Evaluating the predictive capabilities of a three-dimensional simulator (VENT3D) against the performance of a field-scale soil vapor extraction operation
El-Beshry, Manar Zafer
Bedient, Philip B.
Doctor of Philosophy
The design and performance of soil vapor extraction (SVE) systems can be evaluated using mathematical models. A lack of knowledge in how to select the appropriate model and use it properly for field settings are major obstacles limiting the usage of existing codes. The predictive capabilities of many of the commercially available models have never been tested against observed performance of full-scale SVE systems. In this study, we demonstrate the applicability of a coupled, subsurface flow and vapor transport code for simulating the performance of a field-scale soil vapor extraction system. The effects of various modeling simplifications on the accuracy of model predictions, and on the computational time and effort are assessed. VENT3D, a three-dimensional multi-component, multi-phase chemical partitioning model that simulates isothermal flow and transport of organic compounds in the subsurface was selected for testing against data to demonstrate how similar codes can be used to predict the performance of a full-scale SVE system. Simulations were compared to data from pilot- and full-scale operation of an SVE system that was used to remediate a JP-4 jet-fuel contaminated site at Hill Air Force Base, Utah. The standard JP-4 composition was approximated by an equivalent mixture of 11 constituents and as a single constituent using equivalent, mole-fraction-weighted chemical properties, to determine the value of representing mixtures in a multi-component fashion. Air permeability tests data were analyzed independently to estimate vertical and horizontal permeabilities with an analytical model that simulates idealized, axisymmetric gas flow. The initial contaminant mass was the major parameter that had to be adjusted to simulate the contaminant removal using data from pilot and full-scale tests. The value of modeling field studies in a 3-dimensional mode versus 2-dimensional was evaluated. The trade-off between added accuracy in model predictions due to higher problem dimensionality, averaging flow fluctuations, and detailed representation of mixture components, and the extra computational effort and complexity was studied. The model was also used to evaluate the extent of contamination under natural conditions, to predict the effect of long-term operation on cleanup, and to demonstrate how modeling can be used to improve system design and performance.