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'n/ La that will facilitate site closure. Because benzene is the only aromatic that exceeds drinking water standards, it is the focus of this investigation. It is suspected that the source of the aromatics is the Tank #3 vicinity. This is V indicated by soil samples containing aromatics (toluene) detected down to the water table in a boring advanced near Tank #3. However, the monitoring wells that have had detectable concentrations of aromatics are also located downgradient of Tanks #1 and #21 in addition to being adjacent to Tank #3. Previous sampling efforts in the Tank #1 and #2 area appear to be poorly documented, and there is the possibility that previous soil samples were collected from too shallow of a depth to detect whether a release had La occurred from these tanks. The Tank #4 vicinity is not considered a potential source of aromatics because aromatics have not been detected in the water samples from wells in this vicinity (MW-3 and MW-5) nor have they been consistently detected in the soil samples collected in this vicinity following the soil excavation. 4.0 PROPOSED SCOPE OF WORK A soil gas and soil investigation will be conducted to 1) investigate whether the Tank #1 and #2 vicinity is a potential source area, and 2) to evaluate the lateral and LA vertical extent of aromatics and TPH in the vadose zone. A survey of production wells for municipal, domestic, industrial, and other uses within 2,000 feet of the site is required 0-4 for site closure (Tri-Regional Guidelines, Appendix B) and does not appear to have been performed to date. Such a survey is proposed in this work scope to facilitate site closure. L4 In addition, it is proposed that a level survey be conducted to establish an accurate top- of-casing reference elevation for MW-4. V The soil gas study will consist of collecting soil gas samples from approximately 8 to 10 locations. The proposed soil gas sampling locations are shown on Figure 3. Actual R4182OA-625960-4 y soilvap2.pin 4