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' 20 January 2005 <br /> AGE-NC Project No 97-0343 <br />' Page 11 of 21 <br />' 9 1 3 Monitoring Activities <br /> Monitoring of vapor extraction systems involves weekly measurement of vapor concentrations at the <br />' inlet to the destruction unit and periodic service and repair Systems can be equipped with an <br /> automatic telecommunication system to alert the operator of system malfunctton or failure Vapor <br /> samples should be collected monthly for laboratory analysis to monitor the efficiency of the <br />' remediation program When the concentrations of extracted vapor have decreased and stabilized after <br /> a certain period of operation,confirmation borings are drilled to collect soil samples for quantitative <br /> analysis in the laboratory to document the degree of cleanup obtained <br /> 914 Feasibility <br />' Generally,a vacuum of at least 0 10 inches of water is required to successfully volatilize subsurface <br /> hydrocarbons The radius of influence is often considered to be the distance from the extraction well <br />' at which a vacuum of at least 0 1 inches of water is observed (EPA-A guide for Corrective Action <br /> Plan Reviewers) A vapor extraction feasibility test has been performed at the site (discussed in <br /> Section 3 0 ), and the test adequately determined that SVE would be a feasible alternative for soil <br /> remediation There also is a network of three SVE wells (dual completed as SVE and monitoring <br /> wells)already in place at the site,and due to the decrease in the ground water table these wells could <br />' also incorporate dual-zone SVE <br /> One drawback of SVE is that not all contaminated zones of soil are remediated effectively or at the <br /> I same rate For instance, a sandy soil zone will clean up more quickly than a silty one, SVE is not <br /> usually effective in soil with high clay content Other drawbacks of SVE include ineffective <br /> treatment of soil lying below ground water or within the "smear" zone and ineffective treatment of <br />' longer-chain hydrocarbons(I e ,diesel,motor oil) Though,currently soil contamination is all within <br /> the vadose zone at the site <br /> Ground water remediation should be conducted concurrently with SVE to facilitate remediation of <br /> the smear zone <br /> 915 Duration <br /> Cleanup periods for soil vapor extraction typically range from several months to several years Based <br /> upon the plume size and the presence of silt and sand rich soil, an SVE cleanup period of 6 to 12 <br /> Imonths is estimated <br /> • <br /> Advanced GeoEnvironmental,Inc <br />