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4 L 2101 Webster Street <br /> 12th Floor <br /> U Oakland, CA 94612 <br /> (510) 663-4100 - FAX (510) 663-4141 GEOMATRIX <br /> June 29, 2000 <br /> Project 6447.004 <br /> I <br /> Mr. Robert Mihalovich <br /> i <br /> Chevron Environmental Management Company <br /> P.O. Box 6012 <br /> San Ramon, California 94583 <br /> Subject: Grab Groundwater Sampling Work Plan <br /> Former Mansfield Property <br /> Byron Road <br /> Tracy, California - <br /> Dear Mr. Mihalovich: <br /> i <br /> Geomatrix Consultants, Inc. (Geomatrix)has prepared this work plan for work to be <br /> conducted at the Mansfield Property(the site;Figure 1) on behalf of Chevron Environmental <br /> Management Company(CEMC). The proposed scope of work involves advancing three <br /> borings downgradient of the petroleum hydrocarbon-affected soil to collect grab groundwater <br /> samples as requested by California Regional Water Quality Control Board, Central Valley <br /> Region (RWQCB) in its March 14,'2000 letter and as described in CEMC's April 17, 2000 <br /> response letter. <br /> The objective of this investigation is to re-sample groundwater near previous downgradient <br /> grab groundwater sampling locations and analyze the samples for total petroleum <br /> hydrocarbons (TPH) quantified as diesel (TPHd). Previous grab groundwater samples were <br /> analyzed for TPHd following a silica gel preparation procedure which removes polar <br /> biodegradation byproducts from the sample extract. RWQCB has requested that additional <br /> samples by collected and analyzed for TPHd without silica gel preparation. It should be noted <br /> that all previous grab groundwater samples collected approximately 25 to 50 feet <br /> downgradient of affected soil (B-5, B-6, B-7, B-9, and B-12; Figure)were non-detect for <br /> benzene, toluene, ethylbenzene, xylenes, polynuclear aromatic hydrocarbons, TPH quantified <br /> as gasoline (TPHg), and TPHd following silica gel preparation. The proposed scope of <br /> additional work is described below. <br /> I <br /> Geomatrix will contract with Precision Sampling, Inc., of Richmond, California, to advance <br /> three soil borings and collect grab groundwater samples in the vicinity of previous borings <br /> B-5, B-7, and B-9' (Figure 2). During previous investigations at the site, groundwater was <br /> encountered at 10 to 11 feet below ground surface(bgs). Geomatrix will contract a private <br /> Geomatrix Consultants,Inc., 1999, Soil and Groundwater Investigation and Site Status Report,Mansfield <br /> Property(APN 209-270-30),Tracy California,June. <br /> Geomatrix Consultants, Inc. <br /> Engineers, Geologists, and Environmental Scientists <br />