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i Wright Environmental ` May 31, 1996 Services, Inc. j Project No. 4070-T M&M Automotive 60 East Tenth Street t Tracy, CA 95376 i Attn: Mr. Larry McLean i Re: Proposed Source Removal Cleanup and Monitoring Workplan, M &M Automotive, 60 E. 10th Street, Tracy, CA 95376 Dear Mr. McLean, , An underground gasoline storage tank was removed from the:M & M Automotive site in November, 1991 where contamination was observed in 'the tank .pit. Three groundwater monitoring wells exist on-site and some plume definition has been performed by Wright EnvironmentalServices, Inc. (Wright) in a. preliminary environmental assessment report dated March 10, 1995. Since some soil contamination was found to remain in the area of the .tank pit, dispenser island (collectively the source), and had been mapped into 10th Street, additional subsurface investigation to define the horizontal and vertical extent of soil and groundwater contamination was required by San Joaquin County Public Health Services, Environmental Health Division (PHS-EHD). Wright completed the soil and groundwater plume definition which was presented in the Problem Assessment Report (PAR) dated April 29, 1996. Based upon analysis of data gathered during the preliminary environmental assessment and the subsequent assessment work in March 1996 and April 1996 respectively, Wright has found the migration of contaminants on the capillary fringe away from the source has caused the groundwater problem, typical of sites with petroleum fuel contaminants. Seasonal groundwater fluctuations and infiltration from storm events may cause some additional spreading of contaminates, however, over time the plume has migrated only -a short distance under 10th Street, just north of the site. Introduction and Technical Approach Discussions with the PHS-EHD representative indicates concurrence with Wright that the groundwater plume has been defined by the work presented in the PAR, and plume movement is limited in extent. In addition a limited vadose soil cleanup of the former tank excavation and pump island area (the source) is warranted at this time. This would remove contaminants in the vicinity of the former tank and pump island which appear to be a continuing source of groundwater contamination. This is a consistent. approach with the current and evolving guidance prepared by the California Regional Water Quality Control Board, Central Valley Region (RWQCB) and the State Water Resources Control Board (SWRCB). Wright understands that the RWQCB and SWRCB guidance and policy issues currently under review may be modified in the future however, site definition source removal and monitoring of wells around the groundwater plume appear to be the limits to which these modifications will go. ' 4220 Commercial Dr.#5 • Tracy, California 95376 Telephone (209) 833-0758 • Fax (209) 832-5152