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3246 East Fremont Street, Stockton, California September 16, 1993 <br /> Chevron USA Products Company Page 5 <br /> 3.e GROUNDWATER SAMPLING <br /> ' Prior to sampling, the three available wells (MW4, MW-5 and EA-6) were purged of approximately three <br /> ' well casing volumes or until pH, conductivity, and temperature of the purged groundwater had stabilized. <br /> Groundwater samples were collected using a Teflon sampler cleaned with detergent and distilled water. <br /> Prior to sampling, a distilled water rinsate sample was collected from the teflon sampler to document the <br /> cleanliness of the sampler. In addition, distilled water travel blanks were collected to document ambient <br /> sampling and transport conditions. Each sample was placed on ice in an insulated container for delivery <br /> to a State-certified laboratory. The samples were accompanied by a chain-of-custody manifest during <br /> transport and analyzed for BTEX and TPH-G by EPA methods 5030%8020/modified 8015. Purge water <br /> ' generated during the sampling process was stored in a DOT-approved purge water trailer and <br /> transported to the Chevron refinery in Richmond, California for recycling. <br /> 4.0 SITE CONDITIONS <br /> ' 4.1 HYDROGEOLOGY <br /> ' The site is located in the northern part of the San Joaquin Valley at approximately 25 feet above sea <br /> level. The shallow subsurface stratigraphy beneath the site consists mostly of silty clays with <br /> ' interbedded layers or lenses of sandy clay. At approximately 24 to 32 feet and 48 to 80 feet are zones <br /> of poorly sorted sand. During drilling, groundwater was encountered between 75 and 76 feet BG. <br /> ' Historical and recent groundwater monitoring data are summarized in Table 2. Figure 3 is a <br /> potentiometric surface map constructed from groundwater monitoring data collected June 28, 1993. The <br /> ' map indicates that groundwater beneath the site flows to the southwest at a hydraulic gradient of 0.009. <br /> 4.2 ANALYTICAL RESULTS FOR SOIL <br /> Laboratory analytical results for soil samples collected May 3 and 4, 1993 are summarized in Table 1. <br /> Sail samples collected from MW-5 and beneath the former product lines were below the method <br /> detection limits for BTEX and TPH-G. Benzene was below the method detection limit in all analyzed soil <br /> GROU NDWATER <br /> ' ss�a RRr ��� 'TECHNOLOGY <br />