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Wet weather events (e.g., rain, snowmelt) can impact publicly owned treatment works (POTWs) operations when excess water enters the wastewater collection system. The increased wet weather flows in the collection system can exceed the POTW treatment plant’s capacity to provide the same type of treatment for all of the incoming wastewater. The treatment plant’s secondary treatment units are the most likely to be adversely affected by wet weather because the biological systems can be damaged when too much water flows through them. POTWs employ a variety of operational practices to ensure the integrity of their secondary treatment units during wet weather, and this update to the regulations will clarify permitting procedures for POTW treatment plant options under wet weather operational conditions. These updates will ensure a consistent national approach for permitting POTWs that provides for efficient treatment plant operation while protecting the public from potential adverse health effects of inadequately treated sewage.