The imposition of recent U.S. legislative requirements (Public Law (PL) 92–500) with the 1977 and 1983–1985 water quality goals requires that water quality management plans must weigh both degree of treatment and capacity expansion questions. A planning model capable of reflecting the implications of the pollutant constraints and the scale economies of point source abatement implicit in the legislation is developed. The model captures within a mathematical programing format important characteristics of decisions associated with the time‐related water pollution control goals of PL 92–500. The model's unique features are the utilization of a biomass potential parameter as a measure of water quality and a set of heuristic procedures involving linearization of the waste treatment capacity‐removal curves. These features allow avoidance of nonconvexity problems associated with analogous models. The model also includes the usual BOD, DO, N, and P water quality measures. The model was applied in a recent planning study for the Saint John Basin