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Report on Additional Site Assessment and Soil Vapor Extraction Test 5 <br /> 16 7-Eleven Store No 17334 4501 North Pershing Avenue,Stockton,CA August 21,2002 <br /> ' Five SVE samples were collected in Tedlar bags and submitted for laboratory analysis Highest benzene <br /> concentrations were detected in the vapor sample extracted from well MW-5A at 18 ptg/L Highest TPH-G <br /> was reported in the sample from well SPV-1 MTBE concentrations ranged from 55 µg/L in the sample <br /> ' from MW-5A to 140 gg/L in one of three samples collected from well SPV-2 Air sample analytical results <br /> are summarized in Table 3A <br /> ' 60 CONCLUSIONS AND RECOMMENDATIONS <br /> ' The vertical extent of the dissolved MTBE plume has been generally delineated by attenuated MTBE <br /> concentrations of 67 µg/L in the water sample collected at 50 feet bg in boring SB-1, and non-detectable <br /> MTBE levels in source well MW-58 (screened 38-40 feet bg) Well MW-513 is considered adequate for <br /> ' continued monitoring of deeper plume concentrations, and no additional vertical delineation is proposed <br /> SVE may be useful in removing vadose-zone contaminants, and well MW-5A is positioned appropriately <br /> to remove hydrocarbons/oxygenates related to the former UST area The sparge segments of wells <br /> SPV-1 and SPV-2 can be used for oxygen injection to enhance intrinsic aerobic biodegradation, or for <br /> ozone infection to destroy hydrocarbons/oxygenates below the soiltwater interface Both of these <br />' potential remediation alternatives will be evaluated (under separate cover following submittal of a <br /> remedial action proposal) if remediation is required at this site by the SJCPHS <br /> Consistently higher dissolved MTBE concentrations in offsite downgradient well MW-4 as compared to <br /> source well MW-5A, reported consistently based on quarterly data obtained during the last two years, <br /> Indicate a possible offsite source (i e , the Cardlock facility) of MTBE In the vicinity of well MW4 An <br /> agency file search may be pursued to investigate this potential <br /> Additional downgradient lateral delineation is being pursued, but potential new well locations are on <br /> private property, and access is still in negotiation <br /> Additional offsite drilling Is scheduled to be conducted late third quarter 2002 <br /> Groundwater monitoring well analytical data and groundwater flow directions are discussed in the <br /> quarterly monitoring reports <br /> 1 <br /> 1 <br /> 17334sardoc <br />