Retrofitting Publicly-Owned Treatment Works for Compliance is intended as a source document for individuals responsible for improving the performance of an existing, non-complying wastewater treatment facility. Described are: 1) methods to evaluate an existing facility's capability to achieve improved performance, 2) a process for systematically improving its performance, and 3) details on how to modify the facility to achieve the required levels of performance. The manual emphasizes meeting National Pollutant Discharge Elimination System (NPDES) permit requirements for secondary treatment facilities (30 mg/L BODs and TSS).