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May 6, 1992 Former Unocal Station 2859, Stockton, California monitoring wells were installed offsite to delineate dissolved hydrocarbons (Applied GeoSystems, December 12, 1990, Report No 38012-5) The locations of the wells are shown on Plate 2 In response to the detection of hydrocarbons in soil and ground water, RESNA began periodic monitoring of the ground water in June 1988 Results of previous monitoring events indicated that dissolved hydrocarbons were detected in water samples collected from the five wells, the highest concentrations of hydrocarbons were detected in well MW-2 We evaluated the direction of ground-water flow to be northeast from June 1988 to May 1990 Wells MW-1, MW-2 and MW-3 have been dry since the July 1990, therefore these wells were not sampled and the direction of ground-water flow was not be evaluated MONITORING AND VAPOR-EXTRACTION WELL INSTALLATION The drilling operations, soil sampling, and well construction and development are summarized below Our field methods and Chain of Custody protocol are described in an attachment to this report Copies of the Chain of Custody records and laboratory reports for soil and water samples are attached Work was conducted according to field methods outlined in our Work Plan No 38012-6W, dated July 10, 1991 •� Drilling, Soil Sampling, and Well Construction During the week of February 24, 1992, a geologist from RESNA observed Wayne Drilling of Lincoln, California, drill five 8-inch-diameter soil borings (13-7 through B-11), boring B-7 was drilled offsite and borings B-8 through B-11 were drilled onsite (Plate 2). Soil samples • were collected at approximately 5-foot intervals during drilling and were identified using visual and manual methods and classified according to the Unified Soil Classification System (Plate 3) Ground water was encountered at approximately 52 to 53 feet below grade Descriptions of the materials encountered are presented in the Logs of Borings (Plates 4 through 16) • Wayne Drilling installed ground-water monitoring wells MW-6 and MW-7 in borings B-7 and B-8, respectively, and vapor-extraction wells VW-1, VW-2, and VW-3 in borings B-9, B-10, and B-11, respectively Well construction details are illustrated on the Logs of Barings A technician from RESNA was onsite February 28, 1992, to develop wells MW-6 • and MW-7 Further details of the geology at the site will be discussed in the Problem Assessment Report Four soil samples were collected from the drill cuttings and composited into one sample in the laboratory for analyses Results of the composite soil sample were used to evaluate disposal options of the drill cuttings At Unocal's request, drill cuttings were removed and disposed of by Dillard Trucking of Byron, California • 0317bbou 38012-9 2