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MW-5 (184 ppb gasoline, 7 8 ppb benzene, 1 0 ppb toluene, 1 0 ppb ethylbenzene, and 2 8 ppb xylenes), <br /> MW-7 ( 64 ppb gasoline, 1 9 ppb toluene, 0 7 ppb ethylbenzene, and 2 7 ppb xylenes, MW-8 (97 ppb <br /> gasoline and 4 5 ppb benzene, and 0 7 ppb xylenes), and MW-10 (256 ppb gasoline, 3 6 ppb benzene, <br /> 2 8 ppb toluene, 0 8 ppb ethylbenzene, and 3 6 ppb xylenes) Per the County's request, samples <br /> collected from MW-1 and MW-10 were analyzed for the presence of MTBE by EPA Method 8020 <br /> Analyses identified 7 9 ppb MTBE in the groundwater sample collected from MW-10, however, MTBE <br /> was not detected in the sample collected from MWA Table 2 in the attached report summarizes <br /> groundwater analytical data and laboratory reports are Included as Appendix B <br /> Conclusions <br /> Although the extent of groundwater Impacts Is not truly defined, the highest concentrations of <br /> hydrocarbons appear to remain onsite In the vicinity of the pump Islands (MW-1, MW-3 and MW-9) <br /> When compared to the December 1996 sampling event, groundwater concentrations Increased slightly In <br /> MW-6, MW-7, and MW-10, while slight decreases in hydrocarbon concentrations were observed in MW- <br /> 1, MW-3, MW-4, MW-5, and MW-9 Hydrocarbon concentrations In MW-2 and MW-8 remained <br /> relatively unchanged With the exclusion of MW-10, which contained hydrocarbons for the first time <br /> since monitoring began, the range of hydrocarbons observed is consistent with previously collected data <br /> Changes In hydrocarbon concentrations may be a result of a changes In groundwater elevation, however, <br /> not enough data has been collected to evaluate their significance Additional monitoring data will be <br /> collected to further evaluate the extent of the dissolved hydrocarbon plume <br /> Future Site Activities <br /> At this time, SECOR Is preparing a workplan for the completion of a feasibly study to evaluate <br /> appropriate remediation technologies for addressing Impacted soils and groundwater at the subject site <br /> Upon completion, the workplan will be forwarded for your review and comment Time will continue <br /> groundwater monitoring to further evaluate the plume of dissolved hydrocarbons beneath the subject <br /> site <br /> If you have any questions regarding these matters, please do not hesitate to contact me at (206) 286- <br /> 4495 <br /> Sincerely, <br /> Time Oil Co <br /> Anastasia E Duarte-Wilkinson <br /> Environmental Toxicologist <br /> cc Ms Elizabeth Thayer <br /> California Regional Water Quality Control Board <br /> aPrDA4049125 doc <br /> 2 <br />