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CLEARWATER <br /> G R O U P I N C <br />' Number of Extraction Wells Required <br /> Once an approximate permeability value has been obtained and is consistent with <br /> known subsurface lithology, the feasibility of reducing hydrocarbon contamination <br /> through vapor extraction in a reasonable period of time (<5 years) can be estimated <br /> using the model presented by P C Johnson, et al (1990) This model is based on the <br /> maximum contaminant vapor concentrations in extracted vapors, residual soil <br /> contaminant composition, vapor pressure, assumed soil temperature and the ideal <br /> gas law and will be determined with the aid of the computer program called <br /> "HyperVentilate®" (Johnson, 1992) The number of vapor extraction wells needed <br /> to remediate the contaminated soil within five years will be determined from the <br /> results of the pilot test and the feasibility calculations and is approximately equal to <br />' the estimated area of contamination divided by the area of influence of one well <br /> All calculations performed in the computer program or performed by hand and any <br /> assumptions used will be presented for review with the data and pilot test results <br /> In addition to estimating the minimum required number of extraction wells using <br /> the radius of influence, the required number of wells will also be determined based <br /> on the required volume of air needed to achieve remediation through <br /> volatilization in a given length of time (TR) This calculation presented by Johnson <br /> & Ettinger (1993) determines the number of wells required (Nw) based on estimated <br /> saturated hydrocarbon vapor concentrations (1/a), an estimated mass of <br /> contaminant to be removed (Mcont), and feasible single well flow rate (Q41e11 - <br /> determined from the step tests) <br /> N = aM T <br /> W ( cont) / (Qwell R) <br />' The two estimates, determined using the radius of influence and using the above- <br /> referenced equation, have inherent limitations and sources of error However, the <br /> results will be compared to estimate a reasonable number of vapor extraction wells <br /> and well spacing Placement of the additional vapor extraction wells, if required, <br /> will depend on the location of existing utilities, buildings, and other site constraints. <br />' Flows and vacuums may need to be modified to ensure complete coverage of the <br /> area to be remediated It must be recognized that the pilot tests and calculations are <br /> performed to provide a basis for the system design The actual system configuration <br /> may be modified from the design based on continual evaluation of operating data <br /> once the system is installed On-going system evaluation will be an important part <br /> of the remedial action <br /> Soil Vapor Extraction Test Protocols Page 4 of 5 December 16,1.994 <br />