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I i{ City of Stockton TL# 394-0192-01 September 16, 1994 Page 3 Ij anticipated at approximately 15 feet BSG, and the regional flow direction for the' Stockton area is towardjthe east. However, recent excavation work at the site indicat . es that the current depth to groundwater exceeds 19.5 feet BSG (see below) . Local groundwater flow may be influenced by pumping of water wells and recharge from various sources. The effect of these influences on groundwater beneath the site is beyond':'i, the scope of this investigation. �? i it 3.3 Project History Twining understands that a 500-gallon gaso{line] UST was removed from the site. in 1993 and that the excavation was � deepened to 19.5 feet BSG in July 1994. According to a McCampb',ell Analytical Inc. laboratory report dated July 8, 1994, analysis of a soil sample collected from 19.5 feet BSG detected 891 milligrams per kilogram (mg/kg) TPH-G, 1 mg/kg toluene, 1 mg/kg ethylbenzene, and 8. 5 mg/kg xylenes. According to the laboratory report, benzene was not detected above the method detection limit. i 4.0 PROPOSED INVESTIGATIVE PROCEDURES This groundwater assessment will consist of afield investigation, laboratory analysis, and preparation of altechnical report. These activities are summarized in the following subsections. Standard operating procedures (SOPS) , relevant to 'the 'field and laboratory activities, are described in Appendix A. °1 4. 1 Field Inve,stiaation it Twining proposes to drill three soil borings using a CME-75 truck- mounted drill rig equipped with 7-5/8-inch diameter hollow-stem augers (Drawing No. 2) . Each boring willj�be hand augered to three feet jBSG prior to drilling and will be advanced to 10 feet below the bottom of soils containing field evidence of petroleum product constituents (PPCs) or groundwater, whichever occurs first. A Twining geologist will log the soils in accordance with the Unified Soil Classification System. 4.1.1 Soil Boring Locations and Soil Samplinq Criteria r Twining proposes to drill three soil borings to an estimated depth of approximately 40 feet BSG. One soil{ boring will be drilled through the approximate center of soils containing PPCs to assess the vertical extent of gasoline in soil. The remaining two borings will be placed approximately 10 feet to the east and 15 feet to the north to assess the local groundwater flown direction and to attempt a :l i.