A system of combined sanitary and storm sewers that directs effluent to a sewage treatment plant during low flows. During rain events excess storm water and sewage is diverted away from the treatment plant to a river or stream. In the late 1940's Minneapolis embarked on a 40year $160 million Combined Sewer Overflow project to guarantee treatment of all sanitary flow and prevent untreated sewage from entering surface waters.
a system of waste removal where storm runoff from streets empties into the same pipes as domestic and industrial wastes. In periods of high rain, the wastewater treatment plant can not handle the increased volume and the wastewater empties through the combined sewer overflows into adjacent waterways without being treated.
A sewer pipe or system through which both sanitary wastewater and stormwater flows. During low frequency storms, both flows remain separate. During higher frequency precipitation events, the stormwater is mixed with the sanitary flow and may bypass wastewater treatment and be released to a receiving water body without treatment.