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Stantec Site History and Previous Investigations Stockton Charter Way Commingled Plume No. CP0057 November 15, 2011 In April 2007, ETIC Engineering, Inc. of Pleasant Hill, California (ETIC) performed a water well survey within 2,000 ft of the property. The Environmental Data Resources (EDR), the California Department of Water Resources (DWR), and Cal Water were contacted to identify water supply wells in the vicinity. EDR identified one public well (W1 — located at V&P Trailer Park; approximately 2,000 ft northeast of the property)within the search radius. DWR had no records for agricultural, domestic, industrial, or municipal water supply wells within the search radius. Cal Water indicated that they did not have a well within the search radius via a telephone call and fax communication. The location of W1 could not be verified during the field visit performed on March 13, 2007. Between April and July 2007, ETIC contracted Gregg to advance 11 soil borings (Cl through C11) and installed four groundwater monitoring wells (MW-1A through MW-4A). TPHg, benzene, and MTBE were detected in soil samples collected during the installation activities at concentrations up to 5,500, 38, and 1.5 mg/kg, respectively. TPHg, benzene, and MTBE were detected in groundwater samples collected from these borings at concentrations up to 400,000, 26,000, and 1,700 pg/L, respectively. These activities are summarized in the ETIC Soil and Groundwater Investigation Report dated October 2007. In April 2008, PSC Environmental Services of Columbia, Illinois (PSC) contracted Gregg to advance eight CPT borings (CPT-M4 through CPT-M11) to further delineate the vertical and lateral extent of petroleum hydrocarbon impacts and evaluate hydrogeologic conditions in the deeper water bearing zones beneath the property. No analytes were detected above their respective laboratory MRL. These activities are summarized in the PSC Subsurface Investigation Report dated July 31, 2008. In January 2009, PSC contracted TEG-Northem California to install eight soil gas sample locations (SG-TEST and SG-1 through SG-7) to evaluate the need for soil vapor intrusion. No soil samples were collected during the installation activities. These activities are summarized in the PSC Vapor Intrusion Survey— Soil Gas Sampling Report dated March 31, 2009. In June 2009, PSC supervised Gregg to install two groundwater monitoring wells (CT-MW-8-87 and CT-MW-9-120) and advanced one soil boring (CT-8-130)to further delineate the vertical and lateral extent of petroleum hydrocarbon impacts beneath the property. Benzene and MTBE were detected in soil samples collected during the installation activities at concentrations up to 0.18 and 0.0064 mg/kg, respectively. These activities are summarized in the PSC Monitoring Well Installation and Bio Sparge Evaluation Report dated December 3, 2009. A groundwater monitoring and sampling program has been in place at this property since January 2007. Remediation Activities In February 1994, the two 4,000-gallon gasoline USTs and the fuel dispenser were removed for permanent closure. During the UST removal, the San Joaquin Health District inspector noted three 1/2-inch diameter holes on the bottom of the southern UST. No record is available to confirm whether the associated UST system piping was removed during the closure activities. Following removal, four soil samples (TK1W, TK1E, TK2W, and TK2E) were Stockton Charter Way Site History and Previous Investigations.doc 6