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Webster Street <br /> 12th <br /> 12th Floor <br /> Oakland, CA 54692 <br /> C51 0) 663-4'100 • FAX (590) 663-4149 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 Lyoth Loading Station <br /> Tracy, California <br /> Dear Mr. Mihalovich: <br /> Geomatrix Consultants, Inc. (Geomatrix) has prepared this letter responding to 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 Lyoth Loading <br /> Station, 26501 Banta Road, Tracy, California" dated June 29, 2000. In their August 3, 2000 <br /> letter to CEMC, the RWQCB conditionally approved the work plan. The RWQCB's <br /> comment regarding the former Lyoth Loading Station is presented below in italics, followed <br /> by our response. <br /> My 14 March letter requested definition of the lateral extent of the TPHd plumes at MWs 6 <br /> and 7 via installation of a MW downgradient of MWs 6 and 7. The workplan proposes to <br /> install a boring/temporary well downgradient of MW--7, collect groundwater samples, and <br /> grout the boring after sample collection. The workplan is inadequate because it does not <br /> propose a permanent MW downgradient of MW-7. In addition, it does not have provisions to <br /> define the lateral extent of the TPHd plume at MW-6. The workplan is conditionally <br /> approved provided that Chevron installs a MW downgradient of MW--7 and defines the plume <br /> at MW-6. <br /> To date MW-7 has been monitored a total of eight times between April 1997 and July 2000. <br /> The only compounds detected in MW-7 (with the exception of pyrene detected one time at the <br /> detection limit of 0.1 micrograms per liter [µg/1])have been biogenic byproducts resulting <br /> from natural degradation of the crude oil. These compounds are detected in the analyses for <br /> total petroleum hydrocarbons quantified as diesel (TPHd) when analyzed without a silica gel <br /> preparation procedure. The RWQCB has requested that CEMC install a monitoring well to <br /> assess the extent of these biodegradation byproducts (quantified as TPHd) downgradient of <br /> MW-7 and assess the extent of biodegradation byproducts downgradient of MW-6. <br /> To address RWQCB's request, Geomatrix will add a grab groundwater sampling location <br /> downgradient of MW-6 (Figure 1). However, Geomatrix continues to propose collection of <br /> grab groundwater samples downgradient of MW-6 and MW-7 rather than installation of <br /> permanent monitoring wells because the grab groundwater samples will sufficiently <br /> Geomatrix Consultants, Inc. <br /> Engineers, Geologists, and Environmental Scientists <br />