Combined Sewer Overflow

When households dispose of wastewater from toilets, sinks, clothes washers, and dishwashers, it travels through underground pipes to a Wastewater Treatment Plant (WWTP). The WWTP treats the wastewater to State standards before discharging it to a local stream or river. In some cities, however, older sewer systems were designed to also accept stormwater runoff from the city during rain events. A Combined Sewer System (CSS) is then a system of pipes that carry both wastewater as well as stormwater during rain events.