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Atlantic Richfield Company Page 16 ARCO Station No 4932,Stockton,California August 29 2002 respectively, GWE from well EW-1,EW-2, and proposed wells EW-3 through EW-7 will control hydrocarbon plume migration 6.4 Conceptual Remedial Alternative Design The goal of this remedial effort is the removal and/or in-situ biodegradation of remaining petroleum hydrocarbons and MtBE in soil and groundwater Based on subsurface site conditions, GWE and SVE should be an effective and cost efficient means of removing TPHg, BTEX, and MtBE from the subsurface soils and groundwater beneath the site Seven wells are recommended for use as GWE wells and nine wells are recommended for SVE (Figure 2) Extraction well EW-1, EW-2, and proposed wells EW-3 through EW-7 will be used for GWE and have been placed based on capture zones calculated from aquifer testing Existing wells SVE-1, MW-1, MW-2, MW-4, EW-1, and EW-2 along with proposed wells SVE-2, EW-3, and EW-4 well be used for SVE Locations are based on vapor radius of influence observed during the DPE feasibility testing Locations of remedial wells are included on Figure 13 This scope of work was selected based on the groundwater flow direction beneath the site and concentrations of TPHg, BTEX, and MtBE reported in the wells Additional recovery wells may be installed and/or connected to the treatment system if necessary,to further control migration of the dissolved petroleum hydrocarbon and MtBE . plume 6.5 Process Flow Submersible electric pumps capable of recovering up to 10 gpm will be utilized in recovery wells EW-1 and EW-2 and proposed recovery wells EW-3 through EW-7 Extracted groundwater will be treated through an air stripper and then through three 2,000-pound GAC vessels in series prior to discharge to the sanitary sewer Influent and effluent groundwater samples will be analyzed and GWE rates will be measured as required for permit compliance and to ensure reliable operation of the system Based on historical soil analytical data, a thermal/catalytic oxidizer will be required to abate extracted vapors The expected destruction efficiency for the abatement equipment will be at least 98 percent The thermal oxidizer will be capable of extracting and treating up to 250 scfm of soil vapor from the extraction wells Influent and effluent petroleum hydrocarbon vapor samples, process temperatures, applied vacuums, and flow rates will be measured as required for permit compliance and to ensure reliable operation of the system I 1ARCO\49321PAR\PAR doc