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Y ff enviros., May 1, 1996 - Ms. Mary Meays San Joaquin County Public Health Services Site Mitigation Unit P.O. Box 388 Stockton, California 95201-0388 RE: Work Plan Shell Service Station 6131 Pacific Avenue Stockton, California WIC#204-7525-0104 Dear Ms. Meays: Enviros, Inc. (Enviros) has prepared this work plan for Shell Oil Products Company (Shell) for the referenced site (Plate 1). This work plan responds to San Joaquin County Public Health Services (SJCPHS) correspondence dated December 13, 1995 and discussions from a meeting held between SJCPHS and Shell on February 2, 1996. The objectives of this work plan are: • to further delineate the extent of petroleum hydrocarbons in soil and ground water, and • to describe prior vapor extraction feasibility testing results. Site Description & Background The subject site is located on the southeast corner of the intersection of Pacific Avenue and Porter Avenue in Stockton, California(Figure 2). In 1990, the former underground fuel storage tanks (USTs) were removed. A total of fourteen soil borings (B-1 through B-14) were drilled and sampled. Total Petroleum Hydrocarbons calculated as Gasoline (TPH-G) concentrations ranged from ND to 17,000 parts per million (ppm) in selected soil samples. Benzene concentrations ranged from ND to 400 ppm. Borings TS-1 through TS-6 were drilled through the former UST complex to a depth of 16 feet below grade (fbg). Borings TR-1 through TR-6 were drilled along product lines and near dispenser islands. TPH-G concentrations were detected in soil samples ranging from ND to 19,000 ppm. Benzene concentrations were detected in soils ranging from ND to 280 ppm. Monitoring wells MW-1 through MW-3 were installed to evaluate ground water quality. Soils from these well borings contained TPH-G ranging from ND to 28 ppm and benzene ranging from ND to 0.38 ppm. Vapor extraction well VEW-2 soils contained TPH-G ranging from 2800 to 12,000 ppm and benzene ranging from 18 to 110 ppm. Soil analytical results are presented in Table 1 -Analytical Results: Soil. In late 1991 and early 1992, a 75-day vapor extraction feasibility test was performed at the subject site using wells VEW-1,VEW-2, and MW-3 (Figure 2). Wells VEW-1 and VEW-2 were tested to evaluate their feasibility in addressing petroleum hydrocarbons detected below the former USTs location. Well MW-3 was selected based on previously detected separate-phase hydrocarbons (SPHs) detected in this well. However, no SPHs have been detected in well MW-3 since August 1993. Enviros. Inc. 270 Perkins Street Sonoma, California To/707/935-4850 P.O. Box 259 95476-0259 Fax 7071935-6649