| Contents Notes |
"A two-dimensional mathematical model for simulating the transport and fate of organic chemicals in a laboratory scale, single layer aquifer Is presented. The aquifer can be nonhomogeneous and anisotropic with respect to fluid flow properties. The physical model for which this mathematical model has been developed Is assumed to have open inlet and outlet ends and to be bounded by Impermeable walls on all sides. The mathematical model allows placement of fully penetrating Injection and/or extraction wells anywhere In the flow field. The Inlet and outlet boundaries have user prescribed hydraulic pressure fields. The steady state hydraulic pressure field Is obtained first, by using the two-dimensional Darcy flow law and the continuity equation. Separate dynamic transport and fate equations are then set up for each of four dissolved chemicals, which Include a substrate, nutrients, oxygen, and nitrate. Two equations, modeling the local growth and decay of two microbial populations, one operating with either oxygen or nitrogen, the other only with oxygen, are coupled to the transport and fate equations. The four chemical transport and fate equations are then solved In terms of user prescribed Initial conditions. Boundary conditions are zero flow at the top, bottom, and sidewalls and accounting of mass at the inlet and exit ports. The model accounts for the major physical processes of dispersion and advectlon, and also can account for linear equilibrium sorptlon, four first order loss processes, including Irreversible chemical reaction and/or dissolution Into the organic phase, and Irreversible binding In the sorbed state. The loss of substrate, nitrate, nutrient, and oxygen Is accounted for by modified Monod kinetic type rate rules. The chemical may be released internally by distributed sources that do not perturb the flow field, or from fully penetrating Injection wells. Chemical compound may also enter at the inlet boundary. Chemical mass balance type inlet and outlet boundary conditions are used. The solution to the field equation for hydraulic pressure Is approximated by the space centered finite difference method using the strongly implicit procedure (SIP) with a user specified heuristic for choosing the Iteration parameter. A solution to the transport and fate equations is approximated with a forward in time Euler-Lagrange time integrator applied to the chemical transport and fate semi-discretization." |
