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Stantec Site History and Previous Investigations Stockton Charter Way Commingled Plume February 15, 2011 respectively. Following UST removal, the facility was demolished. These activities are summarized in the EMCON Results of Underground Storage Tank Removal and Overexcavation Activities dated August 5, 1996. In April and May 1996, EMCON observed ACES as they aerated approximately 300 cubic yards of hydrocarbon-impacted soil. These activities are summarized in the EMCON Completion of Soil Aeration Program dated May 20, 1996. The current property owner; Mr. Bill Halverson, constructed a car wash on the property in 2005. ARCO was asked by the owner to destroy MW-4 to make way for the new car wash. ARCO coordinated the well destruction activities to occur during property development. ARCO took advantage of these activities to coordinate the installation of a remediation system. SVE was conducted between January 1997 and February 1998 to remediate the vadose zone. SVE was terminated after an estimated mass of approximately 10,000 pounds (Ibs) (approximately 1,600 gallons) of TPHg were removed and influent benzene concentrations were less than the laboratory method reporting limits (MRL) of 0.5 milligrams per cubic meter. These activities are summarized in the Pinnacle Environmental Solutions of Cameron Park, California Results of Soil Vapor Extraction Assessment dated April 8, 1998. An AS/SVE system was installed in 2006 and was operated between the fourth quarter 2008 and fourth quarter 2010. The SVE system consisted of 22 vapor extraction wells (EW-1 through EW-17, VW-1, VW-7, VW-8, VW-10, and VW-11), a 15-horsepower vacuum blower, and a 200 cubic ft per minute (cfm) H2 Oil Recovery electric oxidizer (Model H2 CO). The AS system consisted of 22 sparge wells (SP-1 through SP-22) and a 20-hp Rietschle Thomas compressor (Model DLR 300). The AS/SVE system operated for 18,896 hours, removing approximately 4,074 lbs of GRO and 8.91 lbs of benzene. Chevron Facility#9-2033 Chevron operated the station until 1995, when the property was sold to a private dealer and has continued to operate as a Chevron-branded station. In March 1995, Groundwater Technology, Inc. of West Sacramento, California (GTI) installed three groundwater monitoring wells (MW-1 through MW-3) and one soil boring (SB-1) on the property. TPHg and benzene were detected in soil samples collected during the installation activities at concentrations up to 250 and 1.0 mg/kg, respectively. In August 2000, SECOR International Incorporated (SECOR) contracted Precision Sampling of Richmond, California (Precision) to advance three soil borings (SB-2 through SB-4). Cone penetrometer testing (CPT) technology was used to advance SB-3 and SB-4. No soil samples were collected from SB-3/CPT-01 or SB-4/CPT-02. TPHg was detected in soil samples collected from SB-2 at concentrations up to 130 mg/kg. TPHg, benzene, and MTBE were detected in groundwater samples collected from these borings at concentrations up to 42,000, 10,000, and 46,000 pg/L, respectively. These activities are summarized in the SECOR Site Assessment Report dated January 18, 2001. Appendix A- Site History and Previous Investigations.doc 3