Book excerpt: The report develops an approach for reliably evaluating the impact of proposed water pollution abatement plans for a river basin. A water quality simulation model is developed which has the capability of routing acid mine drainage through a river basin. A computer procedure providing for the optimization of alternatives is also developed. The simulation model is used to evaluate alternatives within a larger framework that involves optimization. The approach is to use the simulation as a method of impact assessment which is manipulated by optimization logic. Thus the simulation can be used in two ways: as a stand alone model or as an adjunct to optimization. The Tioga River Basin in Pennsylvania has been chosen as a case study. (Author Modified Abstract).