To manage a subsurface waste-disposal system effectively it is necessary to predict the response of groundwater systems to various hydrologic stresses. To predict a complex system response generally requires simulation of the field problem through the use of a deterministic model. In the most general case, the complete physical-chemical description of moving groundwater must include chemical reactions in a multicomponent fluid, and requires the simultaneous solution of the differential equations that describe the transport of mass, momentum, and energy in porous media.
The difficulties encountered in solving this set of equations for real problems have forced hydrologists and reservoir engineers to consider simplified subsets of the general problem. The equation of motion for single-component groundwater flow, which describes the rate of propagation of a pressure change in an aquifer, has been solved for many different initial and boundary conditions. To describe the transport of miscible fluids of different density, such as salt water and fresh water, the mass transport equation and the equation of motion have been coupled and solved numerically. Numerical solutions have also been obtained for the heat transport equation and the equation of motion, particularly for convection problems.
A case history of groundwater contamination at Brunswick, Georgia, illustrates the use of the transport equations in predicting the future movement and control of contaminants.
The challenging problem for the future is the simultaneous treatment of mass, momentum, and energy in porous flow and simulation of the complete groundwater system.