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al X11
<br /> Quarterly Monitonng and Sampling Report(Q4 2000) 4
<br /> Ranch Market 23569 Santa Fe Road Riverbank Cali onu l December 19 2000
<br /> • Groundwater Sampling
<br /> Well Purging
<br /> On November 16, 2000, groundwater monitoring wells were purged using a submersible pump
<br /> and disposable bailers until pH, temperature, and conductivity readings had stabilized
<br /> Temperature, conductivity, and pH readings were recorded in the ten wells, at regular purge
<br /> intervals of one casing volume, with a portable instrument that was calibrated before the wells
<br /> were purged Water purged from the ten groundwater monitoring wells was stored in drums on
<br /> site, pending characterization and disposal
<br /> Groundwater Sampling Procedures
<br /> The groundwater monitoring wells were re-monitored to verify at least 80% recovery prior to
<br /> sampling Adequate recovery was observed in the purged wells prior to sampling A disposable
<br /> bailer was used to collect the groundwater samples All samples were collected in appropriate
<br /> containers, preserved on ice, and transported under chain-of-custody manifest to K1ff Analytical
<br /> LLC located in Davis, California
<br /> The water samples were analyzed for TPHg, BTEX, MtBE, TBA, DIPE, ETBE, TAME, 1,2-
<br /> DCA, and EDB using EPA method 8260B
<br /> Groundwater Analytical Results
<br /> Histoncal and recent groundwater laboratory analytical results are summanzed in Table 3 The
<br /> highest TPHg concentration was detected in monitoring well MW-3 at 24,000 parts per billion
<br /> (ppb) (Figure 4) The highest benzene concentration was detected in monitoring well MW-2 at
<br /> 1,500 ppb MtBE concentrations were highest in MW-2 at 100 ppb MW-6 and MW-9, wells
<br /> previously reported as non-detect,contained low levels of TPHg, BTEX, and MtBE The water
<br /> samples collected from domestic wells DW-1, DW-3, and DW-4 did not contain detectable
<br /> concentrations of TPHg, BTEX, or oxygenates, including MtBE Copies of the laboratory
<br /> analytical reports and chain-of-custody manifests are included in Attachment 4
<br /> Conclusion
<br /> Ten groundwater monitoring wells and three domestic water wells were sampled this quarter
<br /> Groundwater elevation raised an average 0 67 feet since August 2000 Refemng to Table 3, a
<br /> significant decline in the concentration of benzene, TPHg, and MtBE was observed in wells
<br /> MW-1, MW-2, MW-3, and MW-4 that are centered about the former tank pit Conversely, the
<br /> concentration of benzene, TPHg, and MtBE increased in three perimeter wells MW-6 located
<br /> upgradient of the former UST, MW-8 located cross gradient of the former UST, and MW-9
<br /> located downgradient of the former UST No concentrations of BTEX, TPHg, oxygenates, 1,2-
<br /> DCA, or EDB were detected above the laboratory reporting limits in the deep depth discrete well
<br /> File Riverbank-004Q
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