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a nssocinres INC . Monitoring well MWI was purged a minimum of three well volumes and until the stabilization of electric conductivity, pH, and temperature was observed. Subsequent to purging, groundwater was sampled and transferred to appropriate sample containers, using a clean, disposable bailer with a bottom-emptying device to reduce volatilization. Sample containers were then labeled with sample identification, placed on ice, and shipped under chain-of-custody to Sequoia Analytical. Field development/purge logs are presented in Attachment 1. Laboratory Analysis The groundwater sample from well MW1 was analyzed by Sequoia Analytical for total petroleum hydrocarbons as gasoline (TPHg), benzene, toluene, ethylbenzene, and xylenes (BTEX) by EPA Methods 801518020, and oxygenate fuel additives by EPA method 8260. Laboratory Results TPHg and BTEX were detected above the laboratory method detection limits. No other gasoline constituents or oxygenate fuel additives were reported above their respective laboratory method detection limits. . Analytical results are summarized in Table 2. Laboratory data sheets and chain-of-custody documentation are provided in Attachment 2. WELL SURVEY ATC reviewed PHS/EHD groundwater well construction logs, Department of Water Resources (DWR) groundwater well construction logs, and conducted a site walk in the vicinity of the site to identify any groundwater wells located within 2,000-foot radius of the site. The search revealed that at least seven wells are potentially located within approximately 2,000 feet of the site. The wells were located on the map according to "well location" description information provided on the well construction logs. Of the wells identified in our search, none are located within 500 feet of the site. The approximate well locations and construction details are incorporated in Table 3 and Figure 3, respectively. In order to assess probable impacts from the site to nearby wells, ATC reviewed regional groundwater gradient data. Based on San Joaquin County Flood Control & Water Conservation District groundwater data, region groundwater flow is easterly (Fall 1997). Six of wells revealed in the wells survey (Figure 3, Well ID No. 1) are located in the inferred downgradient direction from the site. These wells are identified in well logs as groundwater monitoring and/or extractions wells and appear to be associated with an unauthorized petroleum . release from an underground storage tank. Well logs identify the site as an Exxon gasoline service station located at 4444 Pershing Ave., Stockton, California. Although these wells are not considered a source of drinking water, they have been included in ATC's well survey data. WA 17292.00021reportsl3 gmr2000.doc 2