Presented are alternative techniques for including conservative solute transport within computer models for optimizing groundwater extraction rates. Unsteady two-dimensional flow and dispersed conservative solute transport are assumed. Comparisons are made of the practicality of including modified forms of implicit and explicit finite difference solute transport equations within optimization models. These equations can be calibrated and subsequently used within a MODCON procedure. The MODCON modelling procedure consists of an integrated series of five optimization or simulation modules. The procedure is applicable for either an entire aquifer system or for a subsystem of a larger system. The first module, A, computes physically feasible recharge rates across the boundaries of the modeled subsystem. Module B computes optimal extraction rates without considering groundwater quality. Module C uses method of characteristics simulation to compute solute transport that would result from implementing the pumping strategy of model B. Module D uses linear goal programming and nonlinear solute transport equations to calibrate linear coefficients. It attempts to duplicate the solute transport predicted by module C. Calibration is performed because coarsely discretized implicit or explicit solute transport equations may not be as accurate as the method of characteristics. Module E includes appropriate calibrated equations of module D as well as the flow equations of module B. It computes an optimal pumping (extraction or recharge) strategy that can satisfy future groundwater contaminant concentration criteria. Testing of the validity of this optimal pumping strategy is subsequently accomplished using module C. If necessary, one may cycle through modules C, D and E until convergence is obtained--until concentrations resulting from implementing the strategy of E are demonstrated to be acceptable
