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this group (Figure 2). The Modesto Formation of Late Pleistocene is the youngest and occurs at the surface in the Stockton area. This formation is approximately 100 feet thick here but thickens westward toward the axis of the San Joaquin Valley (The geological data were obtained from the San Jose Sheet - Geological Map of California, 1966, California Divisions of Mines and Geology and from United States Geological Survey Open-File Report 77-748, 1977). The site lies within the limits of San Joaquin Valley Water Basin (Basin No. 5-22) of the San Joaquin Basin Hydrologic Study Area, which is drained primarily by the San Joaquin River. Two aquifers are recognized to exist at the site; a deep and a shallow aquifer. The deeper aquifer contains connate water occurring in the semi-consolidated to consolidated Merhten and Valley Spring Formations. The fresh water bearing formation, consisting of alluvial sediments occurs in a shallower depth. These two aquifers are hydraulically separated from each other. 2.4 Depth to Groundwater Groundwater was estimated at approximately 80 feet below surface grade by San Joaquin County Department of Public Works, Flood Control Section (Spring 1993). 3.0 ASSESSMENT PROCEDURES Prior to performing any work at the site, a Site Assessment Work Plan (dated February 1994) detailing the objectives and procedures of the limited site assessment, was prepared by GeoAudit and submitted to the San Joaquin County Public Health Services - a Environmental Health Division (PHS/EHD). The procedures for completing the workplan objectives are presented in the following sections. 3.1 Drilling and Sampling A preliminary assessment was performed by GeoAudit on March 2, 1994. Four soil borings (Bl through B4) were drilled and sampled near the location of the former UST. Boring B1 was continuous and located in the center of the former gasoline tank cavity. Boring B1 was terminated at 38 feet below ground surface (bgs). Boring B4 was located approximately 10 feet west of the former tank cavity and was terminated vertically at 60 feet bgs. Boring B4 was drilled to 60 feet bgs in an attempt to document the depth to groundwater on site. The boring was terminated before groundwater was encountered. Borings B2 and B3, located north and south of the former tank cavity, were terminated at 30 feet bgs. The boring locations are illustrated on Figure 3. All borings were backfilled with Portland Cement to the surface. Auger returns were stored on plastic sheeting within the fenced area located to the south of the work bays. Upon the completion of drilling activities, the soil was covered and secured with plastic sheeting. All borings were drilled using a truck-mounted Mobile B-53 drill rig. The drill rig and two- C—bginl Audit Service,Inc. 3 M-s��R Rpt/D..'.au�.