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Third Quarter 2002 Monitoring,Sampling,and Remediation Progress Report 3 16 7-Eleven, Inc, Store#19976 1399 North Main Street Manteca,CA October 31 2002 Upon receipt of these data, the SJCPHS requested further lateral delineation Well MW-6 was installed in December 1999, to a depth of 30 feet bg (Figure 2) Sod samples collected during well installation contained no detectable benzene or MTBE, and up to 15 4 mg/kg TPH-G, with the highest levels detected at 20 feet bg (capillary fringe soils) Sod hydrocarbonfoxygenate delineation is considered complete at this time On September 18, 2000, as requested by the SJCPHS, eleven soil-gas survey points were pushed to 3 feet bg Significantly elevated MTBE concentrations (2,200 dig/L)were detected in only one of the points ' (SG-9), located along the western edge of the UST pit about 20 feet south of MW-2 On November 1, 2000, monitoring well MW-7 was installed to a depth of 30 feet bg and soil boring SB-2 was drilled to a depth of 50 feet bg (Figure 2) All soil samples analyzed from both well MW-7 and soil boring SB-2 were non-detectable for BTEX, TPH-G, and MTBE A grab groundwater sample was collected from boring SB-2 at a depth of 40 feet bg Upon analysis, the results were non-detectable for all analyzed constituents, except for total xylenes, which were detected at a concentration of 1 5 pg/L SVE testing conducted in 2001 using the two horizontal vent wells installed in the former UST tank pit (IT Corporation, September 2001) indicated extracted vapor concentrations of over 10,000 parts per million by volume (ppm[v]) at applied vacuums ranging between 9 and 32 inches of water(IW) Induced vacuum responses of more than 0 2 IW were observed in wells MW-1, MW-2, and MW-3 during extraction from the horizontal wells Vacuum response in these wells is likely facilitated by relatively higher-permeability conditions in the tank cavity backfill as opposed to native soils Testing was also conducted on the ' groundwater monitoring wells, lower permeability and limited screen above the water table likely account for low extraction rates/low induced vacuum responses observed during extraction from the wells ' Extracted vapor concentrations ranged up to 0 91 ppm(v) benzene, 220 ppm(v) MTBE, and 880 ppm(v) TPH-G The data indicated that vapor extraction is a viable remediation method at the site, particularly when the horizontal wells are used Double-nested sparge well SP-1 was installed on October 29-30, 2001 to a depth of 50 feet bg and perforated at 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 infection Pre-sparging extracted vapor levels ranged up 1,000 ppm[v], with dissolved oxygen (DO) levels of up to 0 72 mg/L Airwas 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 ppm(v), and DO levels to 8 mg/L, after 30 minutes of sparging The data indicated the area of sparging influence in SP-1 includes 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 MW-1A as the injection point and the horizontal wells as the SVE point Results indicated no breakthrough of sparged air into the vadose zone accessible by the horizontal wells 1 19976Q23 DOG