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�l - I ' Ms. Lori Duncan Page 2 San Joaquin County Environmental Health Department January 28, 2005 l� An SVE/AS system consisting of six SVE wells and three AS wells began operating in September 2000. The system was operated nearly continuously through June 2004. Low influent concentrations prompted the shutdown of the SVE system in June 2004. To date the SVE system has removed approximately 2,000 pounds (lbs) of petroleum hydrocarbons from the subsurface. In addition, 7 gallons (43.17 lbs) of 1 free product have been removed from site wells. In July 2004, URS conducted a file review at the Department of Water Resources (DWR) and City of Stockton Public Works Department (CSPWD) to identify wells within a radius of 2,000 feet from the site and a sensitive receptor survey to identify all potential receptors within a 500-foot radius. DWR records identified 12 domestic wells and 2 public groundwater production wells within a 2,000-foot radius of the site. CSPWD identified one active production well within the 2,000-foot radius. The production well is City Well # 1, located approximately 950 feet south-southeast of the site. This well produces approximately 800 gallons per minute and is screened at various intervals between 170 and 240 feet below ground surface (bgs). The sensitive receptor survey did not identify any surface water bodies,child-care centers, schools, or wildlife habitats within 500 feet of the site. ASSESSMENT ACTIVITIES AND FINDINGS Between December I and 2, 2004, two 2-inch-diameter groundwater monitoring wells (MW-7 and MW-8) were installed to monitor the lateral and vertical extent of groundwater impacts at the site (Figure 2). Monitoring well MW-7 is located offsite across the street in the down-gradient groundwater flow direction. MW-7 was installed to allow for monitoring of shallow groundwater. Monitoring well MW-8 was installed on-site just east of the USTs to monitor deep groundwater. Monitoring wells were drilled and installed by Cascade Drilling of Rancho Cordova, California, with a hollow-stern auger (HSA)-equipped drill rig using 8.25-inch-outside-diameter(OD) augers. i� Presented below is a discussion of subsurface conditions; soil sampling and analysis; waste storage and disposal; groundwater monitoring well installation, development, sampling and surveying; soil analytical data; and groundwater analytical data. Subsurface Conditions Soils encountered during drilling consisted primarily of poorly graded sands, silty sands, and silt. The depth interval from 1 to approximately 10 feet bgs is fill material. The depth interval from approximately 10 to 30 feet bgs is dominated by silty and, The depth interval from approximately 30 feet to 35 feet bgs is dominated by sand. The depth interval from approximately 35 to 65 feet bgs is dominated by silt. The depth interval from 65 to 100 feet bgs consists of clayey silt interbedded with silty sand. A URS geologist classified the soils using the Unified Soil Classification System. Boring logs are presented as Attachment B. 1 K:1Wprocess\T5 BP ARCD100548\2004 well instail\Add Site Assess Rpt 04.doc