New York City to construct sewage retention tanks for Gowanus Canal cleanup

The City of New York is about to build two Combined Sewer Overflow (CSO) retention tanks to control contaminated solids discharges at the Gowanus Canal Superfund site in Brooklyn, NY.


As ordered by the U.S. Environmental Protection Agency (EPA), the city will construct and operate two CSO retention tanks to control contaminated solids discharges, a key component of the Gowanus Canal cleanup.

The EPA’s order follows previous orders that EPA issued in 2014 and 2016 to require the city to find a location for and design the two tanks. Controls to reduce CSO discharges and prevent other land-based sources of pollution, such as street runoff, from compromising the cleanup are a critical part of the site’s cleanup plan.

“This order will ensure that EPA’s cleanup efforts will not be undermined by uncontrolled combined sewer overflow discharges that have contributed to the chemical contamination of this waterway and impacted this community for the past century and a half,” said EPA Acting Regional Administrator Walter Mugdan. “To ensure the integrity of the dredging work, the retention tanks will control New York City’s sewer outfalls over the long-term.”

The administrative order, issued on March 29, 2021, requires the city to construct one 8-million-gallon tank, located at the head of the canal, and one 4-million-gallon tank, located at a New York City Department of Sanitation Salt Lot near the middle of the canal.

The 2013 cleanup plan for the Gowanus Canal Superfund site includes dredging to remove contaminated sediment from the bottom of the canal, which has accumulated because of industrial activity and CSO discharges.

More than a dozen contaminants, including polycyclic aromatic hydrocarbons, polychlorinated biphenyls, and heavy metals, including mercury, lead, and copper, are present at high levels in the Gowanus Canal sediments.

Dredged sediment that contains high levels of liquid tar will be thermally treated at an off-site facility and disposed. The less contaminated dredged sediment will be processed at an off-site facility to transform it into a beneficial use product, such as landfill cover.

Certain areas of the native sediment, below the original canal bottom, that contain mobile liquid tar and are too deep to excavate, will be mixed with cement and solidified to prevent the migration of the tar into the water of the canal.

Following dredging and solidification of areas of the native sediment, construction of a multilayer cap in dredged areas will isolate and prevent migration of any dissolved chemicals remaining in the deep native sediments.