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� n Project No 58080-06-02 May 5, 1995 ' inotor vehicle fuel to the environment beneath the site The known location of the former Douglas Oil USTs coincides with the previous highest petroleum hydrocarbon concentration in soil beneath ' the southwest portion of the site(11,000 mg/kg of TPHg detected at a depth of 25 feet bgs in boring " EB-11) This portion of the site was subject to soil vapor extraction remediation between June 1993 ' and March 1994 Soil collected from boring DTB-1, located approximately two feet east of boring EB-11, exhibited non-detectable levels of BTEX, TPHg and TPHd in April 1994 The highest ' concentrations of petroleum hydrocarbons detected beneath the northern portion of the site are located in the vicinity of a motor vehicle fuel dispensing system which may have been operated between approximately 1926 and 1957 Data indicates that the sources of the BTEX, TPHg and TPHd present in soil were the former USTs previously operated at the site ' 44 Sources of Groundwater Impacts The absence of detectable concentrations of MTBE in soil beneath the site combined with data indicating that MTBE exists in groundwater beneath and upgradient of the site suggests that the ' source of MTBE in groundwater is from an offsite location Immediately north of the site exists a formerly active Exxon service station that has been dispensing motor vehicle fuels with the MTBE ' additive since MTBE was introduced in Northern California in the early 1980's The Exxon service station, which was closed and fenced during the first quarter of 1995, may be the source of the ' MTBE in groundwater ' Reported gasoline and/or diesel fuel range hydrocarbons exist in groundwater at locations beneath the northern/central portion of the site (MW-3), beneath the southwest portion of the site (MW-1) ' and at upgradient and crossgradient locations MW-5 and MW-4, respectively The absence of detectable TPHg and TPHd in onsite downgradient well MW-2, combined with the knowledge that ' detectable TPHg and/or TPHd exist in groundwater at distances in excess of 100 feet in upgradient and crossgradient directions from the former USTs, suggest that the reported petroleum hydrocarbon impacts to groundwater beneath and in the vicinity of the site are from offsite locations These -23- 1