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Sandy stirs up trouble for city drinking water

Sediment in the water supply could ultimately force city to build costly filtration plant

This story has been corrected.

These are murky times for New York’s drinking water.

Churning seas caused by Hurricane Sandy resulted in a little-publicized increase in the cloudiness of New York City’s drinking water.

Ashokan Reservoir in Ulster County, part of the Catskill-Delaware water system feeding New York City. Photo: Julian Colton/Wikimedia Commons

The condition is known as high turbidity, which is muddiness in H20 created by sediments or other suspended foreign particles.

And, in this case, it was a violation of federal law.

Water-watchers warn that incidents like this could be more common if more events like Sandy hit the New York region — and if they come long and frequently enough, New York City water customers could see federal authorities force them into building a filtration plant that could cost up to $10 billion.

New York City avoids filtration of most of its drinking water only by the grace of the U.S. Environmental Protection Agency, which in 2007 renewed a 10-year waiver allowing water to flow clean from the Catskill-Delaware aqueduct into New York City’s pipes.

But at the time, the EPA flagged muddy water as a looming problem that would eventually require action by the city – either to shore up the system or build a filtration plant.

“Significant improvement to the City’s ability to prevent, manage, and control turbidity in the Catskill system is required in order to maintain filtration avoidance for the long-term,” the agencies wrote.

The New York State Department of Environmental Conservation estimated back then that building such a facility would cost $8 to $10 billion. (One plant is already under construction to filter water originating in the Croton reservoir system east of the Hudson River.)

With climatologists warning that more hurricanes will strike due to climate change, and water advocates saying this increases the vulnerability of reservoirs, New York’s water authorities have begun developing engineering projects and conducting studies to keep the water clear.

“Turbidity is an issue that the city needs to worry about,” said Eric Goldstein, head of the National Resources Defense Council’s New York bureau.

“The system is sensitive, and maybe even extra-sensitive to turbidity from storms,” he said. “It’s a definite warning sign.”

The Catskill-Delaware watershed is an ingenious maze of reservoirs in upstate Westchester County. The reservoir-and-aqueduct system is nearly a century old but continues to serve its original purpose well: transporting 95 percent of the city’s water supply, using gravity only.

But to maintain this system, the city must hold its water to a certain standard.

Under the federal Safe Water Drinking Act, a water system can forgo filtering if it can maintain a near-flawless sanitation record — measured against its ability to keep near-constant turbidity readings below 5 NTU. (NTU stands for nephelometric turbidity units, a measure of the amount of light that can pass through a water sample.)

Last October, after Hurricane Sandy, turbidity spiked to 11 NTU and remained over the legal threshold for 105 minutes, according to the New York City Department of Environmental Protection, which oversees the reservoirs.

In January, the DEP issued a public notice that water samples had exceeded federal turbidity standards.

The notice says that the violation was caused by “large waves…churning up shoreline sediment.”

The statement was being circulated for a first time to customers in Sandy-affected areas after a first batch had been sent along with water bills in other parts of the city in November, according to the DEP.

A spokesman for the agency declined to comment beyond the information contained in the violation notice.

High turbidity also causes disinfecting chemicals used to cleanse drinking water to lose some of their efficiency. That doesn’t necessarily mean harmful bacteria, viruses and parasites will proliferate as a result — but when they do, the resulting cramps, nausea or diarrhea can be damaging to the elderly, infants and those with a weak immune system.

A 1997 study by Harvard University researchers found that hospital emergency room admission levels rose parallel to turbidity levels in an area’s drinking water. The findings are controversial, though, because they have not been replicated.

In its correspondence, the DEP said that the water-sanitation incident did not jeopardize the health of its consumers.

In 2000, the New York City Independent Budget Office forecast that the cost of a filtration plant for the Catskill-Delaware system would trickle down to the average household at a rate of $157 a year by 2018. New York City water authorities have acknowledged that turbidity is “one of the biggest challenges” to the proper functioning of the water system.

Still, the DEP emphasized that the Sandy incident was exceptionally rare.

Two similar violations occurred on March 23, 2006, when levels in the Catskill-Delaware jumped to 19 NTU. And on June 29, 2005, flash floods in the reservoir’s area caused turbidity levels to surge to 20 NTU. The DEP issued public notices disclosing both.

Jonathan Scott, communications director at Clean Water Action, an environmental advocacy group, said that the water system was not designed to withstand the type of violent storms that have begun to hit the U.S. with more frequency.

“The changing climate means more frequent storm events,” Scott said. “That raises questions about how well protected the drinking water reservoirs are from these storms.”

A recent study from Yale University indicates that the current increase in storm intensity, caused by global warming, threatens to increase turbidity levels in watersheds.

In the Catskill-Delaware water system, this phenomenon is compounded by the system’s aging infrastructure, but most of all by the unique geology of the reservoir: easily erodible clay.

When renewing the waiver for avoiding filtration, EPA also criticized the DEP’s reliance on “polluting alum” treatment — a practice that involves dumping aluminum particles into water to capture suspended matter. It requested that it develop a plan to achieve “significant improvement…to prevent, manage and control turbidity in the Catskill system.”

Since that request, DEP reports it has spent or committed to spend around $70 million on planning and research to counteract turbidity caused by large storm events.

An earlier version of this story said that the high levels of turbidity in New York City’s drinking water following Sandy constituted a violation that counted toward a maximum of five such events before the city would have to build a filtration plant. While the matter is being reviewed by the state Department of Health, there is no evidence that the incident constituted such an event.