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! 0 more readily, the hydrocarbon mass in the silty, clayey soil layers would take a much longer time. Therefore, the overall effectiveness is considered moderate. 4.2.2 Implementability Air sparging/SVE is readily implementable. Besides well installation, the other construction activities are mainly piping and equipment installation. Almost all of the process equipment is commercially ready; some are pre-engineered as package model units to facilitate ease of selection and fabrication, thereby reducing the system fabrication time. With fewer pieces of process equipment than pump -and -treat, the air sparge/SVE system may be installed in an on-site secured area formerly used to house the SVE system, reducing exposure of the system to public view. Permits would still be required for well installation and offgas emissions control device (i.e., the catalytic oxidizer). Liquid collected in the liquid/vapor separator may require pre-treatment with a liquid phase carbon unit prior to discharge to the POTW under a discharge permit. The requirement for multi -permit acquisitions may yet result in a long lead time prior to ' treatment implementation, similar to that for pump -and -treat. Nevertheless, the implementability of this alternative is considered moderate to high. 4.2.3 Cost Major capital and O&M cost items include well and equipment installation, system startup testing, periodic performance monitoring, analytical services and utilities. Assuming some of the existing vapor extraction wells could still be used, the minimum installation cost of an air sparge/SVE system for this site would expect to be around $50,000, plus any additional offgas and entrained liquid treatment needs prior to discharge. The annual field O&M cost would likely be about $50,000 but should be less than that of the pump -and -treat alternative. Overall, the cost effectiveness of this alternative is considered moderate. 4.3 Biosparging Biosparging is another proven technology that has been implemented successfully at many UST sites. This technology is specifically targeted at contaminants that are amenable to aerobic biodegradation, like TPH-g and BTEX, and as such, is therefore potentially applicable and appropriate to address the groundwater contamination at this site. A biosparge system is very similar to an air sparge system, with the primary difference in the amount of air injected into the saturated zone. In biosparging, the amount of air introduced into the groundwater is substantially smaller than in air sparging as the main objective of biosparging is to supply just enough air (or oxygen) to facilitate aerobic biodegradation of the hydrocarbons. In air sparging, on the other hand, as much air as feasible is injected into the subsurface to FS Onsite Petroleum Hydrocarbon Remediation.doc 4-5 Shaw Environmental, Inc.