Throughout most of the United States, wastewater and stormwater flow through separate pipes. Wastewater is directed to a sewage treatment plant, and stormwater flows to local waterways. In a combined sewer system, stormwater and wastewater share the same pipes. During dry or moderately wet weather, the system transports this combined flow to a sewage treatment plant, where it is treated before being discharged into a water body through an outfall. During periods of extreme wet weather, however, the increased volume of stormwater combined with wastewater can overwhelm the system, causing a combined sewer overflow (CSO), during which both stormwater and wastewater flow untreated into local waterways. The resulting pollution can cause waterways to exceed water quality standards and is a threat to public health as well as marine species and habitat. There are currently 21 combined sewer outfalls in New Jersey (USEPA, 1999; USEPA, 2024; NJDEP, 2025).
As urban areas have developed in New Jersey, some streams and rivers may have been rerouted underground through combined sewer systems, which may have increased the volume of water flowing through these systems even during dry weather. During wet weather, this increased volume may in turn increase the frequency of CSOs. One of the main objectives of this project to create a dataset of historical water bodies in New Jersey is to show the location of historical water bodies in relation to combined sewer outfalls so that those that have been rerouted through combined sewer systems may be identified.
The Combined Sewer Overflow (CSO) for New Jersey dataset, produced by the New Jersey Department of Environmental Protection (2023), was used to determine combined sewer outfall locations. If a water body is in the historical water body dataset, but no longer present in that location, and it intersects with a combined sewer outfall, it may have been rerouted through the combined sewer system. If that is the case, returning the historical water body to the surface may reduce the volume of water flowing through the system and the frequency of CSOs for that outfall (Morrison, 2023).
References:
US Environmental Protection Agency (1999). Combined Sewer Overflow Management Fact Sheet: Sewer Separation. https://www3.epa.gov/npdes/pubs/sepa.pdf
US Environmental Protection Agency (2024). Combined Sewer Overflow Basics. https://www.epa.gov/npdes/combined-sewer-overflow-basics
New Jersey Department of Environmental Protection (2025). Combined Sewer Overflow. https://dep.nj.gov/dwq/combined-sewer-overflow/
Bureau of GIS, NJ Department of Environmental Protection (2023). Combined Sewer Overflow (CSO) for New Jersey. https://njogis-newjersey.opendata.arcgis.com/datasets/25bace29e8114519b2d08d04c75873f3_0/about
Morrison, J. (2023, March 15). How ‘Daylighting’ Buried Waterways Is Revitalizing Cities Across America: Urban centers are exhuming creeks and streams once covered up to control floodwater—and bringing life back in the process. Smithsonian Magazine. https://www.smithsonianmag.com/innovation/how-daylighting-buried-waterways-is-revitalizing-cities-across-america-180981793/