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Mr Harlin Knoll Page 2 of 3 • 0 0025 ft/ft, or approximately 13 feet per mile A potentiometnc surface map for June 26, 2003 is presented on Figure 2 Groundwater monitoring data are summarized in Table 1 Monitoring data sheets are included in Attachment A At least three well casing volumes of water were purged from monitoring wells MW1 through MW7 before sampling Temperature, pH, and electrical conductivity were measured dunng the purging process Samples were collected after the measured parameters stabilized and water levels recovered to at Ieast 80% of pre-purged levels Purged groundwater was contained in appropriately labeled DOT-approved 55-gallon drains, which were stored onsite 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 8015M, 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-tent butyl ether (MTBE) was the only chemical of concern detected above laboraton, method detection limits (MDLs) Wells MW3 and MW5 contained MTBE at concentrations of S100 parts per billion (ppb) and 4 5 ppb, respectively No MTBE was detected above MDLs in wells MW I, MW2, MW4, MW6, or MW7 Analytical results are summarized in Table 2 The estimated extent of MTBE in shallow groundwater beneath the site is illustrated on Figure 3 Attachment B contains laboratory reports and chain of custody documentation for groundwater samples collected in March 2003 4 0 SUMMARY AND CONCLUSIONS • Groundwater elevations at the site rose approximately one foot since last monitored in March 2003 Groundwater beneath the site flowed west at a gradient of approximately 13 feet per mile • Total petroleum hydrocarbons as gasoline (TPHg), total petroleum hydrocarbons as diesel (TPHd) and BTEX constituents have never 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 MCL of 13 ppb only in well MW3 5.0 RECOMMENDATIONS • The MTBE plume beneath the site has been generally defined, and is decreasing in size and concentration Ground Zero recommends that San Joaquin County Environmental Health Department (EHD) consider closing this site as a low-risk groundwater contamination case G IGROUNDZE\Barnyard-ManserlReportslQMR1200312QM2003 doc