ARCHIVED REPORTS XR0000984 - Laserfiche WebLink

Home Browse Search

CLEARWATER G R O U P, I iy C. ' Number of Extraction Wells Required Once an approximate permeability value has been obtained and is consistent with I known subsurface lithology, the feasibility of reducing hydrocarbon contamination through vapor extraction in a reasonable period of time (<5 years) can be estimated using the model presented by P.C. Johnson, et al (1990). This model is based on the I maximum contaminant vapor concentrations in extracted' vapors, residual soil contaminant composition, vapor pressure, assumed soil temperature and the ideal gas law and will be determined with the aid of the computer program called "HyperVentilate®" (Johnson, 1992). The number of vapor extraction wells needed to remediate the contaminated soil within five years will be determined from the results of the pilot test-and the feasibility calculations and is approximately equal to the estimated area of contamination divided by the area of influence of one well. All calculations performed in the computer program or performed by hand and any assumptions used will be presented for review with the data and pilot test results. IIn addition to estimating the minimum required number of extraction wells using the radius of influence, the required number of wells will also be determined based on the required volume of air needed to achieve remediation through PP volatilization in a given length of time (TR). This calculation presented by Johnson & Ettinger (1993) determines the number of wells required (N,) based on estimated saturated hydrocarbon vapor concentrations (1/a), an estimated mass of contaminant to be removed (Mcont), and feasible single well flow rate (Qweli - determined from the step tests): Nw = (a Mcont) / (Qwell TA) ' The two estimates, determined using the radius of influence and using the above- referenced equation, have inherent limitations and sources of error. However, the results will be compared to estimate a reasonable number of vapor extraction wells Iand well spacing. Placement of the additional vapor extraction wells, if required, will depend on the location of existing utilities, buildings, and other site constraints. Flows and vacuums may need to be modified to ensure complete coverage of the Iarea to be remediated. It must be recognized that the pilot tests and calculations are performed to provide a basis for the system design. The actual system configuration may be modified from the design based on continual evaluation of operating data once the system is installed. On-going system evaluation will be an important part of the remedial action. 6 I Soil Vapor Extraction Test Protocols Page 4 of 5 December 16,1994