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Ms. Kay Huffman 28 March 1988 3 WEISSASSOCL4TEs 1 8. Report the results. These tasks are briefly described below. BACKCROUND Three inalled at the site byoGroundwatermTechnologyonitoring winlOctobers, MW-1�1986MW-2�(Figure and -32). Thestwell. were installed to identify the impact of a product line leak near the outer pump island. Monitoring wells MW-1 and MW-3 are 32 ft deep and MW-2 is 36 EL deep. The wells were constructed with 2-inch-diametor PVC well screen and blank casing. Ground water was et,countered at approximately 24 ft below grade In MW-1 and MW-3 and at 32 ft below grade in MW-2. The screened intervals in MW-1, and MW-3 extend from 10 Et to 32 ft below grade and in MW-2 from 6 ft to 36 ft below grade. The monitoring wells were screened across unsaturated soil intervals with hydrocarbon odors. Ground water samples from the three wells contained between 0.16 and 76 parts per million (ppm) benzene, 0.17 and 60 ppm toluene and 0.004 and 0.15 ppm xylenes in October 1986. The monitoring wells were resampled in March 1987 and contained between 1.26 and 697 ppm benzene and <1,0 and 137 ppm toluene, but the samples were not analyzed for xylenes. Monitoring well MW-2, the well closest to the buried tanks, had the highest concentrations of benzene and toluene. —,. On 12 December 1987, EA Engineering Science and Technology, Inc. (EA) conducted a soil vapor contaminant assessment at the site. Soil gas samples 1 we::e taken from depths between 3 and 10 ft below grade. The highest concentrations of hydrocarbons in soil vapor were detected south and east of the pump islands, The highest hydrocarbon concentrations were detected in the headspace of the monitoring wells. Weiss Associates was retained by Chevron to drill borings and install additional ground water monitoring wells at the site. The borings were located to provide preliminary definition of the vertical and lateral extent of hydrocarbons beneath the site. SUPPLY WELL INVENTORY An inventory of wells within a 1/2-mile radius of the property was obtained from the Department of Water Resources in Sacramento and from the EA report (Figure 3), Well numbers, owners, addresses, locations, date o drilling and use are shown in Table 1, f SOIL BORING AND MONITORING WELL INSTALLATION On 19, 20, 21, and 22 January 1988, borings 34 through B7 were drilled, under the supervision of WA geologist Sharon Halper, by Westek of Sun lose, California, using a mobile CME-55 hollow-stem drill rig (Figure 2). ;oil l samples were collected in new, steam-cleaned, 2-inch-diameter brass :ubes. Soil samples were removed from the sampler, trimmed, capped with aluminum foil and plastic caps, hermetically sealed with duct tape and refrigerated during