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MEMORANDUM <br /> CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARD - CENTRAL VALLEY REGION <br /> 3443 Routier Road Phone: (916) 361-5600 <br /> Sacramento, CA 95827-3098 ATSS Phone: 8-495-5600 <br /> TO: Antonia K.J. Vorster FROM: John J. Tomko <br /> i <br /> D �r� <br /> DATE. 22 November 1989 SIGNATURE. <br /> SUBJECT: TRACY ORCHARD PROJECT, CHEVRON PIPELINE LEAK, TRACY, SAN JOAQUIN COUNTY <br /> I have reviewed a work plan, received on 23 October 1989, for additional subsurface <br /> investigation at the Chevron pipeline fuel spill. site (Tracy Orchard, Inc.) in Tracy. The <br /> subsurface investigation is currently being conducted by Western Geologic Resources (WGR) . <br /> Dames and Moore, in 1987, supervised the removal of approximately 100 cubic yards of <br /> contaminated soil from the site, and the installation of three monitoring wells. These <br /> monitoring wells are approximately 20 feet deep with 15-foot well screens. Ground water <br /> flow direction, based upon water level readings, was determined to be towards the northeast. <br /> Water samples from these monitoring wells did not have detectable levels of benzene, toluene, <br /> or xylene. Plate 8 (attached) shows the location of the spill area, the dewatering wells, <br /> the monitoring wells, and the ground water table contours for 6 June 1987. Lithologic logs <br /> for the three monitoring wells were developed and they indicate that the upper water bearing <br /> zone appears to be a sandy layer from four to eight feet thick and at a depth below the <br /> ground surface from 10 to 17 feet. Water samples were taken by Regional Board staff in 1987 <br /> from the three dewatering wells. Dewatering well DW-1 contained benzene at 510 ppb, toluene <br /> at 903 ppb, and ethyl benzene at 226 ppb. <br /> WGR submitted a work plan on 28 April 1989 to conduct a soil vapor survey in the area of the <br /> spill . The work plan was approved by Regional Board staff. A summary of the results of <br /> this survey, and the resampling of the dewatering wells (DW), the monitoring wells (MW) , <br /> and two domestic water supply wells (SW), were contained in the work plan received this <br /> October. The analytical results of the well sampling effort were. summarized in the report <br /> and are shown in the table on the following page (see Figure 2 for well locations) . <br /> Twenty-two soil vapor samples were taken. A total volatile hydrocarbon (TVH) level of 210 <br /> ppm was detected near the west end of the spill area. TVH levels of 9.4 and 11.0 ppm were <br /> detected approximately 65 feet south of the spill area. <br /> The additional field work proposed by WGR includes: <br /> 1) Taking soil samples in a borehole for lithologic characterization. If PID <br /> readings of the samples are significant, analytical tests will be conducted. <br /> 2) Installing a four-inch diameter monitoring well within the borehole. This well <br /> will be located downgradient of the eastern edge of the spill area (Figure 2) . <br /> This well will extend 20 feet into the upper water bearing zone. <br /> 1 <br />