What is a Combined Sewer Overflow?
A Combined Sewer Overflow (CSO) is a discharge from a combined sewer system (CSS) at a point prior to the POTW treatment plant. CSOs are point sources subject to National Pollutant Discharge Elimination System (NPDES) permit requirements including both technology-based and water quality-based requirements of the Clean Water Act (CWA). How are CSOs Regulated? CSOs are regulated by NPDES permits and the CWA in accordance with the 1994 CSO Policy. The Policy is intended to provide guidance to permittees with CSOs, permitting authorities, state water quality standards authorities, and enforcement authorities. Objectives of the CSO Policy: • To ensure that if CSOs occur, they are only as a result of wet weather • To bring all wet weather CSO discharge points into compliance with the technology-based and water quality-based requirements of the CWA • To minimize water quality, aquatic biota, and human health impacts from CSOs Nine Minimum Controls All NMCs must be continually operated, mainta
Combined Sewer Overflow (CSO) is a discharge of untreated storm and wastewater from a combined sewer into the environment. CSOs typically occur when combined sewers fill up with too much water for the system to handle, most often during heavy rains, and the excess water is released into a stream or river.
