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E C 0 R Mr Michael Infurna— SJCEHD March 13, 2003 Page 5 samples were collected directly from a spigot at the holding tank DW-2R, DW-3, and DW-4 are sampled quarterly, and DW-1 is sampled monthly Groundwater Sampling Procedures The groundwater monitoring wells were re-monitored to verify at least 80% recovery prior to sampling Adequate recovery was observed in the purged wells prior to sampling A disposable bailer was used to collect the groundwater samples All samples were collected in appropriate containers, preserved on ice, and transported under chain-of-custody manifest to Kiff Analytical LLC located in Davis, California The water samples were analyzed for TPHg, BTEX, 1,2-DCA, EDB, and five oxygenates using EPA method 8260B Per the RWQCB written request, the water samples collected from wells MW-5, MW-5D, MW-6, and MW-9 were also analyzed for dissolved metals using EPA Method 200 8 Groundwater Analytical Results Historical and recent groundwater laboratory analytical results are summarized in Table 3 The highest benzene and TPHg concentrations were detected in MW-3 at 12,000 ppb and 180,000 ppb, respectively (Figure 5) The highest MtBE concentration was detected in monitoring well MW-4 at and 120 ppb Other oxygenates were not detected above the laboratory reporting limits in samples collected from the monitoring wells Well AS-1, located within the source area and screened from 40 to 45 feet bgs, was sampled for the third time Benzene and TPHg were detected at 17 ppb and 250 ppb, respectively Toluene, ethylbenzene, xylenes, and oxygenates were not detected above the laboratory reporting limits (Table 3) The dissolved metal concentrations from wells MW-5, MW-5D, MW-6, MW-7 and MW-9 will be compared with future dissolved metal concentrations in order to monitor the effects of the ozone sparge remedial system (Table 4) Domestic Well Analytical Results The water samples collected from domestic wells DW-2R and DW-4 sampled quarterly did not contain detectable concentrations of TPHg, BTEX, oxygenates, 1,2-DCA, or EDB DW-3 was not sampled due to access restrictions DW-1 was sampled on January 10 and February 5, 2003 and all concentrations were reported as nondetect Copies of the laboratory analytical reports and chain-of- custody manifests are included in Attachment 4 Conclusions Nine of the ten groundwater monitoring wells, one air sparge well, and three of the four domestic water wells were sampled this quarter Wells MW-7 and DW-3 were not sampled due to access limitations Groundwater elevation increased by an average 1 67 feet since October 2002 Perimeter wells MW-8 and MW-9 did not contain benzene, TPHg, or MtBE above laboratory reporting limits this quarter It appears that the initiation of ozone sparge activities has caused mixing to occur within the water column because the source area AS-1 screened approximately 10 feet below the water table from 40 to 45 feet bgs contained benzene and TPHg above laboratory reporting limits this quarter Riverbank-03-1 Q doe SECOR lntemahonal Incorporated a i a 4