New York City is in the midst of a herculean effort to reduce its combined sewer overflow (CSO) discharges by billions of gallons annually by 2045. But the city does not intend to stop there. As part of a recently released strategic climate plan, New York pledged to essentially eliminate untreated sewer overflows by 2060, an ambitious goal that will require the deployment of green and gray infrastructure on an even grander scale than is already planned.

Before 1990, New York City released more than 100 billion gallons of CSOs annually. By 2022, however, the city had decreased CSO discharges by roughly 85 percent, according to PlaNYC: Getting Sustainability Done. Released by New York City Mayor Eric Adams on April 20, the plan focuses on the city’s efforts to protect its residents from climate threats, improve their quality of life, and build the green economy. Among its goals, the plan aims to address extreme heat and flooding, increase the use of clean and reliable energy, and reduce greenhouse gas emissions associated with buildings, transportation, and food.

PlaNYC “will increase resilience, protect our infrastructure, and save lives,” Adams said in an April 20 news release. “We have so much to be proud of and so much to protect, and PlaNYC will create a cleaner, greener, more just city for all,” he said.

By 2045, New York City expects to reduce its CSOs by more than 4 billion gal/yr, following implementation of 11 ongoing long-term control plans designed to decrease the harmful effects of such discharges. Under the terms of a 2012 agreement entered into with the New York State Department of Environmental Conservation, the New York City Department of Environmental Protection (DEP) agreed to conduct the 11 long-term control plans. Ten of the plans address efforts to achieve water quality standards for individual water bodies, while the 11th concerns the entire city and the open waters around it.

All told, the DEP expects to spend $6.3 billion to implement the 11 long-term control plans, according to PlaNYC. Projects associated with the plans will reduce the release of untreated CSOs by an estimated 2 billion gal/yr and treat and release another 0.5 billion gal/yr of CSOs. 

Examples of such projects include the construction of storage tunnels to capture CSOs that otherwise would enter Flushing Bay and Newton Creek. Expected to cost $3.9 billion, the two tunnels alone will decrease CSOs by 1.4 billion gal/yr. 

In parallel with the long-term control plans, New York will continue to expand its ongoing green infrastructure program. To date, the city has installed approximately 13,000 rain gardens and other green infrastructure assets. Additional efforts will include the installation of 300,000 feet of porous parking lanes in the boroughs of the Bronx and Brooklyn, according to PlaNYC. The DEP also will work with other city agencies “to retrofit impervious surfaces on public properties to capture stormwater at the source,” the plan states.

At the same time, New York City also has mandated that private developers do more to reduce stormwater runoff. In February 2022, the city enacted its Unified Stormwater Rule, which “requires a retention-first approach to on-site stormwater management for all new construction and redevelopment sites” and “sets new thresholds for compliance with post-construction stormwater management practices,” according to PlaNYC. All told, the city estimates that the rule’s requirements will reduce CSOs by about 360 million gal/yr by 2030.

Looking beyond 2045, New York City will develop a “strategy to end the discharge of untreated sewage into the New York Harbor by 2060,” the plan notes. To be crafted during the “next few years,” the integrated strategy will “further [drive] down CSOs and [achieve] applicable water quality standards in the harbor by 2060,” according to the plan. 

That said, the city acknowledges that CSOs may never be eliminated entirely. New York’s “physical space constraints, topography, geology, and feasible funding mean that very extreme storms could continue to overwhelm even the largest investments in the stormwater system,” according to PlaNYC.

The plan also calls for increased efforts to restore and expand wetlands and green spaces in New York. For example, the city intends to plant 30,000 native trees and shrubs across 10 sites to “restore the health of forested areas, which contributes to reduced flooding and higher quality soil, water, and air,” according to PlaNYC. “This effort, combined with maintenance of existing trees and the formation of public-private partnerships to encourage tree planting on private land, will also support our goal to achieve a 30% tree canopy cover and cool our public realm.”