Estimation of effective cleanup radius for soil‐vapor extraction systems

Soil-vapor extraction (SVE) is a standard and effective in situ treatment for the removal of volatile contaminants from vadose-zone soil. The duration of SVE operation required to reach site closure is quite variable, however, ranging up to several years or more. An understanding of the contaminant recovery rate as a function of distance from each vaporextraction well allows SVE systems to be designed so that cleanup goals can be achieved within a specified time frame. A simple one-dimensional model has been developed that provides a rough estimate of the effective cleanup radius (defined as “the maximum distance from a vapor extraction point through which sufficient air is drawn to remove the required fraction of contamination in the desired time”) for SVE systems. Because the model uses analytical rather than numerical methods, it has advantages over more sophisticated, multidimensional models, including simplicity, speed, versatility, and robustness. The contaminant removal rate at a given distance from the vapor-extraction point is assumed to be a function of the local rate of soil-gas flow, the contaminant soil concentration, and the contaminant volatility. Soil-gas flow rate as a function of distance from the vapor-extraction point is estimated from pilot test data by assuming that the infiltration of atmospheric air through the soil surface is related to the vacuum in the soil. Although widely applicable, the model should be used with some caution when the vadose zone is highly stratified or when venting contaminated soil greater than 30 ft below grade. Since 1992, Groundwater Technology, Inc. has been using this model routinely as a design tool for SVE systems.