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Work Plan for SVE/AS Feasibility Testing ,] E C ® R - _- ARCO Service Station 548 Stockton, California Page 3 of 9 SENSITIVE RECEPTORS A sensitive receptor survey was performed by SECOR in March 2006. According to the Environmental Data Resources Inc (EDR) database sensitive receptor survey report, there are twenty nine (29) water wells located within a one mile radius of the site (EDR, March 23, 2006). Two of these wells are located within a quarter mile of the site (SECOR, 2006). According to the Geotracker database (www.geotracker.swrcb.ca .gov) there are four water supply wells located in the vicinity of the site at an unknown distance. Two wells are owned by the City of Stockton and the other two wells are owned by the County of San Joaquin. In July 2004, URS Corporation (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 two public groundwater production wells within a 2, 000-foot radius of the site. CSPWD identified one active production well within the 2,000400t 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 (gpm) 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 (URS , 2004). CHARACTERIZATION STATUS The site conceptual model prepared by URS (URS, 2004) assumed that the remaining hydrocarbon mass in soil was negligible. This assumption was based on historical soil analytical data , SVE system performance, and the rise in groundwater elevations . The only analytical data indicating that impacted soil was present above 30 feet was collected during the tank excavation in 1998. This data indicates that minor soil impacts existed in the old tank cavity, prior to remediation. SVE wells VW-5S and VW-513 were screened in and below the old tank cavity to remediate soil impacts in the area . These wells were calculated to have a radius of influence of 30 feet (URS , 2004). That radius of influence is large enough to allow VW-5S and VW-51) to remediate soil impacts in and around the tank cavity. In addition , depth to groundwater has increased from approximately 50 feet bgs to approximately 30 feet bgs since site investigations began in 1991 . This rise in groundwater elevations has effectively submerged the impacted soil at the site . The submersion of impacted soil has probably transferred contamination from soil to groundwater, effectively eliminating soil impacts above the former water table. Since SVE/AS operations have removed significant hydrocarbon mass from the site, and groundwater elevations have risen at least 20 feet, impacted soil is no longer considered to be significant to site conditions . Groundwater impacted by petroleum hydrocarbons is generally confined to the area of the UST complex. Non-detectable concentrations of hydrocarbons at MWA through MW-7