Maintaining the Superiority of NYC’s Drinking Water

by Renee Cho | July 29, 2011

New York City is world-renowned for its clean and delicious drinking water. The NYC watershed delivers roughly 1.2 billion gallons of water each day to 8 million NYC residents and 1 million residents of Westchester, Putnam, Orange and Ulster Counties. The watershed’s forests, swamps and soils act as natural filters, removing pollutants, and making NYC’s drinking water supply the largest unfiltered system in the U.S. But in 2013, the Croton Water Filtration Plant, currently under construction in the Bronx, will begin filtering 1.2 million cubic meters or 10% of New York’s water supply each day.

Operated and maintained by the NYC Department of Environmental Protection (DEP), the NYC watershed consists of 19 reservoirs and 3 controlled lakes in a 2,000-square-mile area in the Catskill Mountains and Hudson River Valley, north and northwest of NYC. 95% of the water is conveyed by gravity alone through a remarkable 6,200-mile long system of pipes, tunnels and aqueducts. The Catskill and Delaware watersheds, west of the Hudson River, provide 90% of NYC’s water. The Croton water system, which began operation in 1842, is located east of the Hudson. It supplies 10% of NYC’s drinking water mainly to the Bronx and parts of Manhattan, but is capable of supplying up to 30% in times of drought. So that water can be exchanged among the watersheds in case of local drought or excess precipitation, the three water systems are interconnected.

While NYC’s water is unfiltered, it does get treated with chlorine to kill germs, fluoride to prevent cavities, orthophosphate to inhibit lead contamination from pipes, and sodium hydroxide to lessen acidity. In order for drinking water to remain unfiltered and earn a Filtration Avoidance Determination (FAD), the U.S. Environmental Protection Agency (EPA) requires that a water system not be the source of a waterborne disease, not exceed set limits for coliform bacteria (indicators of fecal contamination and sewage) and turbidity (murkiness caused by suspended solids), and curb levels for trihalomethane (a chemical used in solvents and refrigerants) and disinfectant residues. The system must also implement a program that can minimize microbial contamination of the water, and control local activities to ensure protection of the watershed. To guarantee that NYC water meets these standards, the DEP conducts over 900 daily and 330,000 annual tests on drinking water throughout the city, as well as 230,000 tests in the watershed.

Since the early 1990s, NYC has been granted FADs, allowing water from the Catskill/Delaware system to remain unfiltered. The FAD is contingent upon the DEP providing ultraviolet (UV) radiation disinfection for the water, so a $1.5 billion UV disinfection facility, which will be the world’s largest when it opens in 2012, is currently under construction in Mt. Pleasant, NY.

NYC has been successful in obtaining FADs largely due to the landmark 1997 Watershed Memorandum of Agreement (MOA) negotiated by NYC and New York State agencies, the EPA, upstate communities and environmental groups. The MOA established a watershed protection program that limits activities affecting water quality such as construction, septic system installation, and the building of water treatment plants. It provides for land acquisition, enabling NYC to buy up environmentally sensitive watershed lands from willing sellers and keep them from being developed. And it set up partnership programs with local watershed communities to fund septic system upgrades, repair infrastructure, and deal with agriculture-related and other pollution.

The need to filter water from the Croton system was discussed as far back as 1908, but at the time, chlorination was selected as the best approach to the water quality issues. Although Croton water meets public health standards, it does not always meet the aesthetic standards for water quality. Compared to the other two watersheds, the Croton reservoirs contain more natural organic matter, such as algae, associated with eutrophication, and iron from bottom sediments; at times, these affect the water’s color, odor and taste. Moreover, the Croton watershed is much more populated and developed than the Catskill/Delaware watershed, resulting in more paved surfaces and increased stormwater runoff and pollution. Because of water quality problems, the Croton system went offline for parts of 1992, 1993, 1994 and 1998, and was completely shut down for most of 2000 and 2001.

In 1989, EPA’s new Surface Water Treatment Rule required that all surface drinking water be filtered unless it met tough water quality and disinfection criteria. In addition, the Safe Drinking Water Act mandated all surface water to be filtered by June 1993 unless it could meet strict public health standards. As a result of these more stringent regulations, when the EPA issued the FAD for NYC’s Catskill/Delaware system in 1993, it determined that Croton water would need to be filtered and disinfected because it would be unable to meet all the standards required for filtration avoidance.

Construction on the Croton Water Filtration Plant finally began in 2007 after a complex series of delays caused by lawsuits, changes in agreements and missed deadlines. Following the pullout of the low bidder, Skanska Northeast and the Tully Construction Company were awarded the largest construction contract in New York’s history.

The estimated $2.8 billion project, to be operated by the DEP, will be one of the largest filtration plants in the U.S. The 9-acre, 4-story-deep site is located under the Mosholu Golf Course in Van Cortlandt Park in the Bronx; most of the land will eventually be restored as a golf course. Water arriving from the Croton Reservoir in Westchester County will be filtered for particulate removal; solids will be skimmed off, then dewatered by a centrifuge before being disposed of; the filtered water will be disinfected with UV and chlorine; and after being chemically adjusted, orthophosphate to control corrosion and fluoride will be added. Two huge water tunnels 8,000 feet long that will bring water into the plant and deliver fresh water to the Jerome Park Reservoir distribution system have already been completed. The plant is expected to begin operation in 2013.

The Croton Water Filtration Plant will enhance NYC’s water supply, as it will put an end to Croton shutdowns, add to the flexibility of the overall water system, and improve water quality for New York residents. Maintaining NYC’s high quality drinking water, however, depends on continued protection of the watersheds. According to Riverkeeper, the environmental watchdog organization for the Hudson River and the NYC watershed, NYC has so far spent about $1.5 billion on watershed protection strategies, a good deal that has bought New Yorkers some of the best and least expensive water in the world. But If NYC is unable to safeguard the 90% of its water that comes from the Catskill/Delaware watershed, EPA has the option to require that it too be filtered. Riverkeeper estimates that the cost of filtering the Catskill/Delaware water would be $8 to $12 billion to construct a plant, and $350 million a year to operate it.

Learn more about how to protect the NYC watershed.

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