the state of New York carry this classification. None of the drinking water reservoirs of New York City are Class N.

Each class below N supports fewer uses, and restrictions on discharges into those waterbodies become less strict. Classes AA-S, A-S, AA, and A all support use as a drinking water source, culinary or other food processing source, for recreation, for fishing, and for fish propagation. In addition, Class AA-S waters cannot be polluted with solids, oils, sludges, sewage, and other wastes (which is actually a more stringent requirement than for Class N waters). Class AA-S waters shall also contain no nitrogen or phosphorus in amounts that will result in algal growth, weeds, or slimes (similar to the eutrophication requirement for Class N). The main difference between the three remaining "A" classifications concerns their use as a source of drinking water. Class A-S (international boundary waters) and A waters must be treated with coagulation, sedimentation, filtration, and disinfection (or their equivalents) to qualify as sources of drinking water. Class AA waters require only disinfection. All of the reservoirs in the Catskill/Delaware and Croton watersheds are classified as either A or AA. Classes B, C, and D include waters that can be used for recreation and fishing, but not as a source of drinking water. Waterbodies can be reclassified every three years.

WATER QUALITY CRITERIA

For each use classification, there is a list of physical, chemical, and biological parameters that characterize that classification. These criteria are included in Part 703 of the Water Quality Regulations. The criteria fall under three broad categories: health-based assuming the waterbody is a drinking water source, health-based assuming the waterbody contains consumable fish that might bioaccumulate contaminants, and aquatic-based. aquatic-based. For many chemicals, the criteria are set equal to their MCLs. For oncogenic chemicals, the criteria are based on a one in a million lifetime cancer risk, with does based on a 70-kg adult. Criteria can also be based on former regulations, aesthetic considerations, and chemical correlations. The "Basis for Establishment of Standards" is defined in Table 2, Part 703 of the Water Quality Regulations.

Some of the criteria are narrative; e.g., turbidity in all classes of waters must not increase to cause a substantial visible contrast to natural conditions. There are narrative criteria for nitrogen and phosphorus, stating that for all classes there shall be none in amounts that result in the growth of weeds, algae, and slimes that will impair the waters for their best uses. The 20-µg/L guidance value for total phosphorus that is currently used by NYS DEC appears in a subsequent revision of the Water Quality Regulations.

For almost all other important physical, chemical, and biological parameters, there are specific criteria. Dissolved oxygen, pH, Cl, fecal coliforms, and metals are of most concern for New York City. pH must fall between 6.5 and 8.5 for all



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