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r 21 01 Webster Street <br /> 12th Floor <br /> Oakland, CA 94612 <br /> [51 O) 663-41 00 e FAX (B 1 O) 663-4141 GEOMATRIX <br /> August 24, 2000 <br /> Project 6447 <br /> Mr. Robert D. Mihalovich <br /> Chevron Environmental Management Company <br /> P.O. Box 6012 <br /> San Ramon, California 94583-0712 <br /> Subject: Response to RWQCB Comments . <br /> Former Mansfield Property <br /> Tracy, California <br /> Dear Mr. Mihalovich: <br /> Geomatrix Consultants, Inc. (Geomatrix) has prepared this letter responding to the California <br /> Regional Water Quality Control Board, Central Valley Region's (RWQCB) comments to the <br /> Geomatrix work plan "Grab Groundwater Sampling Work Plan, Former Mansfield Property, <br /> Byron.Road, Tracy, California"dated June 29, 2000. In their August 3, 2000 letter to CEMC, <br /> the RWQCB conditionally approved the work plan. The RWQCB's comment regarding the <br /> work plan is presented below in italics, followed by our response. <br /> My 14 March letter requested resampling of locations BS, B6, B7, B9, and B12 for TPHd <br /> analysis without silica gel cleanup. The workplan proposes resampling B5, B7, and B9 only, <br /> but does not provide the rationale for elimination of B6 and B12. These locations need to be <br /> included in the sampling program to provide sufficient coverage of the area downgradient of <br /> TPH-affected soil. The workplan is conditionally approved provided that B6 and B12 are <br /> included in the sampling program. <br /> Geomatrix originally proposed collecting grab groundwater samples at three locations (135, <br /> B7, and B9)because we believe that these locations provide sufficient coverage to <br /> characterize groundwater quality immediately downgradient of affected soil. However, to <br /> address RWQCB's request, a fourth location will be added near former boring B 12. Because <br /> former borings B5 and B6 are in close proximity, a single boring between the locations of the <br /> two former borings is sufficient to assess groundwater quality in this area. <br /> In summary, Geomatrix plans to collect grab groundwater samples at or adjacent to the <br /> locations of former borings B7, B9, and B 12 and a fourth boring located halfway between <br /> former borings B5 and B6 (Figure 1). Samples will be collected and analyzed as described in <br /> the June 29, 2000 work plan. <br /> I <br /> Geomatrix Consultants, Inc. <br /> Engineers, Geologists, and Environmental Scientists <br />