The Cannonsville Dam, which protects a major New York City drinking water reservoir, is operational again after a construction project struck a pressurized aquifer below the dam.

The incident shines a spotlight on the enormous complexity of the city’s water supply system, and the scores of upstate communities who live in its shadow.

At full capacity, the Cannonsville reservoir holds almost 100 billion gallons of water.

The Department of Environmental Protection, which manages New York City’s water supply and related infrastructure, said in a statement Sunday that the decision to resume normal operations at the dam was made in consultation with federal engineers, and “comes after weeks of testing and around-the-clock monitoring that proved the dam is safe, stable and uncompromised by the cloudy seepage that began three weeks ago.”

In mid-July, initial drilling for a new hydro-electric facility at Cannonsville inadvertently tapped into an underground aquifer. “All drilling work ceased when the workers noticed the flow of turbid [soil-clouded] water coming from a rock embankment near the [dam’s] release chamber,” the City said in its statement.

DEP spokesman Adam Bosch told NYER that testing has confirmed that the water is being released underground about 50 yards below the dam, and that the dam’s integrity was never threatened.

Cannonsville dam
This aerial photo of the worksite below Cannonsville Dam shows the light-colored turbidity that has been coming from the rock embankment and drainage area below the dam. It also shows water being released through the West Delaware Release Chamber, and the drill rig that is digging relief wells to end the turbid discharge by giving the artesian groundwater a new flow path. For more information, visit Photo and text credit: NYC DEP

Bosch said that the hydro-electric project proposed for Cannonsville is now being re-assessed.

The proposed facility, in combination with two other City-run upstate hydro-electric projects, would have the exciting potential to make New York City’s water supply system “energy neutral.” This means that the electricity generated by the three projects would be comparable to the amount of energy required to manage and filter the City’s entire water supply.

Taking steps to protect residents living below the dam

The Cannonsville reservoir and dam are located outside the town of Deposit in western Delaware County. The reservoir holds 95.7 billion gallons at full capacity.

While New York City officials stated that there was no “imminent threat” to the safety of the dam during their investigation, they encouraged local officials, emergency responders and downstream residents to “familiarize themselves” with maps showing areas that would be flooded under a “worst-case-scenario breach.”

In other words, prepare for what would happen if the dam failed when the reservoir was 100 percent full.

And, taking no chances, the City began to drain water from the reservoir into the west branch of the Delaware River as it assessed whether there was any structural threat to the dam. The draining has been stopped and, as of yesterday, the reservoir was at almost 75 percent capacity.

Adam Bosch said that within the week the DEP will seal the construction bore holes that released the pressurized groundwater.

“Intensive monitoring” at Cannonsville will also continue, says the City. This includes 24-hour observations by on-site staff and surveillance cameras, daily engineering inspections, and near real-time monitoring of water quality and safety instruments inside the dam.

Cannonsville: 120 miles away but absolutely essential to NYC

Completed in 1964, the Cannonsville Reservoir was the last of 19 such reservoirs built as part of New York City’s massive drinking water supply system. The City provides more than one billion gallons of water daily to more than 9 million residents, including 70-plus upstate communities in Ulster, Orange, Putnam and Westchester counties.

The watershed area that drains into the Cannonsville Reservoir is 455 square miles, the largest drainage “basin” in the City’s system.

Drinking water from Cannonsville flows into the West Delaware Tunnel and then travels 44 miles to the upper end of the Rondout Reservoir. From there, it is carried in the 85-mile-long Delaware Aqueduct toward New York City.

nyc water supply system
Credit: NYC DEP

A little discussed link to fracking

The Cannonsville dam and reservoir have an interesting connection to the multi-year battle over whether to permit high-volume hydraulic fracturing in New York State.

The reservoir sits on the western edge of Delaware County, within a few miles of the Broome County line. As the debate over fracking raged, New York City officials pointed out that seismic fault lines run throughout the area, posing a potential threat to the City’s water supply infrastructure if they were disturbed.

And while the City was able to preemptively ban fracking within the New York counties that make up its watershed, it had no control over what was going to happen just over the county line in Broome- despite the presence of underground fault lines.

Indeed, Governor Cuomo openly considered allowing fracking in Broome County before the practice was banned statewide. And some local residents leased land to drilling companies for that purpose.

Historic frustration with New York City control

The Cannonsville reservoir was formed when New York City dammed the west branch of the Delaware River. The town of Cannonsville, for which the dam and reservoir are named, was flooded in the process.

west branch map
Map of Delaware County, NY, showing the west and east branches of the Delaware River. Also visible is the proximity of the Cannonsville Reservoir to the Broome County line.

Every day, the New York City DEP releases water from the reservoir into the west branch of the river. Because of concerns about the dam over the last two weeks, the DEP has been releasing three times the normal daily rate of 500 cubic feet of water per second.

City officials say they are now slowly bringing release levels back down to normal levels.

Water is released downstream from Cannonsville under the terms of a 1954 U.S. Supreme Court Decree. A “flow program” was agreed upon by New York City and the states of Delaware, New Jersey, New York and Pennsylvania.

But the City’s daily water releases are at times a source of controversy within communities along the west branch.

west branch of delaware
West branch of the Delaware River. Photo credit:

In a July 31st local TV news segment, some residents of Hancock, which is downstream from Cannonsville, charged that New York City is mis-managing the releases and threatening their local economy.

“We are absolutely done with the way you’ve [New York City] treated us,” said Theresa Allen, a business owner. She charged that cold water releases, especially critical for trout fishing and related tourism activity, dropped by 20 percent in April and May.

“This business, the land it sits on…means nothing if that river is not there and not managed properly,” added Matt Batschelet, who owns a fishing resort on the west branch of the Delaware.

In response, New York City DEP stresses that it has gone to great lengths to work in collaboration with communities that are impacted by the City’s water supply infrastructure and/or constrained by watershed land use regulations.

The City also points to ongoing efforts to support sustainable economic development in its upstate watershed. But Theresa Allen of Hancock notes that besides tourism, “we have no industry in this town anymore.”

What Hancock and other watershed communities do have, however, is proximity to something New York City needs more than anything else- high quality and abundant water.