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Remedial Action Plan and Further Site Assessment 6 7-Eleven Store No 19976 1399 N Main St Manteca CA May 30 2000 Equipment required for vapor extraction/air sparging Includes a positive-displacement blower or air compressor, in addition to equipment required for vapor extraction The treatment efficiency of air sparging as a remediation process is variable, with up to 90 - 95 percent reductions in dissolved levels (from initial concentrations)reported using this form of remediation There is as yet no well-established track record of this treatment method for MTBE, but pilot tests (ACS Convention,April 2000) demonstrate limited success in mass transfer of MTBE from the liquid to the vapor phase by conventional sparging Heated air sparging may likely prove more effective in overcoming the high solubility of MTBE, but safety issues regarding treatment of mobile flammable vapors such as gasoline would need to be addressed prior to application Carbon adsorption can be used to treat extracted soil vapors at an efficiency of up to 99 percent Also commonly used during soil vapor extraction/air sparging is one of the incineration processes (either catalytic oxidation or thermal oxidation) Catalytic oxidizers are used to destroy hydrocarbon vapors during soil vapor extraction, and operate most cost-efficiently at moderate vapor concentrations of 5- 25 percent of the lower explosive limit (LEL) (700 - 3,500 parts per million by volume (ppm(v))) Catalytic oxidizers are capable of destroying at least 95 percent of extracted hydrocarbon vapors within their optimum concentration operating range At concentrations higher than the maximum capacity of the equipment, dilution is required At concentrations of less than 5 percent LEL, auxiliary electricity is required Thermal oxidizers are used to destroy hydrocarbon vapors during soil vapor extraction, and operate most cost-efficiently at concentrations ranging from 25-60 percent LEL (3,500- 8,400 ppm(v)) Thermal ' oxidizers have a destruction efficiency of at least 95 percent At influent concentrations of more than 60 percent LEL, dilution is required At concentrations of less than 60 percent LEL, auxiliary fuel (natural gas) is required In varying amounts (more is required as concentrations decrease) Both catalytic and thermal oxidizers require electricity to operate, and thermal oxidizers require natural gas for combustion Although MTBE is not currently regulated by local air boards, it is anticipated that It will be sometime prior to the end of the cleanup period Therefore, the offgas treatment system will be designed to destroy MTBE vapors in addition to traditional petroleum constituents As an augmentation to groundwater extraction, this remediation method could be implemented upgradient of the extraction point, potentially reducing dissolved hydrocarbon concentrations prior to removal by the 1