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S E C 0 R Conceptual Site Model Chevron Service Station#9-6171 March 25, 2005 Page 13 exposure to petroleum hydrocarbon affected soil Natural attenuation is the BAT because the Chevron service station is downgradient from active water wells In addition, the monitoring results will document the presence of intrinsic biodegradation This tracks contaminant concentrations through continuous remediation until action levels are met I52 Chlorinated Compound Remediation Based on the analytical results and site characterization by Levine-Fricke-Recon, Inc (LFR), requested by the Califomia Regional Water Quality Control Board (RWQCB) and the SJCDEH, a self-contained remediation system is operated by LFR for the landowner of the LVSC, Lincoln Properties, Ltd The groundwater extraction system's treatment compound is located on the northeast corner of Douglas Avenue and Gettysburg Place This location corresponds to the southwest corner of the LVSC property, adjacent to the south wall of Rite Aid The primary purpose of this remediation system is to remove chlonnated solvents from the groundwater However, it is likely that hydrocarbon contamination commingled with the chlorinated solvent plume is being remediated by the treatment system described below Based on LFR results of the Health Risk Assessment (HRA), it was determined that • remedial activities at LVSC are necessary to reduce PCE concentrations in both soil vapor and groundwater to mitigate estimated health risks These Interim Remedial Actions (IRAs) were implemented in three different phases and are still in operation today 52.1 Phase I —Groundwater Extraction System, 1998 to Present The objective of the Phase I Groundwater Extraction System (GWETS) is to prevent the off- site migration of hazardous substances in groundwater within the A-Zone Aquifer The GWETS consists of 17 A-Zone Aquifer groundwater extraction wells (GEW-1 to GEW-17) spaced at approximately 100-foot intervals along the eastern property boundary of the LVSC, adjacent to Pacific Avenue Two of these groundwater extraction wells, GEW-007A and GEW-008A, are located on the Chevron property The groundwater is pumped via a double walled conveyance pipeline that connects the 17 groundwater extraction wells to the Treatment System Compound (TSC) Water that is pumped into the TSC is treated using an air stripper and two liquid-phase carbon-adsorption canisters Treated water is then discharged into a storm drain inlet located within the compound fencing Vapor discharged from the air stripper is treated using two vapor-phase carbon canisters Treated air is then discharged to the atmosphere The details of the construction activities can be found in the Phase I IRA Detailed Plan (LFR 1998a) 5.2.2 Phase II —Soil Vapor Extraction System, 1999 to Present The objective of the Phase II Soil Vapor Extraction System (SVETS) is to reduce the mass of detected hazardous substances in the vadose zone soils within the source area The N Tiles\Proiects\Chevron\Retail\##9-6171\Site Conceptual ModelTINAL_CSM doc