Development of Design Tools for In Situ Remediation Technologies

Tools were developed to assist in the design of groundwater remediation systems by in situ chemical oxidation with permanganate (MnO 4-) and in situ bioremediation with soluble substrates (SS). These tools can be used by remediation system designers in developing more effective systems for distributing amendments to enhance contaminant degradation.;Permanganate distribution following injection for in situ chemical oxidation is often controlled by the natural oxidant demand (NOD) of the aquifer solids. Six different models of MnO4- consumption by NOD were fit to NOD test data from 50 samples of aquifer material. Representing oxidant consumption as an initial instantaneous reaction with a portion of total NOD and as a slow second order reaction between MnO4 - and remainder of total NOD provided a good match with experimental results without an unnecessary computational burden. Wide variations in total NOD, fraction fast/instantaneous, and second order rate coefficients were observed. Most of the NOD present was slow reacting; MnO4 - could persist for weeks to months. The 48-hr NOD measurements were poor predictors of total NOD and should not be used to estimate total MnO 4 consumption. Total NOD was not correlated with the fraction of fast/instantaneous NOD or the reaction rate coefficients, indicating the total amount of NOD is not a good predictor of reactivity.;The impact of aquifer characteristics and injection system design on aquifer volume contact efficiency (EV) and contaminant mass treatment efficiency (EM) following MnO4- injection were evaluated. MnO4- consumption was simulated assuming the contaminant and the fraction of NOD react instantaneously and rest of NOD reacts slowly with second order relationship. The mass of permanganate and volume of water injected has the greatest impact on EV. Several small injection events are not expected to increase EV compared to a single large injection. High groundwater velocities, low NOD reaction rate, and low total NOD can increase the EV and the fraction of unreacted MnO4-.;A spreadsheet–based design tool (CDISCO) was developed to simulate the distribution of MnO4- in aquifers. The user enters the aquifer conditions, injection parameters, unit costs for labor and materials, and design parameters. Modeling results of MnO4 - transport are used to estimate the radius of influence (ROI) and well spacing. CDISCO then provides a preliminary cost estimate for the selected design conditions; and user can perform CDISCO repeatedly to have optimum design. Comparisons with analytical and numerical models demonstrate that CDISCO accurately simulates MnO4- transport and consumption. Comparison of CDISCO results with the three-dimensional heterogeneous simulations show that EV and EM are closely correlated with the ROI overlap factor.;The effectiveness of different approaches for distributing soluble substrate (SS) to enhance in situ anaerobic bioremediation was evaluated in a series of numerical simulations where SS consumption by microorganism was represented by the standard form of the advection-dispersion equation with a first order decay term. Contaminant biodegradation was assumed to be effective if the SS concentration at a location was greater than a user specified value. The impact of SS injection (CI) and target (CMIN) concentration, travel time between rows of wells (TT), SS half-life (TH), reinjection interval (TR) and injection pore volume (PV) on steady-state contact efficiency (CESS) were investigated. In general, CE SS is highest when TR is low, PV is high, and CI/C MIN is high. A tool for designing ISB using SS was developed. Users enter information on (1) aquifer characteristics, (2) well, injection, and substrate, (3) treatment zone dimensions, and (4) design parameters to estimate the system performance. Users can then compare alternatives to identify designs with the highest ratio of CESS to total costs. Generally, the highest ratio occurs in the range of 70%∼80% of CESS.