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2101 Webster Street <br /> 12th Floor <br /> Oakland, CA 94612 <br /> (510) 663-4100 • FAX (510) 663-4141 GEOMATRIX <br /> August 13, 1999 <br /> Project 5223 <br /> Ms. Kristen Rocha <br /> Regional Water QualityControl Board 41JG1 �® <br /> Central Valley Region ENVIR0/ 61999 <br /> 3443 Sacramento,rCal Califore A nia 827-3098 PERNj;ME�rAL HEAT <br /> RVjCEs H <br /> Subject: Schedule and Plan for Additional Sampling <br /> Mansfield Property <br /> Tracy, California <br /> Dear Ms. Rocha: <br /> Geomatrix Consultants, Inc. (Geomatrix), on behalf of Chevron Environmental Management <br /> Company(Chevron), plans to advance one additional boring at the Mansfield Property site <br /> (Figure 1) to collect additional soil and grab groundwater samples. The proposal to perform <br /> this additional work was approved by the California Regional Water Quality Control Board, <br /> Central Valley Region(RWQCB) in your July 30, 1999 letter. The soil and grab groundwater <br /> samples will be used to assess the potential presence of dissolved-phase petroleum <br /> hydrocarbon constituents in groundwater downgradient from a previously delineated area of <br /> petroleum hydrocarbon affected soil; these data will finalize the site assessment for the <br /> property. <br /> Prior to the commencement of field activities, Geomatrix will obtain a boring permit from San <br /> Joaquin County Public Health Services (SJCPHS) and will contact Underground Service Alert <br /> (USA). Geomatrix proposes advancing the boring in the vicinity of boring B-14, <br /> downgradient from boring MB-1 (Figure 2). The boring will be advanced to approximately 13 <br /> feet below ground surface using a hydraulically-driven direct push core barrel and drive <br /> sampler. Soil recovered from the continuous core will be examined and logged in accordance <br /> with the Unified Soil Classification System (USCS) as presented in the American Society of <br /> Testing and Materials Standard D2488-90. One soil sample will be collected for chemical <br /> analysis from directly above the saturated zone for chemical analyses. The soil sample will be <br /> collected in a stainless steel liner, sealed with Teflon sheets,plastic end caps, and tape, <br /> labeled, and stored in an ice-cooled chest. <br /> Once the presence of groundwater is confirmed in the borehole, temporary one-inch diameter <br /> polyvinyl chloride(PVC) blank casing and well screen will be installed and a groundwater <br /> sample will be collected. The groundwater sample will be collected using a disposable bailer <br /> and will be decanted into 40-m1 volatile organic analysis (VOA) vials and 1-liter amber <br /> bottles. Sample containers will be labeled, sealed in plastic bags, and stored in an ice-cooled <br /> Geomatrix Consultants, Inc. <br /> Engineers. Geologists, and Environmental Scientists <br />