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Remedial Action Plan and Further Site Assessment 5 7-Eleven Store No 19976 1399 N Main St Manteca CA May 30 2000 40 FEASIBLE SUPPLEMENTAL REMEDIATION ALTERNATIVES One of the remediation alternatives which is always evaluated for any site is the possibility that no further _ action is required The SJCPHS has already indicated that this is not an option for this site ' Another remediation alternative which will not be evaluated in detail is natural biodegradation/attenuation Dissolved MTBE does not generally respond well to intrinsic (unassisted) biodegradation, and attenuation as a treatment method is invalidated by the SJCPHS's request for active plume control measures ' Remediation pilot testing has not yet been conducted at this site Technical and logistic feasibility assumptions are based on application of typical data from sites with similar lithologylhydrology and retail setting Site-specific response to the remediation process will be verified after implementation of plume capture If the remediation method requires modification based on site-specific data, the system will be ' adjusted to achieve maximum effectiveness All system adjustments and/or modifications will be discussed with the SJCPHS prior to implementation Three conceptually-feasible remediation alternatives in addition to groundwater extraction as a plume control method were considered for hydrocarbon cleanup at the site with relation to time and cost, to evaluate which method or combination of methods would be most cost effective The methods considered were vapor extraction and air sparging, electrokinesis, and enhanced intrinsic biodegradation ' 41 Vapor Extraction/Air Sparging ' Soil vapor extraction involves the application of negative pressure to the vadose zone to remove hydrocarbon vapors from the soil Air sparging involves the injection of air beneath the subsurface ' (usually about 5 feet below the top of the water table)to physically desorblvolatilize hydrocarbons from soils and groundwater in the saturated zone A byproduct of the process is improvement of natural biodegradation processes through the delivery of additional oxygen to microorganisms below the water ' table Air sparging is normally done in conjunction with vapor extraction, which is used to capture the vapors generated by the sparging process Air sparge point spacing is inversely proportional to ' permeability(i a for sands, the points should be spaced about 10 feet apart, and about 15 feet for silts) Vapor extraction point spacing is directly proportional to permeability(i a spacing should be 40 feet apart ' for sands, and 20 - 30 feet apart for silts) 1