Combined Sewer Overflows

Annual volume discharged has declined by nearly 30 million gallons per inch of precipitation over the past decade.

Combined Sewer Overflows (CSOs) are discharges of untreated wastewater from municipal sewerage systems that carry mixtures of sanitary sewage, storm water, and sometimes industrial wastes and occur mostly during and after rain events or snowmelt. Currently in Maine there are 30 communities (towns or cities) with CSO discharge points in their sewerage systems (down from an original 60) and all have comprehensive CSO abatement plans. CSOs discharge to receiving waters that vary in size from the ocean and large rivers to small streams and drainage creeks. Water quality is impaired by the addition of floatable solids, bacteria, and sometimes industrial pollutants. Potential shellfishing areas and beaches can be closed and drinking water supplies threatened.

Contact: David Breau (207) 287-7766

CSO annual volume discharged per inch of precipitation

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