DC Water's wastewater collection system consists of the following:
- Approximately 1,800 miles of sanitary and combined sewers
- 16 stormwater stations
- 75,000 catch basins and manholes
- 22 flow-metering stations
- 9 wastewater pumping stations
While most of the sewer system contains separate sanitary and storm sewers, combined sewers carrying both sanitary flow and stormwater drainage are prevalent in the downtown area and in older portions of the District. Combined sewer overflows (CSOs) occur during certain storm events when the combined sewer system contains too much flow and the mixture of wastewater and stormwater overflows into local waterways. There are presently 53 CSO outfalls listed in the DC Water’s National Pollutant Discharge Elimination System (NPDES) Permit.
The current CSO Abatement Program combines projects to maximize storage and minimize overflows to receiving waters. The program consists of inflatable dams, dynamically controlled weirs, outfall gates and other flow regulating devices, sewer separations and a swirl treatment facility. The Northeast Boundary Swirl Facility provides preliminary treatment including disinfection and some solids removal for combined sewage overflows prior to discharge during wet weather. The DC Clean Rivers program will further control CSOs.
