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u i 3 r SITE GEOLOGY Quartenary alluvial deposits immediately underlie the Tracy area. These deposits, which may be up to 350 feet thick, are made up of interbedded clay, silt, sand, and gravel. According to the underground utility maps provided by the City of Tracy (see Figure 2), one well exists approximately 1,200 feet southwest of the subject site. This is probably a municipal well and is the only well in the area indicated on the map. FIELD METHODS F { This section describes the field methods for this investigation. Borehole Drilling and Soil Sampling I Brown and Caldwell (BC) will supervise the drilling of six boreholes (see Figure 3) and the installation of groundwater monitoring wells in three of the boreholes at the site. The boreholes will be drilled using a truck-mounted drilling rig equipped with 8-inch- outside-diameter by flinch' -in.side-diameter hollow-stem augers. All drill cuttings from the boreholes will be containerized on site in 55-gallon drums. Diamond Properties will be responsible for disposal of the drill cuttings. y. The depth to groundwater is approximately 11 feet. Borehole depth is not expected to be deeper than 30 feet. During drilling, two soil samples will be collected from each of the three deeper FI boreholes. One soil sample each will be collected from the boreholes near the former <r locations of the underground gasoline storage tank, waste oil tank, and pump island areas. Samples will be obtained using a 2-inch-inside-diameter by 18-inch-long, split-spoon sampler driven into undisturbed soil with a 140-pound hammer dropped 30 inches. When the drive sampler is removed from the borehole, the soil will 'be visually inspected in the field to identify lithology. The samples will be submitted to the laboratory to be analyzed for total petroleum fuel hydrocarbons using U.S. Environmental Protection Agency (EPA) Method 8015, modified, benzene, toluene, and xylene (BTX) using EPA Method 8020, and tetra ethyl lead using the California Department of Health Services (DHS) method for organic lead. Installation or Groundwater Monitoring Wells This section describes the methods for monitoring well construction, development, and sampling. Groundwater Monitoring Wells. Construction of wells will be completed with 2- inch-diameter, polyvinyl chloride (PVC), flush-threaded casing and will be screened with 0.020-inch slotted casing from 10 feet below the groundwater surface to 5 feet above the