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A Quarterly Monitoring and Sampling Report(Q 1 2001) 5 Ranch Market 23569 Santa Fe Road Riverbank C'aLforn�a Febrwiry 16 2001 The water samples were analyzed for TPHg, BTEX, oxygenates, 1,2-DCA, and EDB using EPA method 8260B Groundwater Analytical Results Historical and recent groundwater laboratory analytical results are summarized in Table 3 The highest TPHg concentration was detected in monitoring well MW-1 at 14,000 parts per billion (ppb) (Figure 5) The highest benzene, MtBE, and TBA concentrations were detected in monitoring well MW-1 at 3,000 ppb, 320 ppb, and 62 ppb, respectively TBA was also reported in MW-4 and MW-5 at concentrations of 14 and 5 7 ppb, respectively 1,2-DCA was reported in MW-4 and MW-5 at concentrations of 2 5 and 0 51 ppb, respectively No other oxygenates or EDB were reported above the laboratory detection limits in samples collected from the monitoring wells The water samples collected from domestic wells DW-1, DW-3, and DW-4 did not contain detectable concentrations of TPHg, BTEX, oxygenates, 1,2-DCA, or EDB Copies of the laboratory analytical reports and chain-of-custody manifests are included in Attachment 4 Conclusion Ten groundwater monitoring wells and three domestic water wells were sampled this quarter • Groundwater elevation raised an average 0 04 feet since November 2000 Referring to Table 3, a significant decline in the concentration of benzene, TPHg, and MtBE was observed in wells MW-2 and MW-3 that are centered about the former tank pit Conversely, the concentration of benzene,TPHg, and MtBE increased in MW-1 and MW-4, also centered about the former tank pit MW-6, located upgradient of the former USTs, MW-8, located cross gradient of the former USTs, and MW-9, located downgradient of the former UST, all were reported to contain decreased or non-detectable concentrations of TPHg, BTEX, oxygenates, 1,2-DCA, and EDB In the fourth quarter 2000, concentrations of dissolved hydrocarbons in ground water decreased in MW-1 through MW-4 and increased in penmeter wells MW-5, MW-6, MW-8, and MW-9 compared to concentrations observed in the third quarter 2000 Analytical data for the first quarter 2001 indicate a return to concentrations in all monitoring wells typical of historical levels observed in third quarter 2000 and previous quarters The fluctuation and subsequent rebound of concentrations in groundwater were due to the SVE/AS feasibility test conducted October 2000 Future Work Future work planned in the first and second quarter 2001 include the following tasks • Conduct 2nd quarter monitoring and sampling event • Preparation and issuance of the Final Remediation Plan for soil and groundwater remediation at the site • File Riverbank 01-1Q