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74 J 14 November 1995 AGE-NC Project No 95-0121 1 Page 9 of 20 Q _ ' concentrations in the vapor stream entering the destruction unit (influent stream) and exiting the system (effluent stream) and periodic service and repair Systems can be equipped with automatic telecommunication system to alert the operator of system malfunction or failure Vapor samples M ' should be collected monthly to monitor the efficiency of the remediation program When the i concentration of extracted vapors decreases and stabilizes after several months of operation,_ confirmatory borings are drilled to collect soil samples for quantitative analysis in the laboratory to ' document the status of the remediation effort ' 614 FEASIBILITY Generally, a vacuum of 0 10 niches of water is,' required to successfully volatilize subsurface hydrocarbons The maximum vacuum measured at EW-1; VW-1 and VW-2 during the pilot test was plotted versus the distance of each well from the extraction well (Figure 4) The effective radius of ' influence (theoretical) is determined by drawing a best-fit line through these data points A clear correlation of induced vacuum verses distance was not observed for this site However, the results of the vapor extraction test indicate that a large radius of influence can be achieved Based upon data obtained during the pilot test, the theoretical radius of influence at the site appears to be approximately 40 feet However, the effective radius of influence is more likely to be 20 to 25 ' feet A strong vacuum will be required to create significant flow rates at flus site A drawback of SVE is that not all contaminated zones of soil are remediated effectively or at the ,Y same rate For instance, a sandy soil will clean-up more quickly than a silt, SVE is not usually effective in sods with high clay content Other drawbacks of SVE include ineffective treatment of soil lying below ground water or within the "smear" zone and'ineffective treatment of longer-chain ; ' hydrocarbons Ground water remediation would need to be conducted concurrently with WE to facilitate remediation of the smear zone M 1 w _ 6 1 5' ESTIMATED COST OF SOIL VAPOR EXTRACTION The costs for vapor extraction systems vanes greatly, depending upon the particular system utilized for destruction of the extracted hydrocarbon vapors (thermal destruction, carbon adsorption, etc) I For the subject site, the cost to operate, maintain, monitor and sample an SVE system will likely= average between,$75,000 to $125,000 per year Rental/lease costs will likely comprise approximately $35,000 to $60,000 per year Maintenance costs can vary significantly, depending upon the specific unit utilized 1 I t ! I I