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<br /> 7-Eleven Store#19976
<br /> Quarterly Groundwater Monitoring and Remediation Progress Report(2Q2003)
<br /> September 11, 2003
<br /> Page 3
<br /> maximum TPHg concentration in soil was reported at 20 feet bgs (15 4 mg/kg) Delineation of
<br /> hydrocarbons adsorbed to sod is considered complete at this time (Shaw, 2000)
<br /> On September 18, 2000, as requested by the SJCPHS, eleven soil-gas survey points were pushed
<br /> to 3 feet bgs Significantly elevated MtBE concentrations (2,200 pg/L) were detected in only one of
<br /> the points (SG-9), located along the western edge of the UST pit about 20 feet south of MW-2 '
<br /> On November 1, 2000, monitoring well MW-7 was installed to a depth of 30 feet bgs and soil boring
<br /> SB-2 was drilled to a depth of 50 feet bgs (Figure 2) Soil samples analyzed from both well MW-7
<br /> and soil boring SB-2 did not contain BTEX, TPHg, and MtBE above laboratory reporting limits A
<br /> grab groundwater sample was collected from boring SB-2 at a depth of 40 feet bgs Total xylenes
<br /> were detected at a concentration of 1 5 NgIL
<br /> SVE testing conducted in 2001 using the two horizontal vent wells installed in the former UST tank
<br /> pit (IT Corporation, September 2001) indicated extracted vapor concentrations of over 10,000 parts
<br /> per million by volume (ppmv) at applied vacuums ranging between 9 and 32 etches of water
<br /> Induced vacuum responses of more than 0 2 inches of water were observed in wells MW-1, MW-2,
<br /> and MW-3 during extraction from the horizontal wells Vacuum response in these wells is likely
<br /> facilitated by relatively higher-permeability conditions in the tank cavity backfill as opposed to native
<br /> soils Testing was also conducted on the groundwater monitoring wells, lower permeability and
<br /> limited screen above the water table likely account for low extraction rates/low induced vacuum
<br /> responses observed during extraction from the wells Extracted vapor concentrations ranged up to
<br /> 0 91 ppmv benzene, 220 ppmv MtBE, and 880 ppmv TPHg The data indicated that vapor extraction x
<br /> is a viable remediation method at the site, particularly when the horizontal wells are used
<br /> Double-nested sparge well SP-1 was installed on October 29-30, 2001, to a depth of 50 feet bgs and
<br /> perforated at 30-35 and 45-50 feet On February 6, 2002, an air sparge test was conducted using
<br /> well MW-2 for vapor extraction, and double-nested sparge well SP-1 for air injection Pre-sparging
<br /> extracted vapor levels ranged up 1,000 ppmv, with dissolved oxygen (DO) levels of up to 0 72 mg/L
<br /> Air was then infected into the deeper section of well SP-1 using an oil-less air compressor Vapor
<br /> levels in well MW-2 increased to 1,600 ppmv, and DO levels to 8 mg1L, after 30 minutes of sparging
<br /> The data indicated the area of sparging influence in SP-1 includes the region of MW-2, and that
<br /> treatment using well SP-1 should be successful at reducing dissolved hydrocarbons/oxygenates in
<br /> well MW-2 and the surrounding area Air sparge testing was repeated on May 23, 2002, using well
<br /> MW-1A as the infection point and the horizontal wells as the SVE point Results indicated no
<br /> breakthrough of sparged air into the vadose zone accessible by the horizontal wells
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<br /> On May 27, 2003, one sod sample was collected under the northern fuel dispenser(D14 5), and the �s
<br /> second sample was collected beneath the product line (1-1-4 0) during a fuel system upgrade The 5,1
<br /> soil samples collected beneath the dispenser and fuel delivery piping did not contain concentrations ;
<br /> of TPHg, BTEX, or fuel oxygenates above laboratory detection limits A soil sample was unable to
<br /> be collected from beneath the southern dispenser due to an excessive thickness of pea gravel On R
<br /> June 9, 2003, three 10,000-gallon double-walled fiberglass USTs were removed from the excavation `se,
<br /> and hauled offsite ,
<br /> On June 9 and 19, 2003, a total of six UST confirmation soil samples (T1N-15' through T3S-13')
<br /> were collected in native soil underlying the ends of the three USTs (Figure 2) at approximate depths
<br /> of 12 to 15 feet bgs TPHg, BTEX, and fuel oxygenates were not detected at concentrations above
<br /> laboratory detection limits in two of the six soil samples collected beneath the USTs Benzene and
<br /> 40 TPHg were reported in the soil samples collected beneath the north ends of two USTs (T1 N, T2N) at
<br /> 19976 03-2Q Report doc SECOR International Incorporated
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