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Multi-Phase Extraction Pilot Test Report& Remedial Design Thrifty Station No 171 Page 1 Stockton,California November 30,2010 1.0 INTRODUCTION Environ Strategy Consultants, Inc. (Environ Strategy), on behalf of Thrifty Oil Co., is pleased to present this Multi-Phase Extraction Pilot Test Report & Remedial' Design for the property located at 1250 North Wilson Way in Stockton, California(the site). Pilot testing was conducted from October 25, 2010 to October 30, 2010 in accordance with the regulatory-approved Groundwater Extraction Pilot Test Work Plan (Workplan), dated May 24, 2010, and approval letter from the San Joaquin County Environmental Health Department,dated August 18, 2010. The site is located on the corner of East Harding Way and North Wilson Way in Stockton, California(Figure 1). The site is currently operating as an active retail gasoline station. The site includes three gasoline dispenser islands overlain by a canopy, and one.cashier kiosk. The site configuration is illustrated in Figure 2. From October 25, 2010, to October 30, 2010, a Multi-Phase Extraction (MPE) pilot test was conducted at the site to determine effectiveness of MPE system operation for the remediation of the soil and groundwater at the site. Pilot test extraction was conducted from three wells individually during the first three days and in combination the last two days. A site plan showing the boring locations and extraction well locations is provided as Figure 2. The general sets of data acquired during this MPE pilot test were: system operational parameters, including vacuum, flow, and influent hydrocarbon concentrations, and depth to water and vacuum response measurements from adjacent monitoring wells. Activities and results associated with the MPE pilot testing are described in further detail in subsequent sections. 2.0 MPE PILOT TESTING MPE pilot testing was performed onsite from October 25, 2010 to October 30, 2010,using three extraction wells: EW-5S, EW-5D, and TB-7, the screen intervals for these wells are 40'-60', 65 - 85', and 25'-75', respectively. Operational parameters, including system vacuum, flow and pressure,were recorded during the test to evaluate system performance and effectiveness. In order to determine effective radius of influence, negative pressure response is monitored and recorded in adjacent wells. A summary of operational data collected during testing is included as Tables 1 through 4. Field data sheets are attached in Appendix A. Negative pressure response was measured using vacuum gauges. A negative pressure reading exceeding 1% of the applied vacuum (or at least 0.1 inch of water) is considered to be indicative of effective vacuum influence. Vacuum response data is also included in Tables Y through 4. environ strategy consultants, inc.�