New York DEP announce revised plans for new hydro plant

10 December 2018

The New York City Department of Environmental Protection (DEP) has unveiled new plans to build a $34 million, 6MW hydroelectric plant at the Cannonsville Reservoir in Delaware County, New York.

The revised proposal follows a 2015 engineering assessment at the site, which found an artesian aquifer downstream of Cannonsville Dam. Initial plans for a 14MW facility, including a 9000ft2 powerhouse, were deemed infeasible after the initial examination of conditions at the site. For more than two years, DEP has worked with experts to study the aquifer and develop a revised plan for generating clean energy at the site.

DCAS is providing $9.8 million for the design and $7 million toward the construction of the plant, which is expected to be complete by 2025.

The proposed hydroelectric plant will include two 3MW generators inside a 4400ft2 powerhouse adjacent to the West Delaware Release Chamber. The turbines will generate an estimated 32,000MWh of electricity each year. The plant will avoid the emission of 23,666 metric tons of carbon dioxide per year. Electricity produced at the plant will be introduced into the grid through a new substation that will be constructed several hundred yards downstream of the dam. The project will create dozens of construction jobs, several full-time jobs to operate the finished plant, and it will generate hundreds of thousands of dollars in new property tax revenue for the Town of Deposit and the Deposit Central School District.

The hydroelectric facility will utilize water that is continuously released downstream of Cannonsville Reservoir. DEP releases water downstream of its three reservoirs on the headwaters of the Delaware River according to provisions of a 1954 US Supreme Court Decree, and an interstate agreement called the Flexible Flow Management Program. The amount of water released from these reservoirs, including Cannonsville, is determined by the season, reservoir storage, hydrologic conditions in the Delaware River, and other factors. DEP will not release additional water from Cannonsville Reservoir to generate electricity; the existing court decisions and agreements will determine how much water goes through the hydroelectric facility each day.

This revised plan for hydroelectric power at Cannonsville Reservoir includes a smaller powerhouse than the original concept that was developed in 2009 and licensed by FERC in 2014. During a 2015 geotechnical assessment to support the foundation design for the larger powerhouse, DEP contractors found that an artesian aquifer – a naturally pressurized pocket of groundwater – was present downstream of Cannonsville Dam. DEP engineers and contractors subsequently performed work to reduce the condition by installing relief wells and used a special grouting technique to shut the boreholes that tapped into the aquifer. The artesian aquifer does not affect the structural integrity of the dam, but its location required DEP to design a smaller hydroelectric facility that will be situated outside the artesian area. The revised plan will draw water into turbines from an available pipe inside the existing West Delaware Release Chamber.

DEP notified officials at FERC that it will no longer pursue the original project. The smaller, revised hydroelectric plant may qualify for a license exemption from FERC because it is less than 10MW.

The proposed facility at Cannonsville Reservoir would be the fifth hydroelectric plant connected to parts of the New York City water supply system in the Catskills. Three of the existing hydroelectric facilities are located in the Town of Neversink in Sullivan County. The Neversink Tunnel Outlet has a capacity of 25MW and generates energy from water as it moves from Neversink Reservoir to Rondout Reservoir. The East Delaware Tunnel Outlet has a capacity of 18MW and generates electricity as water moves from Pepacton Reservoir to Rondout Reservoir. The West Delaware Tunnel Outlet has a capacity of 7.5MW and generates electricity as water moves from Cannonsville Reservoir to Rondout Reservoir. The fourth hydroelectric facility, a 4.75MW plant, is located at Ashokan Reservoir and generates power as water moves into the Catskill Aqueduct. In 2017, those four facilities generated nearly 199 million kilowatt hours of electricity that was sold on the open market by the New York Independent System Operator, which oversees the electric grid throughout the state.

Located on the western edge of Delaware County, Cannonsville Reservoir was formed by damming the West Branch of the Delaware River to store 96 billion gallons of water. Cannonsville Reservoir was the last of New York City’s 19 reservoirs to be built. It was placed into service in 1964. Water drawn from Cannonsville enters the West Delaware Tunnel and travels 44 miles to the upper end of the Rondout Reservoir. From there, it is carried in the 85 mile-long Delaware Aqueduct. Cannonsville Reservoir receives its water from a 455-square-mile drainage basin that includes parts of 17 towns in Delaware County.

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