Water Watch NYC

Everything you need to know about water in NYC.

Tag Archives: Combined Sewer Overflow


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Ten Ways to Save the DEP – #1: Better CSO Notification Procedures

Like most older sewage systems, New York City’s sewage system is what’s known as a “combined sewer system.” This means that the system was never built to accommodate clean rainwater and dirty wastewater separately and therefore, when it rains, the clean rainwater is dumped into the sewer outfalls together with our dirty wastewater.

Sewer Systems

Top: Combined Sewer System. Bottom: Separate Sewer System.

In the image above you can see a perfect example of how NYC’s older sewer system (top)  differs from newer, “separate sewer systems” (bottom). As you see, during dry weather, all that happens in both cases is that wastewater goes to the publicly owned treatment works (POTW). But when it rains, new systems keep the wastewater and rainwater separate and send only the wastewater to the POTW while the clean rainwater goes to the river.

In NYC, when it rains, a mix of rainwater and wastewater goes to both the POTW and to the river. As a result, after heavy rains our sewer outfalls often experience what is called a “combined sewer overflow” or CSO. During a CSO it is dangerous to boat, swim, fish or conduct countless other activities around the heavily polluted water.

The existence of CSOs is in itself a problem that the DEP has to deal with. But it is a problem that will take years and years and billions and billions of dollars. What can we do to mitigate the dangers of CSOs right now?

CSO Outfall Sign

CSO Outfall Sign at Wallabout Bay

The answer is better CSO notification procedures. NYC currently has about 500 CSO outfalls according to the New York Water Environmental Association. In 1999, the city began putting signs up at their CSO sites like this one at Wallabout Bay. The signs say “IF YOU SEE A DISCHARGE DURING DRY WEATHER PLEASE CALL! 311.” Now, I ask you: if you hadn’t read the first three paragraphs of this post, would you know what this means? I wrote the first three paragraphs of this post and I’m still not sure what this means!

Here’s another problem: If it just rained last night and this afternoon your son or daughter wants to go swimming in, say, Paedergat Basin, how are you supposed to know whether or not they are about to climb into a toxic cesspool?

Thanks to pressure from our friends over at SWIM (Storm Water Infrastructure Matters), the DEP (with a little help from HydroQual Environmental Engineers) recently created a web page where you can check on the status of CSO sites around the city. I include a link here so that you can take a look yourself and decide if this is sufficient for a system that has 500 CSO outfalls that your child can be swimming in, that your husband can be fishing in or that the entire family can be taking a boat ride in.

We live in an age obsessed with notifications. The federal government requires notifications on every single pack of cigarettes and bottle of alcohol. The mayor requires calorie counts to be posted in every donut shop in NYC. Why are we more concerned with what we put inside our bodies than with what we put our bodies into? A large, easy to read sign near every single CSO outfall into New York that says something to the effect of “IF YOU SEE WATER COMING OUT OF THIS PIPE, DO NOT SWIM HERE. ALL WATER COMING FROM THIS PIPE IS TOXIC AND DANGEROUS TO YOUR HEALTH” is the best way to keep us safe from the unfortunate, unavoidable effects of CSO.


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Green Roof – Blue Roof

The environmental community is rallying behind efforts to reduce combined sewer overflow (CSO). CSO occurs in New York City when rainfall overwhelms sewage treatment plants resulting in raw sewage being dumped into the adjacent estuary. The city’s solution has been to build huge retention tanks to store the rainfall until the sewage plants can process the load. Unfortunately, retention tanks are extremely costly and the city can not afford to complete construction of the proposed tanks anytime soon.

In response to NYC’s procrastination, the environmental movement has proposed a myriad of best management practices including point of use retention and detention systems. The most popular solution is green roofs. Green roofs are simply roof top gardens that retain rain water to irrigate planting on the roof, hence retaining rainwater on the site. They have the added benefit of eliminating heat island effect, reducing CO2 and literally making the city a greener place. Green roofs are a very elegant solution when intelligently designed and maintained. The drawback is that in cash strapped properties green roofs would be the first system to be neglected. Since environmental realists do not want their solution dependent on building management, they have proposed blue roofs. The concept is quite simple; store rainfall on the roof and slowly allow it to trickle out of the building. In this manner you mitigate the effects of excessive rainfall on the sewage treatment plant.

Recently, many groups have been proposing mandating green and blue roofs. Proponents recommend that all buildings with flat roofs be required to install either a green or blue roof. I wholeheartedly encourage the proliferation of green and blue roofs. However, I oppose any efforts to mandate green or blue roofs. They are just one tool in a plumbing engineer’s toolbox to combat CSO but the toolbox also includes retention tanks, water reuse, irrigation, gray water and a myriad of other design choices. Do we really want to prohibit the installation of rooftop playgrounds and swimming pools? Do we want to find architects specifying sloped roofs solely to exempt a building from green roof requirements? I propose that we require any building applying for sewer permits (SD1&2) to demonstrate that they will retain enough water on site so as to eliminate local CSO occurrences. The DEP should specify retention/detention parameters to accommodate the local infrastructures. Some neighborhoods may not require any retention while other locations with poor sewer infrastructure may have to retain a large percentage of their rainfall. This customized solution might appear to be cumbersome but in reality it is similar to the current procedure used by the DEP to minimize storm water flooding. All the DEP has to do is enhance their requirements for storm water retention. With these requirements in hand, the plumbing engineer can devise an ingenious solution to meet the DEP’s parameters. After careful consideration the engineer might decide on a green roof, blue roof or devise a new solution and term it a yellow roof. The field of study is too new for the city to mandate a specific solution that applies across the board. The DEP should mandate specific requirements and allow the plumbing engineers to do their job.