More than 27 billion gallons of raw sewage and polluted stormwater discharge out of 460 combined sewage overflows (“CSOs”) into New York Harbor alone each year. Although water quality in New York Harbor and throughout the Hudson River Estuary has improved significantly over the last few decades, many parts of the waterfront and its beaches are still unsafe for recreation after it rains. As little as one-twentieth of an inch of rain can overload the system. The main culprit is outmoded sewer systems, which combines sewage from buildings with dirty stormwater from streets.
This extraordinary degree of pollution imposes steep environmental, human health, and economic costs. CSO discharges, in addition to preventing safe recreation, impair navigation and damage fish habitat.
A legacy of 19th century municipal engineering, CSOs occur mostly in older cities like New York and Albany where the sewage system was designed to collect both wastewater and storm runoff in the same pipes. Less than four percent of U.S. municipalities, 772 out of more than 20,000, have such combined sewer systems. Newer cities are typically designed with separate sewage and stormwater systems.
Wastewater from sinks, tubs and toilets flow from smaller pipes to larger sewer mains, typically three to five feet in diameter. There it combines with runoff from rainstorms as well as all the debris and chemicals that wash off the street or are poured in storm drains.
In dry weather wastewater is transported to a treatment plant, where it is treated before being discharged to a water body. Combined sewage flows to the plants mostly by gravity, but is assisted in spots by pumps.
During periods of heavy rainfall, the combined sewage and stormwater volume can quickly exceed a sewage treatment plant’s capacity. In order to keep sewage from backing up in the system – where it could spurt through manhole covers or backflood into homes and businesses, the combined sewer system is designed to overflow during rains and discharge excess wastewater directly to the Hudson River and other waterbodies.
CSOs contain raw sewage from homes, businesses and industries, as well as stormwater runoff and all the debris and chemicals that wash off the street or are poured in storm drains. This toxic brew can be unappealing and quite dangerous. CSOs contain untreated human waste, oxygen-demanding substances, ammonia, pesticides (such as malathion sprayed on the city to fight West Nile Virus), nutrients, petroleum products (from sources such as gas stations, auto repair shops, and garages), and other potential toxins and pathogenic microorganisms associated with human disease and fecal pollution.
The most significant pollutants in this mix are pathogenic bacteria and viruses; toxic substances; organic material and nutrients; and debris and other solid matter.
Human and animal waste contributes fecal coliform and enterococus bacteria and 40 types of disease-causing pathogens can be are found in raw sewage that discharges in CSOs.
Toxic metals and other hazardous substances come from industrial effluent, street runoff, and from households that contribute paints, oils, solvents and cleaners down the sink drain or storm drains in the street. Pesticides also wash off lawns and gardens into storm sewers.
Debris that washes off the streets or is flushed down toilets includes syringes, tampon applicators, and other plastic products.
For more information on the environmental and human health impacts of sewage discharges, see Swimming In Sewage, a report prepared by NRDC and the Environmental Integrity Project.
For a recent report on the water quality of New York Harbor, see the Hudson River Foundation’s Health of the Harbor (2004). The pathogen section of the report summary stated “The greatest ongoing threat comes from sewer overflows when it rains.”
The frequency and intensity of CSOs fluctuates with the weather. A variety of benchmarks exist for the amount of rainfall required to trigger a CSO. A tenth of an inch of rain in an hour or 0.40 inches of rain over an entire day is the minimum rainfall typically expected to wash pollutants from surfaces and carry them into storm drains.
The average annual rainfall for New York City is about 45 inches. Because 2003 was a particularly wet year, sewage overflowed more frequently than an average year and had greater impacts. For example, in August 2003, beaches were closed and the NYC International Triathlon turned into a duathalon because the water was considered unfit for bathing. In contrast, drought conditions during the summer of 2002 meant fewer closings at those beaches that are impacted by CSOs due to their proximity to outfalls. But sewer overflows are never farther away than the nearest storm cloud.
On average CSO events occur about once per week (and as often as 70 times per year at some outfalls) and the average weekly polluted discharge is about 500 million gallons Citywide.
Source control regards stormwater as a resource to be utilized for much broader sustainability purposes, rather than a waste that must be disposed. By giving life to vegetation, stormwater can help prepare communities offset the effects of climate change, decrease summer temperatures, promote energy efficiency, improve air quality, and make communities more livable.
Source controls may be significantly more cost effective than end-of-pipe controls. Source control systems have been proven effective and are supported by the EPA.
Examples of source control solutions and their benefits if applied in NYC:
• 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.
New York City has at least 460 CSO outfalls that discharge more than 27 billion gallons of raw sewage and polluted stormwater into the Hudson River and New York Harbor each year. In addition, nearly every major municipality on the Hudson River has CSO outfalls, including:
• New Jersey side of NY Harbor: 40+
• New York City: 460
• Yonkers: 26
• Newburgh: 12
• Poughkeepsie: 6
• Kingston: 7
• City of Hudson: 10
• Catskill: 6
• Waterford: 4
• Albany Pool [Albany, Cohoes, Green Island, Rensselaer, Troy, Watervliet]: 92