What a Relief! New Parallel Relief Sewer Helps Reduce Hundreds of Millions of Combined Sewage Discharges into the Bronx River

The lower Bronx River, once a symbol of urban decay, got more relief this summer with a major infrastructure boost. The New York City Department of Environmental Protection completed the installation of a “parallel relief sewer” under Soundview Park that will help eliminate an estimated 237 million gallons of combined sewage and polluted stormwater a year into the river.

The $44.8 million project, which received support from the New York State Water Quality Improvement Project Grant Program as well as from the Long Island Sound Partnership through the federal Infrastructure Investment and Jobs Act, is another milestone in the decades-long effort to clean-up the Bronx River, transforming a highly polluted industrial and litter-strewn waterway into a recreational and ecological resource where local residents canoe and kayak and where migratory fish and other wildlife have returned.  The restoration partners have included federal, state, and local government agencies working with local volunteer and environmental groups.

Close by, in the community of Harding Park in the Bronx, the NYCDEP completed this summer a $24 million project that will trap and prevent “floatables,” large trash items such as plastic bottles, rags, and wood, and other street litter that enter storm drains, from being discharged from an outfall pipe into the East River at the mouth of the Bronx River. The East River connects Long Island Sound with New York Harbor.

According to the Environmental Protection Agency, “Combined Sewage Overflows,” or CSOs, are a major water pollution and public health concern for approximately 700 communities in the United States. CSOs can contain bacteria, debris, and other hazardous substances that can be harmful to people, pets, and wildlife. CSOs can also cause beach closures, shellfish bed closures, algae growth, reduced oxygen levels in waterways, and aesthetic impacts from floating debris or oil slicks. 

The problem impacts cities with older combined sewage and stormwater systems. In dry weather, all wastewater flows to a wastewater treatment plant where it is treated before being discharged to a waterbody. But during wet weather, stormwater also enters the system. The combined flow of wastewater and stormwater can overwhelm the system, and the volume of sewage and stormwater might exceed the capacity of the underground sewer pipe conveying flows to a wastewater treatment plant. Along the Bronx River, this can occur following a heavy rainstorm with a pipe underneath Soundview Park carrying combined sewage to the Hunts Point Wastewater Resource Recovery Facility. If the flow exceeds the pipe’s capacity, some of the combined sewage and stormwater gets diverted to an outfall pipe that discharges the untreated pollution directly into the river.  

The newly constructed parallel relief sewer runs parallel to the existing sewer pipe and will provide more capacity to carry the combined sewage to the plant. Construction of the project began in September 2023 and was certified as complete on July 30.

To support financing for both the CSO and floatable reduction projects, New York City received a $15 million grant from the New York State Water Quality Improvement Project grant program, which is managed by the New York State Department of Environmental Conservation. The Long Island Sound Partnership contributed a $2.4 million share of that grant with funds it received from the Federal Infrastructure Investment and Jobs Act.. The Partnership, through the IIJA funds, has also provided funding support to other NYSDEC grant projects, including two on Long Island – $5.9 million to help upgrade Port Washington’s wastewater treatment system and $1.3 million to support purchase of four acres within Oyster Bay Cove, a designated special groundwater protection area. 

The Bronx projects are being completed through a Consent Order with NYSDEC as part of a federal requirement to attain water quality standards under the federal Clean Water Act. It is a partial step toward meeting standards. The parallel relief sewer is expected to reduce CSOs by 43 percent of the estimated 551 million gallons per year discharged into the river in an average rainfall year. If it is determined water quality standards are not being met, additional projects may be evaluated or alternative water quality standards may be adopted.

According to the NYSDEC, approximately 60 percent of New York City stormwater and wastewater infrastructure uses a combined sewer system, with 398 CSO outfalls that annually discharge approximately 18 billion gallons of combined sewage, making it one of the largest combined sewer systems in the US. Since the 1970s, the City has been implementing projects to reduce combined sewer overflows from its sewer system to improve the water quality of its surrounding waters. In the early 2000s, before the first projects to reduce CSOs discharged into the Bronx River began, an estimated 1 billion gallons of CSOs a year were discharged into the river.

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