It also states that the existence of these source areas is supported, in part, by the large number of mission-related activities which reportedly occurred in the area. Three of the buildings mentioned in this statement, Buildings 179, 180, and 199 belong to the category of sites for which no sampling was conducted and no further action is recommended.