What are Combined Sewers?
Combined sewer systems (CSS) are sewers that are designed to collect storm water runoff, domestic sewage, and industrial wastewater in the same pipe. During rain events, when storm water enters the sewers, the capacity of the sewer system may be exceeded and the excess effluent will be discharged directly to the receiving water. A combined sewer overflow (CSO) is the discharge from a combined sewer system that is caused by snow melt or storm water runoff. Combined sewers are found across New York State (NYS), except on Long Island. However, most CSOs are found in large cities. Most large municipal sewer systems in NYS consist of combined sewers in older downtown urban areas with separate sanitary and storm sewers serving outlying tributary suburban areas.
