Source Zone Delineation Demonstration Report - Triad Resource ...

IdealizedStreamlines(Air FlowPathways)IdealizedEquipotential Lines(Negative PressureLines)Figure 5-21. Idealized streamlines and vacuum distribution during SVE operations.Typically, most vacuum dissipation and the highest pressure gradients occur within 15 feet of the vaporextraction well. Thus, SVE designs should be based on pore gas velocities or the rates of pore gasexchange, which, are a function of both the vacuum distribution around the vapor extraction point and theassociated soil air permeability. Ideally, information on spatial variability of radial and vertical gaspermeability should be utilized in support of three-dimensional numerical gas flow modeling. Since gaspermeability is a function of moisture content, spatial variability of gas permeability for any givengeologic environment will be significantly greater than for saturated hydraulic conductivity determinedfor groundwater investigations.Although limitations are associated with using the ROI as the final SVE design basis, the zone ofpneumatic influence does provide the basic information for the initial design of vapor extraction wellspacing. The vacuum distribution measured during the last flow period as a function of distance for eachvapor extraction well during the OU 12 SVE demonstration is shown in Figure 5-22. The data weresubjected to nonlinear regression analyses to obtain an estimate of the zone of pneumatic influence foreach extraction well. Based on a maximum radial extent of induced subsurface vacuum of 0.01 inch ofwater, the zone of pneumatic influence observed during the OU 12 SVE demonstration ranged fromapproximately 50 to 80 feet in the southern section (U12-VP1, U12-VP4, and U12-VP7) of theinvestigative area to over 100 feet in the northern section (U12-VP2, U12-VP3, and U12-VP5). Theaverage zone of pneumatic influence within the investigative area was approximately 85 feet.March 2003 5-32 OU 12 Demonstration ReportFinal