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7-Eleven Store #19976 Quarterly Groundwater Monitoring and Remediation Progress Report (2Q2006) August 8, 2006 Page 4 Extracted vapor concentrations ranged up to 0 91 ppmv benzene, 220 ppmv MtBE, and 880 ppmv TPHg The data indicated that vapor extraction was a viable remediation method at the site, particularly when the horizontal wells were used Double-nested sparge well SP-1 was installed on October 29-30, 2001 to a depth of 50 feet bgs and screened from 30-35 and 45-50 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-spargmg extracted vapor levels ranged up 1,000 ppmv, with dissolved oxygen (DO) levels of up to 0 72 mg/L Air was then infected 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 spargmg 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 q, surrounding area Air sparge testing was repeated on May 23, 2002, using well MW-1A as the infection 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 9�1�4d 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 (T1N@13') and 18 mg/kg (TA@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 personnel extended the horizontal extraction line in the tank pit to the east to terminate in the well box of SP-1 Half inch tubing was run from the function box in the planter to SP-1 to facilitate oxygen infection • away from the dispenser islands 19976 06-20 Report doc SECOR International Incorporated