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BACKGROUND/SUMMARY Soil contamination was documented following the removal of three underground storage tanks (USTs) from the site in January, 1991. Subsequent soil and groundwater investigations were undertaken to determine the extent of contamination. Two source removal excavation actions succeeded in removing all residual soil contamination. Very minor groundwater impact (benzene at appx. 1 ppb or less, TPHg non-detect to appx. 200 ppb) was detected in the initial samples collected in 1991 from monitoring well MW1. This well was installed within the former tankpit excavation. Subsequent sampling of the well in 1992 and 1993 resulted in reported concentrations of toluene, ethylbenzene and xylenes ranging from non-detectable to below 10 parts per billion (ppb) with no associated benzene or detectable TPHg. Groundwater sampling in 1993 from a hydropunch boring located downgradient of MW1 did not detect any contaminants. Following the completion of the hydropunch investigation, PHS/EHD concluded that all appropriate response actions had been completed and that no further investigation or remediation would be required. In a letter dated 8/12193, PHS/EHD recommended case closure to the CVRWQCB. In a response dated 9/22193, the CVRWQCB asked for a water supply well survey and an explanation of the method used to determine groundwater gradient prior to their consideration of the case for closure. This information was provided in a report prepared by RESNA dated 12120/93. PHS/EHD responded (1/19/94) by requesting the installation of at least two additional monitoring wells at the site. Further clarification of the validity of gradient determination was subsequently provided to PHS/EHD and it was agreed that two additional rounds of groundwater sampling would be sufficient to confirm the lack of groundwater impact. Recently, two consecutive rounds of groundwater sampling from MW 1 did not detect contaminants in groundwater beneath the site. Information on site geology and hydrogeology, nearby well locations and construction as well as tabulated analytical data are contained in the reports included as Attachment A. Agency correspondence is included as Attachment B. INVESTIGATION Soil In March 1991, source removal excavation was conducted in the former tank pit. Following the completion of excavation, fourteen soil samples were collected from the walls and floor of the pit and the pit was backfilled. The samples were analyzed for TPHg, total petroleum hydrocarbons as diesel - (TPHd) and BTEX. Several samples were reported to contain elevated concentrations of analytes, which indicated that soil contamination remained near the middle of the former 10,000 gallon UST and beneath the center of the former 500 gallon UST. i 2