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ARCO Products Company 4 <br /> ARCO Service Station#4493,205 North Center Street.Stockton,CA July 7,1999 <br /> • Stockpiled Soil. Approximately two cubic yards of soil generated <br /> during the installation of the four wells was stockpiled onsite. One <br /> composite sample (4 sleeves to 1 sample) was collected from the <br /> stockpiled soil and analyzed for TPH-g, BTEX, MtBE and total lead. <br /> The soil was hauled by Dillard Environmental Services to Chem Waste <br /> Landfill in Kettleman City, CA on June 30, 1999. Stockpiled soil <br /> analytical data is presented in Table 3 and a soil disposal certificate is <br /> included as Attachment G. <br /> SUMMARY OF FINDINGS <br /> • TPH-g in soil had reported concentrations of 1.80 mg/kg and 1.56 <br /> mg/kg in soil samples MW-4@20'and MW-4@25', respectively. <br /> Benzene had a maximum concentration of 0.118 mg/kg (MW-4@25'). <br /> MtBE had reported concentrations of 0.345 mg/kg (MW-3@25') and <br /> 1.52 mg/kg (MW-4@20'). <br /> • TPH-g was reported in two wells at concentrations of 231 ppb (MW- <br /> 1) and 15,000 ppb (MW-4). Benzene was reported in two wells at <br /> concentrations of 1.35 ppb (MW-1) and 503 ppb (MW-4). MtBE was <br /> reported in monitoring wells MW-3 and MW-4 at concentrations of <br /> 7.06 ppb and 9,990 ppb. <br /> • TCE and PCE were reported as nondetect in all soil samples. <br /> Groundwater samples had reported concentrations of TCE and PCE as <br /> high as 433 ppb and 2.50 ppb, respectively. <br /> • February 16, 1999 groundwater monitoring data indicated that the <br /> depth to water was 13.35 feet bgs to 14.64 feet bgs and groundwater <br /> flow was to the east-northeast at 0.008 ft/ft <br /> CONCLUSIONS <br /> Based on the data collected during this assessment, groundwater downgradient of the <br /> former product islands has been impacted by gasoline hydrocarbons. The extent of the <br /> hydrocarbon plume in groundwater is undefined. Additional assessment should be <br /> performed to define the downgradient extent of the hydrocarbon plume. <br /> TCE was reported in groundwater samples from three of the four wells (MW-1, MW-2, <br /> and MW-3). These wells are located upgradient and crossgradient of the former USTs <br /> and pump islands. TCE was not reported in the groundwater samples from Well MW-4, <br /> located downgradient of the former USTs and pump islands, nor in any of soil samples <br /> collected from the borings at the site. This data suggests that the source of TCE in <br /> groundwater is offsite. <br /> 7G600-022-0244 notal/ <br />