Application of Dual Domain Modeling to Evaluate Remedial Technologies of a Persistent TCE Plume

A solute transport numerical model was developed to estimate the effectiveness of three remedial technologies, enhanced anaerobic bioremediation (EAB), a passive upgradient trench, and a permeable reactive barrier, on a persistent trichloroethene plume.  Previous remedial actions, including phytoremediation and in-situ chemical oxidation, were unsuccessful in effectively treating the plume.  Based on the rebound of concentrations following chemical oxidation and observations from soil borings and an aquifer performance test, the subsurface, which consists of lacustrine clayey silts and a thin fluvial silty/gravelly  sand  layer, was approximated as a dual domain environment.  Two approaches to modeling the dual domain environment were incorporated into the numerical model.  First, the flow model (MODFLOW2000) included a 0.1-ft layer of high hydraulic conductivity between two layers of low conductivity, which was developed based on transient flow modeling of an aquifer performance test.  This model framework represented thin multiple and interconnected fractures in a low permeability matrix.  Second, the solute transport model utilized the dual domain function of MT3DMS.  The mass transfer coefficient was determined through literature review and a sensitivity analysis.  By incorporating both approaches, the model successfully generated concentrations similar in extent and concentration to current observations by simulating from an estimated source date (1956) to present.  The model was used for 50-year predictive simulations to compare the estimated effectiveness of the remedial alternatives.  EAB was the selected technology, and the remedy was implemented. Performance data will be reviewed when available to compare field observations to the model estimates.