Three-dimensional hybrid modeling of soil vapor extraction

Abstract

Soil vapor extraction (SVE) is being used to decontaminate the north apron area of the former Hong Kong International Airport at Kai Tak. Although SVE is a proven effective in-situ cleanup technology for volatile organic compounds (VOCs), most systems designed to date are based on empirical methods, rules-of-thumb, or results obtained from time-consuming and expensive pilot-scale field tests. Therefore, engineering design tools are definitely needed to extrapolate laboratory results to field applications, to evaluate field test results, to test hypothesis, to evaluate different subsurface scenarios, to optimize operation parameters, to predict field performance and to adjust operation parameters for unanticipated ground conditions. Most existing numerical models use a two-step approach: (1) computation of the negative air pressure distribution induced by the suction applied, followed by (2) simulation of the transport and fate of the contaminant. However, this approach requires a simulation domain considerably larger than the contaminated zone to obtain an accurate air pressure distribution. It is an excessive use of computing resources as only a very small portion of the generated air pressure data will be used for the simulation of contaminant transport. The problem is particularly acute in three-dimensional and multiple-well extraction problems. A three-dimensional hybrid model is thus developed to alleviate these problems in this paper. The model provides the necessary but simple-to-use engineering design tools for the decontamination process. An example application of the model is also presented.