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Stantec U December 8, 2010 Page 3 of 9 Double-nested sparge well SP-1 was installed on October 29 to 30, 2001 to a depth of 50 feet bgs and screened from 30 to 35 and 45 to 50 feet. On February 6, 2002, an air sparge test was conducted using well MW-2 for vapor extraction, and double-nested sparge well SP-1 for air injection. .Pre-sparging extracted vapor levels ranged up 1,000 ppmv, with dissolved oxygen (DO) levels of up to 0.72 mg/L. Air was then injected into the deeper section of well SP-1 using an oil-less air compressor. Vapor levels in well MW-2 increased to 1,600 ppmv, and DO levels to 8 mg/L, after 30 minutes of sparging. The data indicated the area of sparging influence in SP-1 included the region of MW-2, and that treatment using well SP-1 should be successful at reducing dissolved hydrocarbons/oxygenates in well MW-2 and the surrounding area. Air sparge testing was repeated on May 23, 2002, using well MWAA as the injection point, and the horizontal wells as the SVE points. Results indicated no breakthrough of sparged air into the vadose zone accessible by the horizontal wells. On May 27, 2003, one soil sample was collected under the northern fuel dispenser, and a second sample was collected beneath the product line during a fuel system upgrade. The soil samples collected beneath the dispenser and fuel delivery piping did not contain concentrations of TPHg, BTEX, or fuel oxygenates above laboratory detection limits. On June 9, 2003, three 10,000-gallon double-walled fiberglass USTs were removed from the excavation and hauled offsite. On June 9 and 19, 2003, a total of six UST confirmation soil samples (T1 N-15' through T3S-13') were collected in native soil underlying the ends of the three USTs (Figure 2) at approximate depths of 12 to 15 feet bgs during the second UST replacement event at the site. TPHg, BTEX, and fuel oxygenates were not detected at concentrations above laboratory detection limits in two of the six soil samples collected beneath the USTs. Benzene and TPHg were reported in the soil samples collected beneath the north ends of two USTs (T1 N, T2N) at maximum concentrations of 0.0087 mg/kg and 9.3 mg/kg, respectively. MtBE and TBA were reported at maximum concentrations of 3.3 mg/kg (T1 N@13') and 18 mg/kg (TXN@13'), respectively. Between June 23 and July 7, 2003, Glacier Environmental Services installed two new double- walled fiberglass USTs: one 10,000-gallon premium unleaded gasoline UST, and one 15,000- gallon regular unleaded gasoline UST, and associated piping and dispensers (Figure 2). In order to accommodate the new 15,000-gallon UST, Glacier excavated approximately 288 cubic yards of soil, expanding the UST pit to the west. The excavated soil was disposed of at Forward Inc. landfill. During the installation of the new UST's in July 2003, SECOR International Inc. (SECOR) personnel extended the horizontal extraction line in the tank pit to the east to terminate in the well box of SPA. Half inch tubing was run from the junction box in the planter to SPA to facilitate oxygen injection away from the dispenser islands. On April 9, 2004, SECOR submitted a request with the SJCEHD to reduce sampling of MW-4 and MW-4A from quarterly to annually. Approval was received in a letter from the SJCEHD dated July 28, 2004. On June 2, 2004, a 22-hour SVE event was conducted on the horizontal tank pit wells. Based on soil vapor samples collected during the test it is estimated that approximately 0.10 pound of TPHg was removed in soil vapor during the 22-hour test. No recordable amount of benzene or MtBE was removed during the test. 19976 Vapor Risk Assessment Report.doc