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A Ms Lori Duncan Page 2 of 3 • included in Attachment A Prior to sampling, monitoring wells MW 1 through MW4 were purged of a minimum of three well casing volumes The physical parameters of temperature, pH and electrical conductivity were measured during the purging process Groundwater samples were collected after the physical parameters had stabilized The samples were placed into an ice chest cooled to approximately 4°C and transported to Argon Laboratories (FLAP #2359) under chain of custody protocol Well purge logs are included in Attachment A GROUNDWATER ANALYTICAL RESULTS Groundwater samples were analyzed for the presence of TPHg, BTEX, and oxygenated gasoline additives (including the lead scavengers 1,2-DCA and EDB) using EPA methods 8015M, 8020, and 8260, respectively No TPHg or BTEX were detected in either well MW3 or well MW4 for the third consecutive sampling event TPHg was detected in wells MWl and MW2 at concentrations of 440 parts per billion (ppb) and 640 ppb, respectively Benzene was detected in wells MW1 and MW2 at concentrations of 0 7 ppb and 6 8 ppb, respectively Ethylbenzene was detected in wells MW1 and MW2 at concentrations of 1 1 ppb and 5 4 ppb, respectively Toluene was detected only in well MWl, at 0 7 ppb No xylenes were detected in any site well Methyl tert butyl ether (MTBE) was detected in wells MW 1 and MW3 at concentrations of 13 and 4 1 ppb, respectively No other oxygenated gasoline additives or lead scavengers were detected In any site well Analytical results are summarized in Table 2 Attachment B contains laboratory reports and chain of custody documentation SUMMARY Groundwater levels beneath the site rose slightly since last monitored in June 2001 Dissolved petroleum hydrocarbon constituents decreased in well MW1, but increased slightly in well MW2 Only benzene, at 6 8 ppb in well MW 1, exceeded the State Maximum Contaminant Level (MCL, 1 0 ppb) in any site well MTBE was present in MW 1 at a level equal to the MCL of 13 ppb for MTBE RECONIlVIENDATIONS Based upon the groundwater data collected to date, Ground Zero recommends conducting one additional round of groundwater monitoring and sampling at the site to monitor changes in groundwater flow and contaminant concentrations If analytical results are consistent with previous site data, Ground Zero recommends the site be considered for closure as a low risk site San Joaquin County Public Health Services, Environmental Health Division (PHS/EHD) will be notified at least 48 hours prior to conducting any site work • G1Data1GROUNDZE1TuffBoy\Reports\QMR13QM2001 doe