Three-Dimensional Soil Venting Model and Its Applications

Abstract

In-situ soil venting has emerged as a promising remedial technology for soils contaminated with volatile or semi-volatile organics. A three-dimensional numerical model is developed to predict subsurface air pressure and velocity profiles during soil venting. The applications of the model include estimating the zone of influence, air flow rate, and pressure drawdown induced by a venting system. Estimated values of these parameters are needed for system design. The paper provides practical examples of how to use the model. These examples show the effects of air supply wells and injection wells on the zone of influence.Soil contamination by volatile or semi-volatile organics from leaky underground storage tanks has recently been recognized as a major environmental problem. Insitu soil venting, also known as vapor stripping or vacuum extraction, has emerged as a broadly accepted remediation technique for this problem. The technique uses vacuum pump(s) to pull air from contaminated soil zones through a network of vapor extraction wells. The induced air flow sweeps the pore space and disrupts the equilibrium among the contaminants in the moisture phase, in the soil vapor phase, and on the soil surface. The process enhances volatilization of the contaminants into the air stream from both the soil surface and the moisture phase. It also replenishes oxygen within the contaminated zone and may accelerate biodégradation of contaminants by indigenous microorganisms.The available literature indicates that studies of the venting technique for remediation of contaminated soils started in the early 1980's. Thornton and Wootan presented the results of an experimental study, sponsored by American Petroleum Institute, in 1982 (1). Since then, the literature has reported quite a few controlled experimental studies and field venting operations (2-6, 15, 18-20). However, the reported information is somewhat limited (7) and the design of vacuum extraction in these field operations was done by empirical and site-specific approaches (8). Therefore, there are few guidelines available in the literature for the optimal design, installation and operation of soil vapor extraction systems (20).

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

“…The A/A-D equation method is commonly taken; a review of literature-reported SVE models (Table 1) yielded twenty-two coupled air flow/contaminant transport and removal models [ 7-28], as well as six air flow-only models [29][30][31][32][33][34] based on this approach.…”