Mott MacDonald has helped alleviate the problem of contaminated runoff around Newtown Creek in Brooklyn, one of the most polluted industrial sites in America. In 2013, we were retained to design about 550 bioswales in Brooklyn, the most populous borough in the city with about 2.6 million inhabitants.
For cities served by combined sewer systems, green infrastructure — such as right-of-way bioswales and stormwater green streets — is one way to help prevent sewage from overflowing into waterways when snow or rainfall is heavy.
The basic concept of green infrastructure systems is to divert rainwater runoff that would otherwise enter combined sewers into the ground, where it can infiltrate the soil and be absorbed by vegetation. Impervious surfaces are removed at select locations and replaced with permeable substrate, organic topsoil, and vegetation appropriate to the locale.
Newtown Creek in Brooklyn is a dramatic example of the impact of contaminated runoff on urban waterways. Once a brackish estuary of the Hudson River, Newtown Creek became the oldest continuously used industrial area in the country. With time, the creek was one of the most polluted industrial sites in America.
According to the Newtown Creek Alliance, which is dedicated to restoring the area, the creek has no natural flow because its freshwater sources have been covered over. “Flow exclusively consists of contaminated stormwater runoff, carrying trash from numerous bridges, unsewered and wholly paved streets and industrial sites, waste transfer stations, and combined sewer overflows (CSOs) from the city’s sewer system.”
In an effort to reduce pollution and address the provisions of the Clean Water Act, the New York City Department of Environmental Protection (NYC DEP) began developing its Combined Sewer Overflow Long Term Control Plans. In response to an Amended Consent Order signed with the New York State Department of Conservation, the NYC DEP plans to use bioswales and other green infrastructure to help improve water quality standards.
Bioswales capture rainwater runoff that would otherwise enter combined sewers, allowing it to infiltrate the soil and be absorbed by vegetation. Impervious surfaces, and the soils below them, are replaced with permeable substrate, organic topsoil and vegetation.
The use of bioswales is not always straightforward. Bioswales must be upstream from a catch basin and at least 35 feet from an intersection, and must allow clear access to building entrances and a clear sidewalk path at least eight feet wide.
We gained valuable experience in the use of bioswales and other green infrastructure when preparing design plans and specifications for several green streets projects in Philadelphia.
The client retained us for a project to create right-of-way bioswales in the Newtown Creek CSO tributary area. The project was part of New York City’s Green Infrastructure Program, managed by the NYC DEP in partnership with the city’s Departments of Transportation and Parks & Recreation. We provided:
- Analysis of tributary drainage (approximately 525 acres)
- Site selections
- Geotechnical investigation, including hiring and supervising drillers
- Topographic surveys
- Design of over 550 right-of-way bioswales
- Bidding assistance
The project requires working in a densely-developed urban community with a mix of residential and commercial areas. Coordination with multiple city agencies and concurrent design contracts was required. An aggressive schedule required the design to be completed in under a year. In 2014, we were awarded, by DEP, a new Task Order contract that is expected to include design of several hundred bioswales in the Borough of Queens.
The use Green infrastructure offers New York City a variety of benefits. It helps in:
- Reducing flooding and combined sewer overflows
- Reducing the amount of polluted runoff reaching sewers
- Recharging the groundwater table
- Improving pedestrian and bicycle safety
- Improving air quality
- Alleviating the urban heat island effect
- Making streetscapes more attractive
Newtown Creek is just one example of the potential impact. By reducing the number and quantity of CSOs, green infrastructure will improve water quality in the creek. The planting of trees and other vegetation will improve air quality and make the area more attractive.
Thanks to the efforts of stakeholders, the Newtown Creek Alliance says life is returning to the creek. “You can find blue crabs at the mouth, fish swim in its waters, and waterfowl are prevalent. Wetland plants are taking over the abandoned bulkheads and sediment piles.”