Dispersion at the field scale resulting from spatial variability of the hydraulic conductivity field

Abstract A two-dimensional mathematical model for simulating the transport and fate of chemicals in aquifers with spatially heterogeneous but isotropic fluid flow properties was developed, as part of an evaluation of bioremediation technologies that include injection of reactants into the aquifer. An important physical process is dispersion of the injected reactant in the aquifer. Dispersion was simulated with the model which has user-prescribed hydraulic pressure fields at the inflow and outflow boundaries. The model accounts for the major physical processes of dispersion and advection and several fundamental chemical and biological processes, including linear equilibrium sorption, irreversible sorption and/or dissolution into an organic phase, microbial degradation, radioactive decay, and other irreversible processes. The chemical may be released internally via distributed leaks from sources that do not perturb the flow field, from fully penetrating injection wells, or it may enter at the inlet boundary. The chemical transport and fate equations are solved in terms of user-stipulated initial and boundary conditions. Simulations were made to evaluate dispersion resulting from spatial variability in the hydraulic conductivity ( K ). Flow fields were divided into regions with hydraulic conductivities of 0.2, 2.0 and 20 m day −1 . Distributions of chemical, initially present as a distributed source near the inflow boundary, were obtained for several geometries of the hydraulic conductivity regions. Results show the influence on distributions of regions of low, medium, and high K ; they demonstrate the importance of knowledge about the hydraulic conductivity field, both for interpretation of sampling data and for prediction of plume behaviour in terms of direction of movement, dispersion and rate of travel.