An Analysis of Density Enhanced Remediation of DNAPLs

The contamination of groundwater by dense non-aqueous phase liquids (DNAPLs) poses one of the most pervasive and difficult groundwater remediation problems in the field of environmental engineering. A new concept, density enhanced remediation of DNAPL(DERD), has been proposed by Dr. Cass T. Miller that relies upon mobilization of a DNAPL while controlling its vertical migration. This report presents a conceptual model for the implementation of DERD and an analysis of the effects of selected decision variables on DERD process efficiency. Computer simulations were performed that modeled 1) injection of a dense brine into the subsurface to form a barrier against vertical DNAPL migration, and 2) subsequent extraction of the injected brine through production well(s). Dimensionless parameters formed from decision variables and hydrogeological characteristics were used to analyze simulation results, and an objective function, based on capital and recovery costs for the brine, was calculated for each simulation to rank decision variable strategies. The computer code used for this study (HST3D, developed by the U.S. Geological Survey) employs finite difference methods to solve three-dimensional groundwater flow, heat, and solute transport in a saturated porous medium. Analysis of the results revealed an optimal range of production and injection rates for each specified well spacing configuration that minimized the unit cost objective function. In addition, the objective function was minimized by injection to production rate ratios near 1.0 and by use of variable pumping rates for both the injection and production wells. Brine recovery efficiency was improved by extraction through multiple wells rather than the central well alone. High permeability and low permeability homogeneous medium simulations resulted in similar unit costs and quantities of brine, but the timescales required to complete the process were significantly longer for low permeability soil. Segmentation of the simulation domain into strata with different soil permeability resulted in less efficient brine injection and higher brine unit costs.Master of Science in Environmental Engineerin