A simplified approach for preliminary design and process performance modeling of soil vapor extraction systems

Abstract

While soil vapor extraction has been widely utilized as a remedial action technology over the past decade, design and associated process performance modeling of full-scale systems continues to be frequently based 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 subsequently 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 is then mathematically modeled by a semi-empirical relation accounting for non-equilibrium (mass transfer) effects via use of a lumped parameter, the venting efficiency factor (η). Values for η vary based on characterization of soil heterogeneity. The low values cited for η (on the order of 0.02–0.20) reflect the relative inefficiency of field venting operations (due to inherent mass transfer limitations) when compared to idealized conditions. Validation results, considering two case studies reported in the literature, indicate that the approach developed provides reasonably accurate predictions. Evaluation of a hypothetical case study reveals that the number of extraction vents required as well as the number of pore volumes of soil vapor that must be extracted for effective remediation can vary by an order of magnitude depending upon the particular soil matrix encountered.