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EA Engineering,Science,aA.rfechnology ..J EA Western Regional Operations <br /> 41 Lafayette Circle <br /> Lafayette,CA 94549 <br /> Telephom 510-283-7077 <br /> Fax:510-283-3894 <br /> 3 February 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, California <br /> Dear Mr. Knoll: <br /> As requested by Exxon Company, U.S.A., EA Engineering, Science, and Technology has <br /> prepared this letter work plan for the installation of an off-site groundwater monitoring <br /> well, as requested by San Joaquin County, and two on-site aquifer air sparging wells. The <br /> off-site well will be installed to delineate the downgradient extent of the dissolved <br /> hydrocarbons northeast of former Exxon RS 7-3942, between well MW 10 and MW l 1. <br /> This well will also be used to monitor progress of the proposed remediation. Two air <br /> sparging wells will also be installed to inject air into the saturated soils believed to <br /> contain free-phase hydrocarbons, below and downgradient of the former 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 50 feet <br /> below ground surface (10 feet below the deepest depth to water measured in the past <br /> 45 years); screen will be placed such that 10 feet extends below and 10 feet extends <br /> above current static water. During drilling soil samples will be collected at 5-foot <br /> intervals to describe soil lithology and for chemical analysis. The samples will be <br /> analyzed for Total Petroleum Hydrocarbons as gasoline (TPH-g) by EPA Method 8015 <br /> and for benzene, toluene, ethylbenzene and xylenes (BTEX) by EPA Method 8020. The <br /> top of casing elevation of the well will be surveyed, relative to the other EA wells. The <br /> wells will also be developed, and groundwater samples will be collected and analyzed for <br /> TPH-g and BTEX. Well installation and groundwater sampling will be scheduled so that <br /> it can be coordinated with the next round of quarterly sampling. <br /> VMENS c>!'� ��4 <br /> Pp <br /> R�gE161g99 Tv <br /> gP 0NEP j STNp�vS`()N X23 <br /> Q ER <br /> pUBti\BENZ <br /> ENV\1111 <br />