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r f.- <br /> of the San Joaquin County Public Health Services makes no mention of whether any <br /> • action was taken regarding either of these events <br /> The first site investigation was performed in May and June of 1991 The investigation <br /> consisted of a review of available agency records, and collection of soil samples from nine <br /> soil borings in the vicinity of the tanks and across the site Analysis of soil samples indi- <br /> cated detectable petroleum hydrocarbons, TPH gasoline and BTEX, but no TPH diesel at <br /> depths predominantly from 25 to 27 feet below ground surface (bgs) across the site The <br /> soil - groundwater interface was also encountered at a depth of approximately 25 to <br /> 27 feet bgs. <br /> In January 1992, the fuel tanks were removed from the site The sample collected from <br /> beneath the southern end of the northernmost tank (the unleaded gasoline tank) at a depth <br /> of approximately 16 feet bgs contained 785 mg/kg (or parts per million, ppm) of TPH as <br /> gasoline Petroleum hydrocarbons were not detected in soil samples collected from <br /> beneath the diesel and leaded gasoline tanks, nor from beneath the northern end of the <br /> unleaded tank <br /> A preliminary site assessment was performed in November 1992 The work included a <br /> review of available agency records, installation of five, 2-inch-diameter groundwater moni- <br /> toring wells, and analysis of soil and groundwater samples from each boring/well Static <br /> depth to water was estimated to be approximately 30 5 feet bgs with a groundwater gra- <br /> dient toward the northeast Soil analyses detected petroleum hydrocarbons at depths of <br /> 25 and 30 feet in four of the five well borings No petroleum hydrocarbons were detected <br /> in any of the borings at depths of 15 to 20 feet In groundwater, trace concentrations of <br /> petroleum hydrocarbons and/or BTEX were detected in four of the five groundwater <br /> monitoring wells <br /> Quarterly groundwater sampling of the five onsite monitoring wells was performed in June, <br /> September, and December of 1993 Water levels rose four feet from a depth of approxi- <br /> mately 30 5 to 26 5 feet bgs between November 1992 and June 1993, saturating previ- <br /> • <br /> �Ob*N940549lreport eoc 2 940549 00 <br />