One key question for the Napa Sanitation District (NSD) Wastewater Treatment Plant (WWTP) Master Plan Project is the actual WWTP process treatment capacity. Before evaluating the process treatment capacity, the Master Plan team optimized activated sludge operations by implementing an anaerobic selector and alkalinity addition. Once the WWTP operation was stable, the project team collected two weeks of high-quality calibration data for the activated sludge simulator, BioWin. In addition, a secondary clarifier stress test was performed and used to validate the secondary clarifier model, 2DC. The calibrated models were used to determine process treatment capacity under worst-case conditions. Aeration capacity through the aeration panels was determined to limit capacity; the WWTP is currently converting to step-feed operation to maximize capacity. The step-feed configuration provides the added benefit of alkalinity recovery, which will reduce or eliminate the need for alkalinity addition in the future.