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a SECTION 5.0 i ALTERNATIVE DEVELOPMENT AND ANALYSIS ' Three remedial alternatives were developed based on the technologies discussed above These alternatives are the most appropriate given site conditions and constraints. The alternatives are 1) air sparging/soil vapor extraction; 2) intrinsic remediation with monitoring; and 3) insitu bioremediation 5.1 ALTERNATIVE I AIR SPARGING/SOIL VAPOR EXTRACTION Alternative Description This alternative consists of installation of a series of extraction and air infection wells within the plume These wells would be connected to a blower/vacuum system via underground piping ' A field pilot study would be necessary to establish the feasibility of the method as well as to obtain information necessary to design and configure the system AS wells would be installed ' into the silt and clay zone and SVE wells would be installed into the upper sandy vadose zone It was assumed that the radius of influence of the AS wells would be approximately 20 to 25-- ? feet To obtain adequate coverage of the plume, about ten AS wells are required Assuming a 50 foot radius of influence, three SVE wells would also be installed Approximately 600 feet of AS piping and 350 feet of SVE piping would be required. Fourteen vaults would be used for well head completion, and the vault where piping enters the treatment compound ' 1Z The treatment unit would be located in the vicinity of the intersection of Sutter Street and Washington Street A carbon unit would be used to strip the volatiles from the SVE stream Because of the small quantities of VOCs present (<400 pounds estimated), small 360 pound carbon scrub units should be adequate for off gas treatment ' Groundwater would be monitored to confirm system performance and to track plume location Groundwater wells to be monitored would consist of source area wells (MW-2 and MW-2A) to confirm that concentrations were decreasing as anticipated, downgradient well MW-7 to confirm that the leading edge of the plume is not significantly expanding and unimpacted wells (MW-3, MW-6, and MW-9) to confirm that the plume does not migrate Groundwater samples would be analyzed for BTEX and TPH-G One deeper monitor well (screened at 65 to 75 feet bgs)—? would be installed If the water table continues to rise or maintains its present level, one shallow well screened across the water table would be installed in the vicinity of MW-2A 1 Evaluation ' Effectiveness The effectiveness of this alternative depends on the air permeability of the silty- clay layer (Zone 4) Although the groundwater surface currently intersects Zone 3, in the past, LTROI ECTSZANJ OQUiSA\ACnON PL 36