A Vapor Extraction Teaching Module Based on AIRFLOW/SVE Primary Researcher: Aaron A. Jennings The AIRFLOW/SVEÊmodule is an example of the kind of instructional modules developed in the NSF/Gateway project. AIRFLOW/SVEÊhelps users evaluates vapor extraction soil remediation. The software also illustrates the use of a true CAD interface to express complex problems and to present results in easily comprehended graphics. Note: AIRFLOW/SVE in a product of Waterloo Hydrologic, Inc,. 180 Columbia St. West - Unit 1104, Waterloo Ontario N2L 3L3, Canada Vapor extraction is one of the fundamental methods of remediating contaminated soil. The process is applied to unsaturated soils in which a significant air flow volume may be induced. The process is typically applied to contaminants that are volatile, but have relatively low water solubilities. Because these contaminants are not soluble in water, they tend to remain trapped in the unsaturated zone. Vapor extraction remediation is accomplished by installing an air well in the unsaturated zone and placing it under vacuum (i.e. pumping air out of the unsaturated zone). The extraction well induces an air flow pattern through the unsaturated zone that can volatilize the trapped organic and remove it from the subsurface. AIRFLOW/SVE models the vapor phase pressure distribution, vapor phase velocity pathways, volatile NAPL concentration profiles, and residual phase NAPL burden profiles around an axisymmetric vapor extraction well. The package operates from a menu-driven environment and CAD user interfaces that help the user create the problem statement and visualize the computed results. The nature of the subsurface partitioning of an organic contaminant is critical to the success of soil vapor extraction remediation. Subsurface organic contamination will generally exist in one of four phases: bulk NAPL, aqueous solution, sorbed solid or vapor. Changes in any of these phases may initiate mass transfers between phases (see Figure at right). If vapor extraction is going to be successful, it must be applied to an organic for which the transfer into the gas phase is strongly favored over other transfers. Vapor extraction can be applied to both ÒresidualÓ contamination and to bulk phase NAPL (non aqueous phase liquids). However, care must be exercised when the contaminant is a bulk phase NAPLs. If there is a large mass of NAPL present, vapor extraction can be like trying to suck an elephant through a straw. When teaching students about vapor extraction remediation, it is very important that they learn both how the method works, and methods to identify when the method works well. The AIRFLOW /SVE instructional module is built around the analysis of a around a single vapor extraction well. The analysis is based on the assumption that the domain is an axi-symmetric (r,z) space extending from the top of the water table (or an impermeable layer) to the ground surface (see Figure at left). The vapor extraction well must be located at the left-hand boundary of the space (i.e. at r=0), but need not be screened over the whole depth of the domain. The right hand boundary (r=R) is taken to be the radius of influence of the well. The bottom boundary is assumed to be impermeable. The top boundary may be a combination of covered ground surface (impermeable) and open round surface (permeable). Covering a portion of the ground surface is a common method of controlling airflow in a remediation application. Either the extraction well potential, or gas volume removal rate may be specified. The soil of the domain may be anisotropic homogeneous, or layered anisotropic nonhomogeneous. Initial conditions may be specified for bulk-phase and/or vapor-phase NAPLs by defining their starting concentrations in rectangular (ri,zi) boxes. The AIRFLOW /SVE instructional module presents a series of sample remediation problems based on this geometry that are designed to help students discover the conditions under which vapor extraction can be a successful remediation alternative. Sources: Jennings, A.A., "A Vapor Extraction Teaching Module Based On AIRFLOW/SVE", Environmental Modelling and Software, (in press), 1998. Jennings, A.A., "Shared Resources Modules to Support Environmental Engineering Education - Vapor Extraction Remediation Based on AIRFLOW/SVE", Final Report, NSF Gateway Coalition grant CID-U-05-CW, Aug., 1996 (209 p). CWRU Department of Civil Engineering Main Menu | Sitemap | Department Activities | On-Campus Menu Communication Click to request a Graduate | Undergraduate Application Form. Click to get in touch with a Graduate | Undergraduate Student. Click to Schedule a Tour of the Department.