Combined sewage overflow (CSO) occurs during periods of heavy rainfall when combined sewage and stormwater can surpass a sewer line’s capacity. Normally, sewage is treated before being discharged to a larger body of water. During a storm, where rainwater flows into the sewer, the system is designed to overflow and expel extra discharge straight into the Hudson River and other water bodies. In New York City itself, there are at least 460 CSO outfalls spread throughout the city that discharge more than 27 billion gallons of raw sewage and polluted stormwater into the Hudson River and New York Harbor each year. This doesn’t include the multiple other overflow sites along the Hudson and within New York state. Many other major cities along the Hudson River, including Yonkers, Poughkeepsie, and Newburgh, can have up to 92 outfalls. Although these overflows do fluctuate with the weather, on average, they can occur once a week. All it takes is a tenth of an inch in one hour or 0.4 inches of rain over the course of a day to trigger these overflows. The average weekly polluted discharge is about 500 million gallons Citywide.
CSO’s occur mainly in older cities, due to an outdated sewage system. These cities were designed to hold both sewage and storm runoff in the same pipes, but a possible overflow and safe disposal of excess waste was not accounted for. Less than four percent of municipalities in the United States have combined sewer systems, as newer cities are built with separate systems for sewage and rainfall. For cities with an older system, this can prove to be detrimental to the local waterways. Combined sewage overflows can contain untreated human waste, pesticides, petroleum products, and other potential toxins. Of these toxins, the most significant are pathogenic bacteria and viruses; toxic substances; organic material and nutrients; and debris and other solid matter. There is a high chance of fecal pollution and toxins that can lead to human diseases.
There are multiple solutions that will help lower the overflow within our sewage systems. The best approach is to find better ways to utilize the stormwaters within New York City, rather than see it as a waste that must be disposed of. Stormwater can give life to vegetation which in turn help to offset the effects of climate change, decrease summer temperatures, promote energy efficiency, improve air quality, and make communities more livable
This week, there was a city council joint hearing where NYLCV’s NYC program associate, Carlos Castell Croke, presented testimony on CSO’s. The committee on environmental protection, parks and recreation, and waterfronts and resiliency were also present. The meeting held discussions on possible solutions to tackle this issue and to highlight existing plans. Introduction 1620 was recently passed by the council to ensure that the city develops a plan to stay resilient in the face of climate hazards. The Department of Environmental Protection also implemented the Green Infrastructure Program to directly target CSO’s in accordance with consent orders with the State. The plan is expected to be completed in 2030, but even then, it will not sufficiently prevent CSO’s. Multiple agencies must be involved to build a robust system of resilient green and grey infrastructure in order to protect the city against overflows. The streetscape must be completely reimagined. Castell Croke suggests reprioritizing streets away from cars and toward pedestrian plazas, micro-mobility and public forms of transportation, safe recreational space for New Yorkers, and much more green infrastructure to absorb stormwater, purify the air, and mitigate the urban heat island effect.
Although the Parks Department already maintains over 200 thousand square feet of green roofs across NYC which provide insulation and absorb rainwater, this only covers a fraction of the rooftop space available in the city. The plan is to utilize as many buildings as possible for green roofs to absorb rainwater and reduce sewer overload. As well as expanding the green infrastructure that is already present in our city’s parks and green spaces, careful attention must be placed on the trees and vegetation. New York City parks absorb almost 2 billion gallons of stormwater runoff each year, meaning that they are already a major asset to our city’s resilience. Properly funding and maintaining our parks is a crucial step to ensure that sewage overflows are maintained and properly expelled.