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r 4 CONCLUSIONS Based on data collected to date, it appears that the Texaco Station has impacted the vadose zone from 15 to approximately 30 feet bgs near the eastern dispenser island. Based on soil samples collected from ARCO well MW-6, it appears that an off-site source (possibly the Transmission Store, through improper disposal of waste oil) has impacted the vadose zone west of the ARCO site (see Figures 2 through 4). Based on current isoconcentration maps, the highest concentrations of dissolved hydrocarbons are located adjacent to the Transmission Store and near the eastern dispenser island of the Texaco Station. Based on groundwater data, the groundwater flow has generally been to the northeast, therefore placing the ARCO Station downgradient of both the Texaco Station and the Transmission Store. Based on data collected to date, it is EMCON's opinion that dissolved gasoline hydrocarbons and volatile organic compounds in the groundwater, as well as gasoline hydrocarbons in soil beneath the site (below 25 feet), have migrated beneath the ARCO Station from the Texaco Station, Transmission Store, and perhaps from other sites not currently in the SJCPHS Leaking Underground Fuel Tanks Program. On this basis, it is EMCON's opinion that no additional assessment of soil and groundwater is warranted,_ and remediating by ARCO should be limited to on-site hydrocarbons present in soil above 25 feet bgs. We recommend that ARCO allow use of on-site vapor extraction welly to assist identified responsible parties in remediating groundwater and soil beneath the ARCO site. ARCO has authorized EMCON to conduct an additional assessment near the tank cavity. The additional assessment will consist of installing two vapor extraction wells and drilling a soil boring beneath the tank cavity. SAC,N.\PJM805�08051460.2AS-94\pas:1 Rev.0.5/5/95 0805-146.02 4-1