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Mr Harlin Knoll Page 2 of 3 . northwest with a gradient of 0 001 ffft, or approximately 5 3 feet per mile A potentiometric surface map for January 6, 2004 is presented on Figure 2 Groundwater monitoring data are summarized in Table I Monitoring data sheets are included in Attachment A At least three well casing volumes of water were purged from monitoring wells MW 1 through MW7 before sampling Temperature, pH, and electrical conductivity were measured during the purging process Samples were collected after the measured parameters stabilized and water levels recovered to at least 80% of pre-purged levels Purged groundwater was contained in appropriately labeled DOT-approved 55-gallon drums, which are stored on site pending disposal Purge logs are included in Attachment A Groundwater samples were delivered under chain of custody protocol to Argon Laboratories (ELAP #2359) Samples were analyzed for the presence of TPHg using EPA method 8015B, BTEX using EPA method 8021B, and oxygenated gasoline additives including 1,2-DCA and EDB using EPA method 8260B 3.0 GROUNDWATER ANALYTICAL RESULTS Methyl-tert butyl ether (MTBE) was the only chemical of concern detected above laboratory method detection limits (MDLs) MTBE in site wells ranged from 0 8 parts per billion (ppb) in well MW2 to 88 ppb in well MW3 Analytical results are summarized in Table 2 Attachment B • contains laboratory reports and chain of custody documentation for groundwater samples collected in January 2004 4.0 SUMMARY AND CONCLUSIONS • Groundwater elevations at the site rose an average of 1 07 feet since last monitored in September 2003 Groundwater beneath the site flowed northwest at a gradient of approximately 5 3 feet per mile • No total petroleum hydrocarbons as gasoline (TPHg), total petroleum hydrocarbons as diesel (TPHd), or BTEX constituents have ever been detected above MDLs in any site well MTBE was the only chemical of concern detected during this sampling event • MTBE concentrations in groundwater exceeded the primary and secondary MCLS of 13 ppb and 5 ppb, respectively, in only one well (MW3) The estimated extent of MTBE in shallow groundwater beneath the site is illustrated on Figure 3 5.0 RECOMMENDATIONS The MTBE plume beneath the site has been defined and is decreasing in size and concentration Figure 4 presents a chart illustrating the decline in MTBE in site wells Ground Zero recommends that San Joaquin County Environmental Health Department (EHD) consider closing this site as a G IGROUNDZE\Bamyard-Manser%Reports\QMR1200314QM2003 doc