ARCHIVED REPORTS_THIRD QTR 2003 - Laserfiche WebLink

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�1 1' Mr Harlin Knoll Page 2of3 . with an average gradient of 0 0027 ft/ft, or approximately 14 feet per mile A potentiometric surface map for September 30, 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 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 were stored on site pending disposal Purge logs are included in Attachment A Groundwater samples were delivered under chain of custody protocol to Argon Laboratories (FLAP #2359) Samples were analyzed for the presence of TPHg using EPA method 801513, 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 laboratory method detection limits (MDLs) MTBE was detected in all site wells, ranging from 0 8 parts per billion (ppb) in well MW7 to 86 ppb in well MW3 Analytical results are summarized in Table 2 iAttachment B contains laboratory reports and chain of custody documentation for groundwater samples collected in September 2003 4 0 SUMMARY AND CONCLUSIONS • Groundwater elevations at the site fell an average of 1 76 feet since last monitored in June 2003 Groundwater beneath the site flowed west at a gradient of approximately 14 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 • I 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\GROUNDZF\Barnyard-ManserlReports\QMR1200313QM2003 doe