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i a <br /> e <br /> 620 West Charter Way <br /> Page 3 of 3 <br /> annually because of their down-gradient location from known source areas. In addition to <br /> CETI's proposed quarterly schedule for sampling MW-7, MW-8, and MW-,9, well MW-2 <br /> should continue to be sampled quarterly since groundwater samples collected from MW-2 <br /> demonstrate'the presence of COCs above or near the maximum contaminant levels (MCLS) <br /> established by the California Environmental Protection Agency Regional .Water Quality <br /> Control Board Central Valley Region for water quality goals. Continue collecting depth to <br /> water measurements in all wells during each quarterly groundwater monitoring event for <br /> the purpose. of determining the groundwater flow direction and gradient. EHD also <br /> recommends that 1,2-dichloroethane (1,2-DCA), 1,2-dibromroethane (EDB), ethanol, and <br /> methanol be, removed from the analytical list for all ten shallow monitoring wells since <br /> these compounds have not been detected in any of these wells. However, this does not <br /> apply to future wells proposed for monitoring the deeper zones. <br /> In addition to the monitoring well described above, EHD believes that two additional <br /> monitoring wells are needed to investigate the deeper zones. EHD recommends an <br /> intermediate depth monitoring well be installed near CPT-4 and CPT-5, screened between <br /> 45 and 50 feet bsg, and a deep well be:installed near CPT-10, screened between 67 and 72 <br /> feet bsg. Groundwater samples from jhese deep wells should be analyzed for benzene, <br /> toluene, ethyl benzene, and total xylenes (BTEX), TPH-g, MTBE, tertiary'butyl alcohol <br /> (TBA), ethyl tertiary butyl ether (ETBE), tertiary-amyl methyl ether (TAME), diisopropyl <br /> ether (DIPE), 1,2-DCA, and EDB. <br /> I <br /> Review of the quarterly groundwater monitoring data shows a significant increase of <br /> MTBE concentration in MW-8 since the May 2003 sampling event, approximately ten <br /> months after, CPT-5 was advanced in June 2002. Also high concentrations;of TBA have <br /> been reported in MW-8 and MW-9 'since November 2003. Therefore, in addition to j <br /> CETI's proposed CPT boring down gradient of MW-9, EHD directs you to investigate the <br /> vertical and lateral extent of MTBE and TBA contamination in soil and groundwater in the <br /> immediate vicinity of MW-8. This includes assessing the current operating underground <br /> storage tank system for leaks and taking corrective action, if appropriate. <br /> If you have any questions regarding this letter, please contact Vicki McCartney at (209) <br /> 468-3456 or:by electronic mail at vmccartneyLo)sjcehd.com. <br /> Donna Heran,REHS,Director <br /> Environmental Health Department <br /> O � <br /> Victoria L. McCartney, Senior RENS Nuel C. Henderson, Jr.,PG I <br /> Unit IV-Site Mitigation Unit IV- Site Mitigation <br /> i <br /> c: James L.L. Barton,PG— CVRWQCB <br /> Aubrey K. Cool,PG—CETI <br />