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f0/11/2002 13:06 707-585 "900 VERTEX ENG PAGE 06/13 PG&E provides electricity to the property. A distribution sub-station. is located soutb. of the Property beyond the adjacent vacant lot. Potable water is supplied by the City of Tracy municipal water system. The sewer system discharges to the City of Tracy municipal sewer system. Natural gas service is not currently provided to the site. All utilities enter the site on the west side of the property, A current United States Geological Survey (USGS) 7.5-minute topographic map depicting the location of the site was obtained and reviewed. The location of the site is shown on the 1981 USGS Tracy, California quadrangle map. According to the elevation contour lines on the topographic map, the site is located at an elevation. of approximately 40 feet above mean sea level (msl). Topography in the vicinity of the site slopes to the northwest. According to the USGS topographic map depicting the location of the site, the site is not within a,designated wetland. area. According to historical data, the site contained a bin storage area, a water tank, and pump house from approximately the 1960's through 1999. In, November 1999, Schack & Company, j. c. reportedly removed a 12-foot by 24-foot guard shack, 2 metal lean-to buildings, and the associated building foundations and walkways. Currently, the site consists of a vacant lot with no remaining building improvements. 3.0 GEOLOGY AND HYDROGEOLOGX Geologic information obtained from previous reports indicates that the surface geology in the vicinity of the site consists of fine-grained silts and clays down to 20 to 25 feet below ground surface (bgs). Underlying the first layer is a gravelly clay layer 5 to 8 feet thick, which is underlain by a sand/silty sand water-bearing Iayer. The groundwater, table is reported to be at a depth of 10 to 12 feet bgs and varies with seasonal changes. The groundwater flow direction has been documented to be north-northeast. 4.0 FIELD INVESTIGATION The purpose of this supplemental site assessment is to investigate for the potential presence of VOCs in groundwater along the (hydraulically up-gradient) western. property boundary at the subject site. To investigate groundwater conditions hi this area, VERTEX will install four temporary groundwater monitoring wells at selected locations. Groundwater, samples will be collected from these temporary wells. Following collection of groundwater samples, the temporary well casing will be removed and borings will be backfilled with cement grout according to San Joaquin County requirements. A site specific Health &Safety Plan has been prepared and attached as Appendix A. VERTEX field staff and subcontractors will review the plan prior to conducting work at the site, The following sections present the methods and procedures that will be used for this investigation. 2