The Harlem River Plant Fire and New York City’s 150 Year Old Sewer Problem
Last week, a fire in the engine room of the North River Wastewater Treatment Plant — located on the Hudson River, from 137th Street to 145th Street — shut the plant down, causing millions gallons of untreated sewage to pour into the New York waterways. The North River plant is one of the largest in New York, handling all the waste from the West Side of Manhattan above Greenwich Village. According to the New York Times, about 120 million gallons a day is treated there, but it can handle up to 340 million gallons when it rains.
Here is a great video from DEP about how the wastewater treatment process works at the North River Plant. The plant utilizes gravity to bring sewage to the plant: wastewater runs downhill to the plant from the higher elevations of Washington Heights and Inwood. An artificial slope is created to bring the wastewater up from Lower Manhattan: “a sewer line about six inches below the street at Bank Street gradually drops to a depth of 50 feet by the time it reaches the Upper West Side.” Once it gets to the plant, the wastewater is pumped five stories up by engines like the one that caught fire last week. As the sewage slowly descends, “it goes through aeration and settling tanks, as well as a biological process that digests much of the waste”.
When the fire shut down the North River plant, the city temporarily returned to dealing with Manhattan’s West Side sewage as it had prior to the Clean Water Act in 1972: dumping it directly into the Hudson River and Harlem Rivers. Here is a list of the 56 outfall locations, through which the waste water rushed out into the rivers. The sight of raw sewage in the water on Friday made me appreciate the 14 sewage treatment plants that were built with federal funds after 1972.
While the infrastructural improvements precipitated by the Clean Water Act have significantly improved the quality of our waters, New York City, like many other older urban areas, has a combined sewer system. This sewer system is a result of 19th Century engineering, which could not have foreseen modern rates of water usage. The system does not separate clean rainwater from dirty wastewater. During heavy rains, when a lot of rainwater enters the sewers, the capacity of the sewer system becomes exceeded. The excess water is discharged directly into the rivers, similarly to what happened last week when the North River plant was out of commission. Even though the amount of wastewater dumped into the water— 360 million gallons— is horrifying to think about, the Combine Sewer Overflow (CSO) sends a similar amount of wastewater into the water after a few days of very heavy rainfall.
Now that the plant is running again – thanks to one hundred people working overtime on an extremely hot day – the raw sewage will decapitate in a few days, making the waters safe for usage. As far as long term solutions to the CSO problem, the most sustainable options are those that decrease the amount of water that enters the sewer system (source-control), rather than “end of pipe” controls, which attempt to deal with the wastewater after it enters the system (large holding tanks, for instance). Here are some figures from Riverkeeper about green solutions to the CSO problem:
• Greenstreets could decrease CSOs by 14,800 gallons
• Street trees could decrease CSOs by 13,170 gallons
• New green roofs could decrease CSOs by 810 gallons; retrofitted green roofs could decrease CSOs by 865 gallons; and incentivized green roofs could decrease CSOs by 12,000 gallons
• Rain barrels could decrease CSOs by 9,000 gallons.
Images courtesy of Gotham Gazette, New York Times and Wikipedia