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3164 Gold Camp Drive Delta Suite 200 /�. Rancho Cardona CA 95670 Enviranmental 916/638 2085 Consultants,Inc FAX 9161638-8385 August 20, 1997 Ms Marla D Guensler Exxon Company, U S A 2300 Clayton Road, Suite 640 Concord, California 94520 Subject Pilot Testing Results and Proposed Remedial Action Plan Former Exxon Service Station No 7-3708 2705 Country Club Boulevard Stockton, California Delta Project No D093-809 Dear Ms Guensler Delta Environmental Consultants, Inc (Delta), has been authorized by Exxon Company, U S A (Exxon), to install one sod vapor extraction (SVE) well, conduct a pilot test, and propose a remedial action plan for Exxon Service Station No 7-3708 located at 2705 Country Club Boulevard, Stockton, San Joaquin County, California (Figure 1) This report describes the work performed in accordance with Delta's Proposed Additional Hydrogeologic Investigative Work (work plan), dated February 27, 1997, as approved by the San Joaquin County Environmental Health Division (SJCEHD) A copy of the SJCEHD approval to the work plan, SVE well permit, and San Joaquin Valley Unified Air Pollution Control District approval letter, are included in Enclosure A Proiect Background Information In August 1991, Delta installed three on-site ground water monitoring wells (MW-1 through MW-3) to evaluate the extent of petroleum hydrocarbons in soil and ground water beneath the site Three additional wells (MW-4 through MW-6) were installed off-site (downgradient) in February 1992 In March 1994, two additional ground water monitoring wells (MW-7 and MW-8) were installed to assess the up and cross-gradient extent of dissolved petroleum hydrocarbons in ground water The location of the monitoring wells are shown in Figure 2 The soil types encountered consist of sands, silts, and clays in variable compositions Analytical results for collected soil samples are summarized in Table 1 The ground water table has been present at approximately 6 to 17 feet below surface grade (bsg) with observed seasonal fluctuations (Table 2) The direction of ground water flow beneath the site has consistently been toward the northeast with a gradient of less than 0 01 (Figure 3) Quarterly ground water sampling has been conducted at the site since August 1991 Since the last four quarters, benzene, toluene, ethylbenzene, and total xylenes, (BTEX) have ranged from below the laboratory analytical method detection limit of 0 5 micrograms per liter (1tg/L) in several wells to 580 Etg/L in the ground water sample collected from monitonng well MW-3, in July 1996 (Table 2) Petroleum hydrocarbon constituents in ground water samples collected from monitoring wells MW-1, Providing a Competitive Edge