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EVAX Project B239-02 April 7, 1992 r� , s D� INTRODUCTION 1 EVAX Technologies, Inc. (EVAX) was retained by Messrs. Jack Vaughn and Darryl Christensen to install and sample 3 groundwater monitoring wells at 595 East 11th Street in Tracy, San Joaquin County, California. The attached Site Vicinity Map, Figure 1, shows the location of the property. The property is owned by Messrs. Vaughn and Christensen, and currently encompasses a muffler repair shop (Ed's Muffler Shop), 1 welding shop, and residential trailer park. The main purpose of the investigation was to evaluate if groundwater at the site was impacted by gasoline hydrocarbon products. SITE BACKGROUND 1 Tank Removal (January 1990) In January 1990, 4 underground storage tanks (USTs) were excavated and removed from the site at Ed's Muffler Shop. The tank complex consisted of an 8,000-gallon capacity tank used to store regular leaded gasoline, 7,500-gallon capacity tank used to store regular unleaded gasoline, and ' !� two 4,000-gallon capacity tanks each used for premium unleaded gasoline. A waste oil UST was reportedly also removed at the time. The attached Site Map, Figure 2, presents the location of the former USTs and service islands. During the tank removal operation, soils were sampled from beneath each end of each tank and from beneath piping at the service islands. In addition, a sample was taken of the water which accumulated in the fuel USTs pit. The water and 13 soil samples were submitted to FGL Environmental of Stockton, California and analyzed for petroleum hydrocarbon product constituents. Laboratory analyses results, summarized in the attached Table 1, indicated soils around the former i USTs were impacted by petroleum hydrocarbon products. Soil Gas Survey (January 1992) 4n January 1992, EVAX conducted a soil gas survey to test soils for volatile hydrocarbon concentrations. A total of 17 temporary vapor extraction probes were each installed to a depth of approximately 11 feet below ground surface. Soil gases were extracted by vacuum from each probe and analyzed for total volatile hydrocarbon/organic content by a portable flame ionization detector (FID) . Results of the soil gas survey indicated TVH concentrations of up to 32,000 part per million (ppm) near and north of the USTs. Results of the soil gas survey were Presented in EVAX Report B239-01, dated January 8, 1992.