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Stantec Site History and Previous Investigations Stockton Charter Way Commingled Plume February 15, 2011 1998. United Gas placed new USTs in the former UST pit location and operated the service station between 1999 and 2004. During 2004, the station brand switched to ARCO. In May 1989, GTI advanced four vertical soil borings (SB-1 through SB-4) and one angle soil boring (AB-3) on the property. Between May 1989 and May 1990, GTI installed seven groundwater monitoring wells (MW-1 through MW-7) on the property and four groundwater monitoring wells (MW-8 through MW-11) off of the property. TPHg and benzene were detected in soil samples collected during the installation activities at concentrations up to 2,500 and 11 mg/kg, respectively. These activities are summarized in the GTI Environmental Assessment Status Report dated October 9, 1990. In September 1993, GTI installed five groundwater monitoring wells (MW-13 through MW-17) off of the property. TPHg and benzene were detected in soil samples collected during the installation activities at concentrations up to 3.7 and 0.23 mg/kg, respectively. These activities are summarized in the GTI Summary Report of Drilling Activities dated December 16, 1993. In November 2000, Cambria advanced four cone penetrometer testing (CPT) borings (CPT-1 through CPT-4) to further assess the vertical and horizontal extent of petroleum hydrocarbons beneath the property. TPHg and benzene were detected in soil samples collected during the CPT testing activities at concentrations up to 3,150 and 24.7 mg/kg, respectively. TPHg and benzene were detected in groundwater collected from these borings at concentrations up to 109,000 and 31,300 micrograms per liter (pg/L), respectively. These activities are summarized in the Cambria Site Investigation Report dated December 20, 2000. In October and November 2001, Cambria advanced three CPT borings (CPT-5 through CPT-7) to further assess the vertical and horizontal extent of petroleum hydrocarbons beneath the property. TPHg and benzene were detected in soil samples collected during the CPT testing activities at concentrations up to 47,000 and 19,000 mg/kg, respectively. Well MW-16 was properly destroyed on November 15, 2001. These activities are summarized in the Cambria Site Investigation Report dated December 13, 2001. In August 2002, Cambria installed three B zone (MW-11-82, MW-18-80, and MW-19-81) and three C zone (MW-11-122, MW-18-120, and MW-19-120) groundwater monitoring wells to evaluate the water zones beneath the property. No soil samples were collected from these borings. These activities are summarized in the Cambria Site Investigation Report / Groundwater Monitoring Report— Third Quarter 2002 dated October 2, 2002. In August and September 2004, Cambria advanced two CPT borings (CPT-8 and CPT-9) to further assess the vertical and horizontal extent of petroleum hydrocarbons beneath the property. TPHg and benzene were detected in soil samples collected during the CPT testing activities at concentrations up to 74 and 0.035 mg/kg, respectively. TPHg and benzene were detected in groundwater samples collected from these borings at concentrations up to 27,000 pg/L and 11,000 pg/L, respectively. These activities are summarized in the Cambria Site Investigation Report, Site Conceptual Model, and Work Plan dated November 15, 2004. In October 2005, Cambria installed two B zone (MW-3-79 and MW-10-81) and two C zone (MW-3-119 and MW-10-117) groundwater monitoring wells to further assess the vertical and horizontal extent of petroleum hydrocarbons beneath the property. No soil samples were Appendix A- Site History and Previous Investigations.doc 7