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.r� F <br /> 1f <br /> Subsurface Investigation December 12, 1990 <br /> Farmer Unocal Station No. 2859, Stockton, California AGS 38012-5 <br /> CONCLUSIONS <br /> } Based on the results of field investigations and laboratory analyses to date, Applied Geosystems <br /> concludes: <br /> o Soil with residual hydrocarbons beneath the former tanks has been removed by <br /> excavation to an approximate depth of 30 feet below grade. <br /> o Hydrocarbons remain in the soil near borings KB3 and KBS at approximately 20 <br /> feet below grade, but hydrocarbon concentrations are below detection limits for the <br /> methods used at 15 feet below grade in these two borings. Hydrocarbons were not <br /> detected in soil samples collected at 25 feet below grade in borings B-1 and B-3; <br /> therefore, we conclude residual hydrocarbons remaining in soil borings KB3 and <br /> KB5 has been delineated laterally. <br /> o The extent of hydrocarbons in soil is delineated to the north of tank cavity(boring <br /> r;3 r B-1), to the west of boring KB3 (boring B-3), to the east of pump islands (boring <br /> B-2) and south of boring KBS (boring B-ti). Hydrocarbons are not present in the <br /> soil near the offsite soil borings B-4 and B-5. <br /> o Soil with residual hydrocarbons remains in place near borings KB3 and I:B:,. <br /> o Concentrations of dissolved hydrocarbons have increased in recent monitoring <br /> events in well MVV-2. Initial laboratory results indicated the concentration of € <br /> dissolved hydrocarbons collected from wells MW-4 and MW-5 were below detection <br /> limits; however dissolved hydrocarbons have been detected in more recent <br /> monitoring events. <br /> o The extent of dissolved hydrocarbons in ground water is not delineated to the west <br /> and south of well MW-2. <br /> 21 <br /> APplled Ge®Systems <br />