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� A Mr Jeff Wong Apnl 19, 2001 Page 2 of 4 groundwater depression was inferred near well MW4 A potentiometnc surface map generated using the February 2, 2001 monitoring data is presented on Figure 2 The calculated hydraulic gradient in the western portion of the site was approximately 0 0033 ft/ft The apparent groundwater depression in the eastern portion of the site suggests that the shallow aquifer is being influenced by pumping in the water supply well, or that some vertical leakage of the shallow aquifer is occurring through the water supply well Groundwater monitoring data are summarized in Table 1 and field data sheets are included in Attachment A Prior to sampling, monitoring wells MW 1 through MW9(B) were purged of at least three well casing volumes During the purging process the physical parameters of temperature, pH and electrical conductivity were measured Samples were collected after the physical parameters stabilized and water levels in the wells recovered to at least 80% of their initial levels Purged groundwater was contained in appropriately labeled DOT-approved 55-gallon drums, which are currently stored on-site Purge logs are included in Attachment A Groundwater samples were delivered udder chain of custody protocol to Argon Laboratories (FLAP #2359) for analysis of TPHg by EPA method 8015M, BTEX by EPA method 8020, and oxygenated gasoline additives, including the lead scavengers EDB and 1,2-DCA, by EPA method 8260B Samples collected from well MW9(B) were also sent to A&L Western Agricultural Laboratory (FLAP #1657) for analysis of nitrate and nitnte utilizing EPA method 353 2 Domestic Well Sampling At the request of San Joaquin County Public Health Services, Environmental Health Division (PHS/EHD), an experienced Ground Zero technician collected groundwater samples from three nearby domestic wells located east of the subject site after written authorization was received from the respective property owners Samples were analyzed by Argon Laboratories for gasoline constituents TPHg, BTEX, oxygenated gasoline additives, 1,2-DCA, and EDB No targeted analytes were detected in the samples collected from the domestic wells To date, eight groundwater samples have been collected from the nearest domestic wells located north and east of the subject site No constituents of concern have been detected in any sampled domestic well Analytical results have been submitted to PHS/EHD under separate cover GROUNDWATER ANALYTICAL RESULTS Elevated levels of dissolved gasoline constituents were detected in shallow monitoring wells MW 1, MW2, MW3, MW4, and MW6 TPHg in these wells ranged from 2,600 parts per billion (ppb) in well MW6 to 160,000 ppb in well MW1, benzene ranged from 19 ppb (MW6) to 3,200 ppb (MW1), and MTBE ranged from <2 0 ppb (MW2) to 20,000 ppb (MW4) No gasoline constituents were detected in shallow monitoring wells MW5, MW7, or MW8 The estimated extent of benzene and • MTBE in the shallow aquifer are presented in Figures 3 and 4, respectively No TPHg, benzene, or MTBE were detected in the deeper monitoring well MW9(B), although toluene G 1DaFa1GROUNDZEITULEBURG\Report QMRI1QM200E doe