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Ashokan Reservoir

Ashokan Reservoir with mountains in the background

Available for Public Review and Comment: Draft Environmental Impact Statement (DEIS) for the Modification of the CATALUM SPDES Permit, and Draft Permit

A virtual legislative public comment hearing was held March 3, 2021 and information can be found in the New York City Department of Environmental Protection (Catalum) hearing notice.

DEC, as lead agency, has released for public review and comment the Draft Environmental Impact Statement (DEIS) evaluating the proposed modification to the NYSDEC State Pollutant Discharge Elimination System (SPDES) Permit for the Catskill Influent Chamber (Catalum SPDES Permit No. 026 4652). The public comment period for the submission of comments on the DEIS was extended until June 16, 2021.

The Draft Environmental Impact Statement (DEIS) evaluates the potential for significant adverse environmental impacts to occur from implementation of the turbidity control measures proposed to be incorporated into the Catalum SPDES Permit (Turbidity Control Measures), as well as from the postponement of dredging in the Kensico Reservoir until the completion of specific infrastructure projects. Implementation of the turbidity control measures analyzed in this DEIS would allow NYCDEP to continue to provide reliable, clean, and safe drinking water while reducing reliance on chemical treatment of the water supply, specifically the use of alum, during episodic turbidity events.

The permit modification proposes turbidity control measures, including operation of the Ashokan Reservoir in accordance with a revised Ashokan Reservoir Release Protocol.

Please see the List of Studies, Reports, EISs Obtained and Considered in Preparing the modification of the CATALUM SPDES Permit DEIS (PDF).

The draft documents that are available for review and public comment include:
Modification of the CATALUM SPDES Permit Draft Environmental Impact Statement (DEIS)

The documents are also available (leaves DEC website) at the NYCDEP's website. Contact: Kristen Cady-Poulin, NYSDEC, Division of Environmental Permits, 625 Broadway, 4th Floor, Albany, NY 12233-1750, Phone: (518) 402-9167, E-mail: or

Agreement to Manage Turbidity

Construction for Ashokan Reservoir. View of Olive Bridge dam showing down-stream face of masonry section. Stone crusher and concrete mixing plant in left background. June 21, 1910.
Construction for Ashokan Reservoir. View of Olive Bridge dam
showing down-stream face of masonry section. Stone crusher
and concrete mixing plant in left background. June 21, 1910.

DEC and the New York City Department of Environmental Protection (NYCDEP) have agreed on an to manage turbidity and manage reservoir releases. This will improve water supply, water quality and habitat, and provide flood mitigation in the New York City watershed. The terms of the consent order also decrease the need for aluminum sulfate to be used in the Catskill Water Supply System.


Information About the Ashokan Reservoir

From New York City's Department of Environmental Protection: Located in Ulster County, about 13 miles west of Kingston and 73 miles north of New York City. Formed by the damming of the Esopus Creek. Consisting of two basins separated by a concrete dividing weir and roadway, it holds 122.9 billion gallons at full capacity and was placed into service in 1915. It is over 190 feet deep at its deepest point.

The Ashokan is one of two reservoirs in the City's Catskill Water Supply System. The other is the Schoharie, located 27 miles to the north, whose water flows into the Ashokan via the Shandaken Tunnel and the Esopus Creek. Including the water it receives from the Schoharie Reservoir, the Ashokan supplies about 40% of New York City's daily drinking water needs in non-drought periods. Water enters the Ashokan's West Basin and, after a settling period, is withdrawn from its East Basin. It is carried southeast under the Hudson River via the 92-mile Catskill Aqueduct, which has a maximum depth of 1,114 feet. It ordinarily enters the Kensico Reservoir in Westchester for further settling, where it mixes with Delaware system water and then travels south in two aqueducts before entering New York City's water supply distribution at the Hillview Reservoir in Yonkers, just north of the City line.

The Ashokan watershed's drainage basin is 255 miles and includes parts of 11 towns: Denning, Hardenburgh, Hurley, Kingston, Marbletown, Olive, Shandaken and Woodstock in Ulster County; Hunter and Lexington in Greene County, and Middletown in Delaware County.