Dam repairs ahead of schedule: Diversions shift could help conserve cold water

Anne Willard
Posted 12/12/14

GRAHAMSVILLE, NY — Operations to halt the turbid flow below New York City’s Cannonsville Dam are proceeding faster than originally envisioned, according to Adam Bosch, director of public affairs …

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Dam repairs ahead of schedule: Diversions shift could help conserve cold water

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GRAHAMSVILLE, NY — Operations to halt the turbid flow below New York City’s Cannonsville Dam are proceeding faster than originally envisioned, according to Adam Bosch, director of public affairs at the New York City Department of Environmental Protection (NYCDEP). As of Monday, engineers working on the project believed that it might only take three or four relief wells to halt the turbid flow, instead of the eight originally projected, meaning that stage one of the repair plan could be complete as early as sometime this week.

The turbid flow was discovered on July 8 by workers drilling bore holes to take core samples in connection with a projected hydroelectric plant. Subsequent tests have confirmed that the source of the turbidity is these bore holes rather than the dam itself. The relief wells will eliminate turbid seepage into the river by providing an alternative path for the artesian flow that is now traveling through the collapsed bore holes. However, the relief wells are only phase one of the project; repairs will not be complete until the collapsed holes have been sealed off from the surrounding area by a technique called “compaction grouting,” a process that will not be finished until late August at the earliest.

NYCDEP taking steps to address cold water concerns

One of the chief concerns that has been raised by the draining of the reservoir is the potential exhaustion of the supply of cold water below the thermocline, essential to the health of the coldwater fishery in the Delaware River and related recreational industry. Mindful of this, the NYCDEP intends to shift drinking water diversions, which amount to roughly one third of the current total outflow from the dam, from the middle to the top of the reservoir, as soon as the turbid flow is stopped. This should have the effect of slowing the rate at which cold water is depleted.

The NYCDEP put this proposal before the Federal Energy Regulatory Commission (FERC), which has regulatory control over the dam because of the planned hydroelectric plant, early this week, and FERC has given the thumbs up. On Tuesday, August 28, Bosch told us that the NYCDEP expects that the turbid flow will be stopped “sometime this week,” after which they will be able to switch the diversions to the warmer water.

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