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n{ p Nts Vicki McCartney Page 2 of 3 After groundwater parameters bad stabilized and water levels had recovered to at least 80% of pre-purged levels, groundwater samples were collected using dedicated disposable bailers and transferred into appropriate containers The samples were stored in an ice-chest refrigerated to approximately 4°C, for subsequent transport to Argon Laboratories (ELAP 42359) under chain of custody protocol Field notes and purge logs are included in Attachment A GROUNDWATER ANALYTICAL RESULTS Argon Laboratories analyzed all groundwater samples for total petroleum hydrocarbons as gasoline (TPHg) using EPA method 801513, for benzene, toluene, ethylbenzene, xylenes (BTEX) using EPA method 8021B, and for oxygenated gasoline additives, including the lead scavengers EDB and 1,2-DCA, using EPA method 8260B Wells MW 1 and MW3 contained TPHg at 310 parts per billion (ppb) and 150 ppb, respectively Very low levels of benzene, toluene, ethylbenzene, and xylenes were also detected in well MW 1 No BTEX or oxygenated gasoline additives were detection in wells MW2 or MW3 Groundwater analytical results are summarized to Table 2 Laboratory reports are included in Attachment SUNEVIARY AND CONCLUSIONS • The depth to groundwater beneath the site ranged from 11 57 to 12 08 feet btoc Groundwater flowed . north with a gradient of approximately 26 feet per mile • TPHg was detected in wells MW 1 and MW3 at 310 ppb and 150 ppb, respectively I • Minor concentrations of benzene, toluene, ethylbenzene and xylenes were detected in well MWl at levels below their respective primary Maximum Contaminant Levels (MCLS) • No benzene, MTBE, or any other gasoline constituents were detected in wells MW2 or MW3 RECOMMENDATIONS Ground Zero recommends that San Joaquin County Environmental Health Department (EHD) consider closing this site as a low-risk groundwater contamination case based upon the following • The current levels of gasoline constituents in site wells remain below applicable primary MCLS • No oxygenated gasoline additives, including MTBE, has ever been detected in any site well, • The nearest known active water supply well is located approximately 1,100 feet upgradient of the site and is screened from depths greater than 340 feet(Ground Zero, August 23, 2002) _ • The primary and secondary contamination sources have been removed in the form of UST removal and overexcavation v GIGROUNDZEISouza\Reportsl2QMR_2003 due