The Salisbury Township WWTP in Gap, PA utilized a conventional activated sludge (CAS) system prior to being retrofi tted with an AquaPASS Phased Activated Sludge System in May 2008. The upgrade was necessary in order to comply with the Chesapeake Bay Initiative for local impaired waterways, requiring stringent permit limits on effluent Total Nitrogen and Total Phosphorus by 2010. The plant’s conventional system was not designed for nutrient removal and required only secondary limits of 20 mg/l BOD5, 30 mg/l TSS, 6 mg/l NH3-N, and 2 mg/l TP. Salisbury experienced constant upsets during peak wet weather flow conditions that required operator intervention to prevent solids from rising over the effluent weir. In addition, the conventional system could no longer handle the increased hydraulic loadings from the area’s rapid population growth of about 11.5% in the past nine years.