Last Wednesday evening at CUNY Law School in Queens, the New York City Department of Environmental Protection (DEP) held its annual meeting to discuss Combined Sewer Overflows (CSO) and their Long-Term Control Plan (LTCP) to combat it. New York City is a city surrounded by and reliant upon its waterways, however, the water surrounding the City’s five boroughs is being polluted with massive amounts of sewage leading to high levels of pollution in New York Harbor.
The main culprits of the high levels of pollution in these waterways are New York CSOs and outdated sewer systems, the main topics discussed at the DEP’s Wednesday meeting. Similar to other American cities with aging sewer infrastructure and massive population growth, NYC cannot handle the amount of raw sewage entering the sewers in addition to stormwater runoff which combine and pour into waterways. Every year, 25-30 billion gallons of combined sewage and stormwater flow into the New York Harbor making them unsafe for swimming, boating, fishing, and wildlife. The waste enters the water through 460 CSO outfall pipes (See significant sites on fig. 1, below).
The Federal Clean Water Act, passed by Congress in 1972, mandates that all waters in America be safe for fishing and swimming, making it unlawful to discharge stormwater through municipal separate storm sewer systems (MS4s) into navigable water unless a permit was obtained. In the 45 years since the Act’s implementation, however, NYC has not been able to follow the rules enforced by the Environmental Protection Agency and as a result of its massive population and 50-150 year old sewer system. In a 2008 study done by Riverkeeper, an organization that works to protect the Hudson River Watershed, it was discovered that 32 percent of samples taken from waterways surrounding New York City exceeded the federal single sample guidelines for primary contact. In essence, New York City’s waterways are extremely polluted and not able to be fully enjoyed by the City’s 8.5 million residents.
Because of the unsanitary conditions of NYC’s water, many solutions have been proposed to decrease the CSO contamination since 1990. In 2005, the EPA found NYC in violation of the Clean Water Act and ordered the City to improve water quality by reducing CSO Discharge. As a result of these findings, DEP was tasked to develop a strategy to manage CSOs and was allotted $1.5 billion for public projects and $900 million for private projects to establish the Long-Term Control Plan (LTCP). Spearheaded by a combination of “green” and “grey” technologies, the DEP’s LTCP has made an ultimate goal of managing 1 inch of runoff from 10% of impervious surfaces within combined sewer overflow-served areas of NYC by 2030. Both green and grey Infrastructure have been found to be effective means of mitigating CSO runoff into waterways and are the backbones of DEP’s LTCP.
Green Infrastructure
NYLCV has long supported the implementation of Green Infrastructure throughout New York City. Found to be an effective way to improve the live-ability, health, and appearance of cities, green infrastructure has also been responsible for a significant percentage of the reductions in CSOs over the past few years in New York. Green infrasturcture projects include green roofs, stormwater sewer charges, physical surface detention in the form of rain barrels and or cisterns, bioretention in the form of rain gardens, swales, enhanced tree pits, and green streets, and permeable pavement (see figs. 2, 3, 4 below). A call for city improvement that implements elements of nature comes from the result of a shift from the historical, concrete jungle that New York City has embodied during its 400+ years of rapid urbanization to a modern day green city that is adapted to climate change and its effects.
Green infrastructure will quite literally be groundbreaking for management of stormwater runoff. Already, the DEP has used $410 million for greenf infrastructure in the form of over 4,000 projects around the city. These projects will increase the infiltration rate, detention, and treatment of stormwater and reduce urban runoff while subsequently improving the health of the urban environment. Green infrastructure can also provide coastline resilience, urban heat island mitigation, and reduced energy demand in buildings. These integrated natural areas within urban development will provide habitat for wildlife, protection from floods, as well as improved air and water quality while also providing high visual and ancillary benefits to New Yorkers.
Grey Infrastructure
The remainder of the LTCP has been set aside for grey infrastructure upgrades. Grey infrastructure includes wastewater water treatment plants (WWTP), floatables control, retention tanks, bending weirs, and other sewer modifications that manage flow. Current NYC WWTPs are currently unable to handle flows that are more than twice the design capacity. Flows exceed the capacity of existing grey infrastructure, a mix of excess stormwater and untreated wastewater discharges directly into the city’s waterways at the outfall sites (see fig 1. below).
In general, on a per-gallon basis, grey infrastructure upgrades, new construction, and retrofits have had the largest impact on CSO volume. Existing infrastructure developments have increased the DEP’s standardized CSO capture rate from about 30% in 1980 to over 80% today. In many places affected by CSO runoff, such as areas in the Jamaica Bay Watershed and Coney Island, it was found that grey infrastructure implementation would be more cost effective than green infrastructure.
Storm Resiliency in the DEP’s Long-Term Control
An important and pressing issue facing New York City in addition to CSO is climate adaptation and storm resiliency. At NYLCV we believe it is pertinent that New York City focuses on storm mitigation and climate resiliency while implementing CSO infrastructure throughout the city, both green and grey. If carbon emissions continue to increase at their current rate, sea levels could rise 43 inches by 2080, putting all five boroughs at risk of extreme flooding. Since much of NYC’s sewage infrastructure is outdated, the effects of climate change and future tropical storms could devastate the City and cause greater CSO overflows.
NYLCV believes that widespread green infrastructure will help mitigate storm surge effects by increasing the infiltration rate of floodwaters in coastal areas and because green infrastructure utilizes natural processes to manage stormwater, it has the potential to be more resilient than traditional grey infrastructure. In this way, green infrastructure can be used to build a more resilient city, capable of handling both influxes of sewage and urban runoff and excess stormwater without polluting the surrounding waterways.
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| Figure 1 (source) | Figure 2 (source) |
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| Figure 3 (source) | Figure 4 (source) |