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,4 <br /> A <br /> Both the effectiveness and the cost of the various alternatives is discussed and a preferred alternative <br /> selected. A pump and treat system is proposed to provide capture of contaminated groundwater. By <br /> lowering the groundwater, the existing soil vapor extraction system can capture exposed contaminants. <br /> Preliminary calculations indicate that at low pumping rates, the capture zone would extend as much as <br /> 1500 feet_ However, the drawdown would only be about 10 feet. This would provide excellent plume <br /> capture but would still require some additional in situ treatment to complete remediation in a timely <br /> fashion . Consequently, we are proposing: <br /> • A pump and treat system with ex sitar treatment of the groundwater, to provide for plume capture <br /> and remediation of groundwater from near the source area; <br /> • Soil vapor extraction to remove those contaminants in the vadose zone exposed by the <br /> groundwater drawdown ; and <br /> • The further remediation of groundwater by enhanced biodegradation and/or chemical oxidation <br /> at injection points within the plume. <br /> The proposed clean-up level for benzene in groundwater is the risk based contaminant level for benzene <br /> at a cancer risk level of one in ten thousand from the ASTM Standard Guide for Risk-Based Corrective <br /> Action. The completed contaminant transport pathways are inhalation of indoor air volatilizing from <br /> groundwater in a commercial setting_ The proposed clean-up level for benzene is 7.3 . 9 µg/L. ,'` We also <br /> propose a default clean-up level for MTBE of the maximum contaminant limit (MCL) of 13 ug/L. <br /> ILA CONDOR <br />