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i <br /> 1 <br /> E <br /> 3.3.4 Alternative 4 - Soil Vapor Extraction/Air Sparging with Groundwater <br /> Monitoring <br /> o Criterion 1 <br /> This alternative has minimal health-based risks Gasoline hydrocarbons are removed <br /> ' from extracted prior vapor to release t <br /> P p o the atmosphere eliminating the risk of <br /> exposure to humans Groundwater would be monitored periodically to ensure that <br /> ' continuing degradation of existing or potential beneficial uses is declining Potential <br /> fire or explosion hazard exists due to the relatively high levels of documented <br /> residual hydrocarbons, but would be significantly reduced with a properly designed <br /> l ' system and regularly scheduled monitoring and maintenance <br /> ' 0 Criterion 2 <br /> Vapor extraction should reduce the level of toxicity, mobility and volume of <br /> ' contaminants in the soil to levels acceptable to regulatory agencies Pilot testing <br /> indicates vapor extraction to be a feasible alternative for remediation of the site No <br /> air sparge pilot test was performed, but the relatively high permeability soil type <br /> observed during drilling of monitoring wells at the site, and documented results at <br /> i sites with similar soil type indicates that air sparging may be a technically feasible <br /> remedial alternative for remediation of the site when combined with vapor <br /> extraction <br /> o Criterion 3 <br /> This alternative can be implemented within regulatory guidelines <br /> i <br /> o Criterion 4 <br /> A thermal oxidizer is recommended for treatment of offgases due to high initial <br /> contaminant influent concentrations observed during the vapor extraction test <br /> Resulting capital outlays compared to other off-gas abatement equipment would be <br /> E higher, but use of less efficient offgas abatement equipment is not recommended <br /> Significant additional costs to the client, in addition to the estimated cost of the soil <br /> vapor extraction alternative, would be incurred for permitting, installing air spargmg <br /> wells, trenching in public right-of-way, bonding cost, and additional operation and <br /> r ' maintenance of the system The cost of this alternative is estimated to be between <br /> y $27500 and $450,000 <br /> o Criterion 5 <br /> This alternative has the potential to remediate subsurface contaminants to acceptable <br /> regulatory levels, however, the time necessary to attain satisfactory clean up levels <br /> roundzcroef.neap <br /> 17 <br />