A SIMPLIFIED APPROACH FOR PRELIMINARY DESIGN AND PROCESS PERFORMANCE MODELING OF SOIL VAPOR EXTRACTION SYSTEMS

While soil vapor extraction has been widely utilized as a remedial act ion technology over the past decade, design and associated process per formance modeling of full-scale systems continues to be frequently bas ed on the results of pilot-scale treatability tests. To aid engineers in conducting preliminary scoping studies without the benefit of such treatability data, a relatively simple approach, consisting of linked design and process performance elements, was developed and subsequentl y incorporated into a spreadsheet format for rapid project evaluation purposes. Under this approach, a preliminary design is specified via a set of baseline values which vary based on the predominant soil type encountered at a particular site. Process performance iis then mathema tically modeled by a semi-empirical relation accounting for non-equili brium (mass transfer) effects via use of a lumped parameter, the venti ng efficiency factor (eta) Values for eta vary based on characterizati on of soil heterogeneity. The low values cited for eta (on the order o f 0.02-0.20) reflect the relative inefficiency of field venting operat ions (due to inherent mass transfer limitations) when compared to idea lized conditions. Validation results, considering two case studies rep orted in the literature, indicate that the approach developed provides reasonably accurate predictions. Evaluation of a hypothetical case st udy reveals that the number of extraction vents required as well as th e number of pore volumes of soil vapor that must be extracted for effe ctive remediation can vary by an order of magnitude depending upon the particular soil matrix encountered.