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Mr Harlin Knoll Page 2 of 3 Monitoring wells MW1, MW2, MW3, MW4, MW5, and MW8 were purged a minimum of three well casing volumes of water and sampled on August 6, 2001 During the purging process temperature, specific conductance, and pH of the water were measured and recorded Groundwater samples were collected after the physical parameters stabilized and placed in an ice chest cooled to a temperature of at approximately 4°C for transport to Argon Laboratories (ELAP #2359) under chain of custody protocol The samples were analyzed for the presence of TPHg and BTEX utilizing EPA methods 8015M and 8020, respectively Purged groundwater was contained in labeled Department of Transportation (DOT) approved drums pending disposal Copies of field purge Iogs and water level measurements are included in Attachment A Groundwater Analytical Results Elevated levels of dissolved gasoline constituents were detected in the groundwater sample collected from well MW5 and low levels were detected in the sample collected from well MW 1 TPHg and BTEX constituents were not detected in the samples collected from wells MW2, MW3 MW4 or MW8 Well MW5 contained TPHg at a concentration of 35,000 parts per billion (ppb), benzene at 4,100 ppb, toluene at 860 ppb, ethylbenzene at 300 ppb, and xylenes at 2,600 ppb Well MW1 contained TPHg at a concentration of 180 ppb, benzene at 2 5 ppb, ethylbenzene at 3 2 ppb, and xylenes at 0 7 ppb Analytical results are summarized in Table 3 Laboratory data sheets and chain of custody documentation are included in Attachment B Figure 3 presents a benzene isoconcentration map from the most recent analytical results and Attachment C contains graphical representations of TPHg and benzene concentrations over time in site wells Well Destruction Activities On September 25, 2001, Mr Sean Garvey of Ground Zero and Mr Harlin Knoll of San Joaquin County Public Health Services, Environmental Health Division (PHS/EHD) observed Spectrum Exploration, Inc (Spectrum, C57-512268) destroy wells MW6, MW7, and MW8 The wells were destroyed pursuant to the August 9, 2001 workplan prepared by Ground Zero, which was approved by Mr Knoll A letter report detailing well destruction activities was submitted to PHS/EHD under separate cover CONCLUSIONS AND RECOMMENDATIONS • Concentrations of dissolved TPHg and BTEX in wells MW1 and MW5 have been gradually declining since their recorded highs BTEX constituents in well MW5 have declined by 90-97% since December 1996 Contaminant concentrations in well MW1 have decreased more than 97% from the recorded highs in that well • The consistently low levels of petroleum hydrocarbon constituents detected in well MW 1 coupled with the absence of contaminants in wells MW4 and MW2 suggest that well MW 1 is located at the approximate southeastern extent of the dissolved contaminant plume Knowles h-m/reports/3gm2001 doe