On September 28, 2010, the City released the NYC Green Infrastructure Plan, which set forth a series of initiatives and opportunities to dramatically change the way we manage stormwater. New York City, like other older urban centers, is largely serviced by a combined sewer system where stormwater and wastewater are carried through a single pipe. Even though treatment plants are designed to treat and disinfect twice the dry weather flow, during heavy storms the conveyance system can exceed its capacity and is designed to discharge a mix of stormwater and wastewater—called combined sewer overflow or CSO—into New York Harbor in order to prevent treatment plants from becoming compromised.

What is it?

Drivers of Action 

PlaNYC, Mayor Bloomberg’s sustainability plan published in 2007, committed the City to build more Bluebelts and Greenstreets, require green parking lots, incentivize green roofs, and form an Interagency Best Management Practices Task Force. The Sustainable Stormwater Management Plan issued by that task force concluded that green infrastructure was feasible in many areas in the city and could be more cost-effective than certain large infrastructure projects such as CSO tunnels in terms of stormwater retained or detained. The NYC Green Infrastructure Plan built upon these analyses by modelling CSO reductions associated with both green and grey infrastructure, and extended, the commitments made in PlaNYC and the Sustainable Stormwater Management Plan to meet the twin goals of improved water quality in New York Harbor and a more liveable and sustainable New York City.

Planning and Implementation

NYC like other municipalities is subject to U.S. federal laws including the Clean Water Act, which mandates reductions in contamination of the city’s waterways. Conventionally this regulation would mandate expensive engineered infrastructure of sewer pipes and treatment facilities. By proposing and documenting the effectiveness of a green infrastructure approach to supplement (not replace) the conventional approach NYC was deemed to have met the regulatory requirement through a new path to compliance. On March 13, 2012, the City and the New York State Department of Environmental Conservation (DEC) finalized an historic agreement that incorporates an iterative, adaptive management approach, committing the City to the goals set forth in the NYC Green Infrastructure Plan. In exchange, DEC eliminated approximately $1.4 billion in grey infrastructure projects, and agreed to defer another $2 billion in additional grey infrastructure that had been proposed, providing the City with the necessary time to build and monitor green infrastructure projects.

Sustainable Initiatives

The NYC Green Infrastructure Plan has five key components:

  1. Build cost-effective grey infrastructure — The City will construct $2.9 billion of cost-effective grey infrastructure investments by 2030, including CSO detention facilities, upgrades to wastewater treatment plants, and high level storm sewers. To date, the City has constructed three CSO detention facilities and finalized designs to maximize wet weather flow at one of our wastewater treatment plants.
  2. Optimize the existing wastewater system — The City will optimize the existing system by ramping up sewer cleaning, inspecting and repairing all 550 tide gates, and encouraging our customers to reduce their consumption through real-time Automated Meter Reading (AMR) data, a Leak Notification Program, and conservation education. The City has inspected all of the interceptor sewers, begun tide gate repairs, installed more than 800,000 AMR devices, and launched a Leak Notification Program. 
  3. Control runoff from 10% of impervious surfaces through green infrastructure — The City will control runoff from 10% of impervious surfaces through the construction of green infrastructure, such as bioswales, blue and green roofs, and rain gardens, on public property and in the right of way. The City has implemented new standards that incorporate stormwater management techniques in new building designs, instituted a stormwater charge for parking lots that drain into a combined sewer, and built green infrastructure pilots throughout the city. 
  4. Institutionalize adaptive management, model impacts, measure CSOs, and monitor water quality — The City will institutionalize adaptive management, improve our water quality modelling, measure program performance and actual CSO discharges, and monitor ambient water quality to ensure that the plan achieves not only CSO benefits, but overall water quality improvements as well. In addition to signing the consent order with DEC in March, the City has added an additional 12 water quality sampling stations throughout the harbor.
  5. Engage and enlist stakeholders — The City will actively solicit comments and suggestions through the Green Infrastructure Citizen’s Group and the Steering Committee, and present opportunities for stakeholders to engage through stewardship programs and online educational resources. To date, the City has held two citizen’s group meetings and four Steering Committee meetings.

Economic and Environmental Impacts

Together with conservation measures and operational improvements, the widespread adoption of green infrastructure can reduce more CSOs at less cost than second-tier “grey” infrastructure. Moreover, green infrastructure projects provide many quality of life benefits by improving air quality, increasing shading, increasing property values, and improving our streetscape.

The significant sustainability benefits of this plan will begin to accrue immediately and build over time, in contrast to tanks, tunnels, and expansions, which provide only water quality benefits at the end of a decades-long design and construction period. Over the next 20 years, the City projects that the NYC Green Infrastructure Plan will reduce CSO volumes from approximately 30 billion gallons a year to approximately 18 billion gallons per year. This is nearly 2 billion gallons per day lower CSO volume than would be achieved by a wholly grey strategy. By 2030, we estimate that New Yorkers will receive between $139 million and $418 million in additional benefits such as reduced energy bills, increased property values, and improved health.

Barriers and Solutions

New York City is one of the densest and most urbanized cities in the world, and many technologies that work in other areas are not well-suited for our ultra-urban environment. The NYC Green Infrastructure Plan adopts an adaptive management approach, which builds in trial and error as we learn which technologies are most cost-effective in the City. We also realized that upgrades to public property alone will not achieve the water quality improvements that New Yorkers deserve. In 2011, the City awarded more than $3.8 million through the Green Infrastructure Grant program, which provides funding for stormwater management projects on private land in priority combined sewer watersheds. On January 4, 2012, DEP promulgated a new stormwater performance standard to modify the flow rate of stormwater to the city’s combined sewer system from new and expanded developments while providing flexibility for applicants to comply with stricter release rate requirements based on the availability of different technologies and site specific conditions.

Next Steps

The City has already completed construction on three CSO detention facilities, ten bioswales, and a number of other green infrastructure pilots on City property. In 2012 the City will invest millions of dollars to construct more than 60 green infrastructure installations and award $5 million in green infrastructure grants. DEP will also continue to collect and analyze monitoring data across 25 green infrastructure pilots already constructed.


Carter H. Strickland, Commissioner
NYC Department of Environmental Protection
59-17 Junction Boulevard
Flushing, NY 11373
(718) 595 – 6600