NYC Increases Reservoir Releases to Facilitate Repairs After Their Screw Up

The New York City Department of Environmental Protection (DEP) today increased drinking water diversions and downstream releases from Cannonsville Reservoir to facilitate necessary repairs in response to an ongoing turbid discharge from a rock embankment below Cannonsville Dam.

DEP, its regulators, and consulting experts do not believe, but don't really know if the turbid flow represents any imminent threat to the safety of the dam. While repairs are made, DEP believes it is prudent to draw down the reservoir through increased releases out of an abundance of caution; reducing storage does not pose a risk to the city’s water supply. Except when the river's environmental health is concerned, the NYC believes they can't spare one drop.

The turbid flow below the dam was discovered when workers were drilling borings in preparation for design and construction of the future hydroelectric facility to be built there. During the drilling, workers noticed a flow of turbid water coming from a rock embankment near the release chamber. They immediately contacted DEP engineers and ceased all work.

A preliminary investigation indicated that the drilling released ground water under natural pressure several dozen feet below surface level, causing an upward flow of water and sediment that is reaching the West Branch Delaware River increasing turbidity to that already caused by a poorly managed reservoir.

Since then, DEP has met with its regulators, consulting engineers, and other experts to further investigate the condition, and to identify next steps for monitoring and repair. In addition to reducing storage at Cannonsville Reservoir, DEP is taking several steps to minimize any potential risks. These include 24-hour monitoring by employees at the site, regular analysis of dam-safety instrumentation, and testing of the turbid sediment to identify and understand its origin.

DEP is also working with the Federal Energy Regulatory Commission and the New York State Department of Environmental Conservation on the design and implementation of repairs to stop the flow of water and sediment below Cannonsville Dam.

Federal, state, county and local officials – including officials from New Jersey and Pennsylvania – have been made aware of the condition at Cannonsville Dam. These officials will be updated as DEP continues to examine and address the flow condition. DEP also plans to host a series of public meetings to further inform downstream residents in the days and weeks ahead.  Details on those meetings will follow soon.

Placed into service in 1964, Cannonsville Reservoir was the last of New York City’s 19 reservoirs to be built. Water drawn from Cannonsville enters the West Delaware Tunnel and travels 44 miles to the upper end of Rondout Reservoir. From there, it is carried in the 85-mile-long Delaware Aqueduct. Water is released from Cannonsville Reservoir under the terms of the 1954 U.S. Supreme Court Decree, and a flow program, known as the Flexible Flow Management Program and the NYC OST Program which doesn't work as proven by this seasons flow regime, agreed upon by New York City and the states of Delaware, New Jersey, New York and Pennsylvania. All other reservoirs in the city’s Delaware System will continue to meet their downstream release requirements under the Flexible Flow Management Program while the condition at Cannonsville is investigated and repaired.