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Atlantic Richfield Company Page 5 isARCO Station No 4932 Stockton Califomia Aagust 29,2002 were measured at 29 and 28 feet bgs,respectively TPHg was detected in four of the ten samples at a maximum concentration of 780 mgfkg (EW-1, 27 5') Benzene was detected in six of the ten samples at a maximum concentration of 5 1 mg/kg (EW-1, 27 5') MtBE was detected in eight of the ten samples at a maximum concentration of 290 mg/kg (EW-1, 27 5') On April 2 through 4, 2002, a step drawdown pumping test, constant rate drawdown pumping test, and aquifer test were completed Results were as follows • Capture zones of approximately 31 feet and 48 feet were calculated in the downgradient and cross-gradient directions, respectively The capture zone was calculated using the Javandel and Tsang method • A pumping rate 4 and 6 gallons per minute was used for the constant rate drawdown pumping test The well installation and aquifer pumping test is documented in SECOR's report titled, Site Assessment and Aquifer Testing Results, dated June 7, 2002 2.3 Geology and Hydrogeology • Geologic cross-sections presented in SECOR's November 9, 2001 report titled Additional Site Assessment Report depict the following conditions • Interbedded layers of sandy silt and silty clay encountered from ground surface to approximately 20 feet bgs • Fine grain sands and silt mixtures from 20 feet bgs to the total depth explored(80 feet bgs) • Groundwater was encountered at approximately 27 feet bgs These conditions are generally consistent with the soils encountered on March 14 and 15, 2002, when West Hazmat installed one deep groundwater monitoring well (DMW-1) and one GYVE well (EW-1) at the site (Figures 2) In each of the borings for wells DMW-1 and EW- 1, soil consisted predominantly of sandy silt from ground surface to approximately 25 feet to 30 feet bgs, with occasional interbedded layers of silty sand Below approximately 25 feet to 30 feet bgs, soils within borings for DMW-1 and EW-1 were comprised of interbedded layers of sandy silt, clayey silt, sand, and silty sand to the total depths explored (81 feet and 50 feet bgs, respectively) Boring logs showing soil stratigraphy are included in Attachment B Updated geologic cross-sections including 6 recently installed extraction and monitoring wells illustrating soil conditions beneath the site are included as Figure 3 Historical cross- sections prepared by SECOR are included in Appendix G Groundwater levels have vaned from approximately 14 feet to 18 feet below mean sea level The general hydraulic gradient at the site has been reported to the east-northeast with a I 1ARCO\49321PAR\PAR doc