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EA Engineering,Science,0wo Technology EA Western Regional Operations <br /> 41 Latayene Circle <br /> Lafayette,CA 94549 <br /> Telephone:415-283-7077 <br /> Fax:415-283-3894 <br /> 12 January 1993 <br /> Harlin Knoll <br /> San Joaquin County Public Health Services <br /> Environmental Health Division <br /> 445 North San Joaquin Street <br /> Stockton, California 95202 <br /> RE: Installation of One Downgradient Monitoring Well and Two Air Sparging Wells, <br /> Former Exxon Retail Site 7-3942, 4444 North Pershing Avenue, Stockton, <br /> California <br /> Dear Mr. Knoll: <br /> As requested by Exxon Company, U.S.A., EA Engineering, Science, and Technology <br /> has prepared this letter work plan for the installation of an off-site groundwater <br /> monitoring well, as requested by San Joaquin County, and two on-site aquifer air <br /> sparging wells. The off-site well will be installed to delineate the downgradient extent of <br /> the dissolved hydrocarbons northeast of former Exxon RS 7-3942, between well MW10 <br /> and MWII. This well will also be used to monitor progress of the proposed <br /> remediation. Two air sparging wells will also be installed to inject air into the saturated <br /> soils believed to contain free phase hydrocarbons, below and downgradient of the former <br /> tank field. <br /> A groundwater monitoring well will be installed northeast of the site in the parking lot at <br /> the Chateau Convalescent Hospital, if a property access is granted. A proposed well <br /> location is shown in Figure lb. The well will consist of nominal 4-inch Schedule 40 <br /> PVC, blank and screened casing. The borehole will be drilled approximately 45 feet <br /> below ground surface (12 feet below the deepest depth to water measured in the past 45 <br /> years); screen will be placed such that 10 feet extends below and 10 feet extends above <br /> current static water. During drilling soil samples will be collected at 5-foot intervals to <br /> describe soil lithology and for chemical analysis. The samples will be analyzed for Total <br /> Petroleum Hydrocarbons as gasoline (TPH-g) by EPA Method 8015 and for benzene, <br /> toluene, ethylbenzene and xylenes (BTEX) by EPA Method 8020. The top of casing <br /> elevation of the well will be surveyed, relative to the other EA wells. The wells will also <br /> be developed, and groundwater samples will be collected and analyzed for TPH-g and <br /> BTEX. Well installation and groundwater sampling will be scheduled so that it can be <br /> coordinated with the next round of quarterly sampling. <br />