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EPA Approves More Stringent Phosphorus Caps for New York City Drinking Water Reservoirs

Release Date: 10/19/2000
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(#00194) New York, New York – Seven of New York City’s most important drinking water reservoirs will be better protected from phosphorus pollution as the result of a U.S. Environmental Protection Agency (EPA) approval of a new phosphorus limit. The new limits are based on a new, more stringent phosphorus guideline set by the New York State Department of Environmental Conservation (DEC), which will protect the most sensitive reservoirs, where the water may be finally collected before being treated and distributed throughout the city. DEC used this new guideline, which applies to seven reservoirs, to set reservoir-specific limits called Total Maximum Daily Loads (TMDLs), which define the maximum amount of a pollutant that a water body can receive and still meet water quality standards. The EPA is today approving these new TMDLs. In this case, the new, more stringent guideline of 15 micrograms of phosphorus per liter was used for the seven reservoirs. In its first phase of setting TMDLs, DEC had used 20 micrograms per liter as the guideline for phosphorus in these reservoirs. DEC will allocate portions of the total load to different sources of phosphorus to control the total amount going into the water. Too much phosphorus can degrade the water, threatening its quality as a drinking water supply. Phosphorus can promote the overgrowth of algae and other aquatic plants. Excessive levels of this organic matter can affect drinking water quality by interfering with disinfection and combining with disinfectants, such as chlorine used by New York City, to form trihalomethanes, which are possible carcinogens. In addition, the organic matter depletes the reservoir of oxygen and leads to conditions that cause non-health related problems with drinking water such as bad taste, odor and color. "These new Total Maximum Daily Loads are more protective of both the health of the reservoirs and the quality of the drinking water that they provide," said Jeanne M. Fox, EPA Region 2 Administrator. "While some reservoirs already meet the new limits, new pollution controls will have to be implemented for others. Some of these controls -- such as upgrades of sewage treatment plants -- are already in the works. EPA will work with the state, the city and other watershed partners to help develop plans for any other needed controls." Of the 19 reservoirs in the two drinking water systems, seven are capable of being terminal reservoirs, the last place water is collected before being treated and distributed throughout the city. For these seven reservoirs, the new phosphorus limit that the water body can take is 15 micrograms per liter, down from 20 micrograms per liter. The water quality limit for the other 12 upstream reservoirs will remain at 20 micrograms per liter. Planned point source controls and further nonpoint source controls will also be needed in many of these reservoirs to meet the 20 microgram per liter limit. Water quality standards are set by states, territories, and tribes. They identify the uses for each water body, for example, drinking water supply, contact recreation (swimming), and aquatic life support (fishing), and the scientific criteria to support that use. A TMDL is the sum of the allowable loads of a single pollutant from all contributing point and nonpoint sources as well as a margin of safety to ensure that the water body can be used for the purposes the state has designated. The calculation must also account for seasonable variation in water quality.