The Central Contra Costa Sanitary District is in the process of evaluating the capacity of its activated sludge wastewater treatment plant. Developed in this evaluation was a single graphic, based on a series of assumptions, that combines the capacities of the primary sedimentation tanks, the aeration basins, and the secondary clarifiers. Although a different graphic is necessary for each different set of assumptions, this approach allows the evaluation of the impacts of the performance of each of these process units on the other units. In this manner, the capacity of the whole plant can be realized and advantage taken of excess capacity in one unit that may offset the need to expand capacity in another unit.