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1 r extraction wells will be proposed and installed to complete remediation of the ' site 2 Depending on the efficiency of reinjection of water into existing wells, addi- tional infection wells may be proposed and installed 3. Borings will be drilled and sampled, and samples will be chemically ana- lyzed for petroleum hydrocarbons to confirm that petroleum hydrocarbons have been removed from the soils ' The full scope of the work plan is described in the following text 1.1 SETTING The site, located at 4444 Pershing Avenue in the northwest part of Stockton, is near the north ' bank of the Calaveras River, about 2.5 miles from its confluence with the San Joaquin River (Figure 1). According to maps of the San Joaquin County Flood Control and Water Conserva- tion District (FCWCD), the groundwater gradient near the site is to the northeast, parallel to the Calaveras River, but groundwater pumping in the city forces flow in the upstream direction At present, the site, on the southeast corner of North Pershing Avenue and Rosemarie Lane, is an unimproved grassy lot from which all buildings and installations have been removed. The areas to the northeast and southwest of the site are occupied by apartment buildings (Figure 2). Across I Pershing Avenue and Rosemarie Lane, about 100-200 feet from the site boundaries, there are Shell and 7-Eleven service stations and office buildings. North of the site, across Rosemarie Lane, is the Chateau Convalescent Hospital Locations of the offsite monitoring wells are shown in Figure 3. Locations of the onsite monitoring, extraction, and infection wells are shown in Figure 4 The well inventory of the California Department of Water Resources in Sacramento indicates four wells within one-half mile of the site and 10 wells within one mile (Figure 1) There are no wells that pump water either from a shallow perched zone or from a deeper water-bearing zone within one mile of the site in the downgradient direction. Water supply wells in the area are typically more than 345 feet deep and are screened at depths greater than 144 feet 1.2 SITE HYDROGEOLOGY rThe site is underlain by silty-to-clayey alluvial sediments to a depth of 10-15 feet Below that depth the sediment becomes mostly sandy A thin layer of clay occurs throughout the site at a depth between 25 and 30 feet, but the section again becomes mostly sandy to a depth of about 40 •'■4(T394d91lbi 2