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1 <br /> 6ETTLER - RYAN1 c N . � <br /> August 1, 2000 <br /> Mr Bob Boust <br /> Unocal- DBG/AMG ' <br /> CIO <br /> 8788 Elk Grove Boulevard <br /> Building 3, Suite 15 1 �� <br /> Elk Grove, CA 95624 s - , <br /> �YsyM <br /> Subject Review of Quarterly Monitoring Data from Foi mer Unocal Service Station #0123, 1034ntral <br /> 4 r <br /> Avenue,Tracy, CA <br /> Mr Boust <br /> I have reviewed the data from the second quarter 2000 monitoring and sampling event for the subject site Groundwater <br /> levels dropped an average of 51 feet from levels measured during the fitst quarter 2000 These levels are within the <br /> historical fluctuation range Duiing the second quarter 2000 groundk4ater flow was toward the north-northwest at a <br /> gradient of 005 These groundwater data ate consistent with the historical record <br /> Low concentrations of benzene and Total Petroleum I lydrocarbons as gasoline(TPHg)continue to be detected in on-site <br /> monitoring well U-4, situated in the source area However, these concentrations ate vety low Total Petroleum <br /> Hydrocarbons as dILSCI (TPHd) were detected only in well MW-2 at the laboratory teporting limit MtBE was not <br /> detected in any of the monitoring wells this quarter Hydrocarbons were not detected in downgradtent well MW-6 <br /> Hydi ocarbon concentrations and distribution detected during,the second quarter 2000 are consistent with historical data <br /> The dissolved plume is defined to the north (well MW-6, downgradient of the site) Lateral delineation of benzene has <br /> also been achieved(wells MW-1 and MW-2) The detectable concentrations of TPHg and TPHd at this site ate not high <br /> enough to warrant additional investigation Since this station ceased operation in the early 1960s,the historical presence <br /> of MtBE suggests at least some of the dissolved hydi ocarbons detected in the gt oundwater beneath the site is due to an <br /> off-site source Based on these data and conclusions, additional work at the site is not wai ranted The site appears to <br /> be of low risk, and should be considered for closure <br /> Please call us at 916 631 1300 if you have qu ` TG.R�4 GEO(O " <br /> Sincerely, <br /> Gctticr-Ryan Inc 9 <br /> Na 5577 � <br /> Steplicn J Carter tP \Q. <br /> Senior Geologist <br /> R G 5577 F0F CAL�F� <br /> Attachment Second Qum ler 2000 Groundwater Monitoring Sampling Rena t, G-R Job #280047 <br /> dated July 24,2000 <br /> cc Mr Mike Infurna, San Joaquin County Department of Environmental Health <br /> cc(without attachments) <br /> Kimberly Ayers and Leesa Ward, Ayers& Ward Real Estate investment Services, 1034 Central Avenue,Tracy, <br /> CA 95376 <br /> 6747 Sierra Court , Suite J Dublin , California 94568 ( 925 ) 551 - 7555 <br />