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PUBLIC HEALTH SERVICES <br /> SAN JOAQUIN COUNTY <br /> ENVIRONMENTAL HEALTH DIVISION <br /> Karen Furst, M.D., M.P.H., Health Officer <br /> 304 East Weber Avenue,Third FIoor • Stockton, CA 95202 <br /> 2091468-3420 <br /> PAUL SUPPLE <br /> ARCO PRODUCTS COMPANY MAY 13 1998 <br /> P.O. BOX 6549 <br /> MORAGA, CA 94570 <br /> RE: ARCO Service Station 2186 SITE CODE: 1035 <br /> 3212 N. California St. <br /> Stockton, CA 95204 <br /> San Joaquin County Public Health Services Environmental Health Division(PHS/FHD) <br /> has reviewed the February 20, 1998 Quarterly Monitoring Report (QMR)prepared by <br /> EMCON and Associates for the above referenced site. <br /> Monitoring of the recently constructed Monitoring Well (MW)4 indicated tertiary <br /> butanol present at 190 parts per billion(ppb) in ground water. Benzene and other <br /> gasoline constituents were present in water from MW4 as well. Since sample results <br /> indicate contamination has migrated to MW4, the lateral extent of the plume is unknown. <br /> Records from soil sample analysis results on August 29, 1995 indicate total hydrocarbons <br /> as gasoline at 1.1 parts per million(ppm) at 56.5 feet below surface grade (bsg) in boring <br /> 1 (B-1) and 1.1 ppm at 56.5 feet bsg in B-3: benzene levels were .019 ppm at 56.5 feet <br /> bsg in B-I and .015 ppm at 56.5 feet bsg in B-3. Since data is not in evidence for any <br /> deeper soil sampling analysis, the vertical extent of the soil contamination has not been <br /> defined. Once the vertical extent of the soil contamination is defined PHS/EHD can <br /> evaluate whether the existing wells are intercepting the groundwater contaminant plume. <br /> In order to define the soil contamination vertically a soil boring should be drilled near <br /> MW 1 using the continuous core soil sampling technique. The boring should continue to <br /> at least 75 feet bsg (historical low level of groundwater for this area). Drilling and <br /> sampling should continue until PID and field observations indicate two consecutive five <br /> foot intervals of non detectable soil readings. Submit a work plan for this investigation <br /> by July 1, 1998. <br /> Conduct a survey of domestic, municipal, agricultural, industrial and other wells within a <br /> 2000 foot radius of this site. Contact the Department of Water Resources, municipal <br /> water suppliers and other sources, and conduct a door to door investigation as necessary <br /> to identify these wells. Provide the location and construction of these wells in the work <br /> plan. <br /> A Division of San Joaquin Counry Health Care Services <br />