Long Island's drinking water affected by saltwater sinking deeper into aquifer, study shows

Saltwater is increasingly seeping into the aquifer that supplies drinking water to Long Island, a new study has found.

Some drinking wells in western Long Island have been abandoned over the past few decades as they became spoiled with seawater, and the new research suggests that saltwater intrusion is spreading.

The eight-year study, released last Tuesday, is a collaboration between the state Department of Environmental Conservation and the U.S. Geological Survey. It measured chloride (salt) concentrations in dozens of test wells and took seismic surveys and electromagnetic soundings to map the boundary between salt and freshwater in Kings, Queens and Nassau counties.

Phase 2, which will focus on Suffolk County, is expected to be released next year.

The extensive mapping efforts found the saltwater “interface” has moved farther inland than was previously thought in southwestern Nassau, especially in Long Beach and Inwood.

The report makes clear that withdrawals from the aquifer are the cause. “The aquifer system underlying western Long Island has been under stress from pumping of public, irrigation (golf course) and industrial supply wells,” the authors wrote. When large amounts of groundwater are pumped out, saltwater from offshore is drawn in.

Saltwater intrusion from groundwater pumping is nothing new: It has been recorded in Nassau since the 1940s and in Suffolk since the 1970s. This study, which was launched in 2016, found that “a major wedge of saltwater intrusion in the upper glacial-Jameco-Magothy aquifer in southwestern Nassau County appears to be increasing.”

While the DEC said Thursday that the overall water supply on Long Island was not at risk, it also said the saltwater interface shift caused by overpumping is not easily corrected. In some wells, such as in Long Beach, salt concentrations have reached levels that may be irreversible, the study's authors concluded.

Long Islanders use 70% more water each day than the national average, according to Environmental Protection Agency data. Water consumption roughly doubles during the summer, when household lawns and golf courses suck up millions of gallons of water every day. Peak season average daily pumpage for Nassau and Suffolk Counties was approximately 242 million gallons a day and 358 million gallons a day, respectively, according to the USGS.

Experts say that without more stringent conservation measures, saltwater will continue to spread into drinking water wells on Long Island.

The study shows “definitely there are vulnerable areas,” Mindy Germain, Port Washington’s water commissioner and a member of the study's steering committee, told Newsday. The next step, she said, will be for the DEC and USGS to determine how much water can be sustainably withdrawn from the aquifer.

This has to be examined regionally, not just locally, because “withdrawals from the middle of the Island affect the water on the coasts, even though it’s hitting us [on the coasts] first,” Germain said.

Some water districts have made efforts to encourage customers to reduce their consumption through smart irrigation controllers, which prevent lawn watering when the soil is already wet. Starting Jan. 1, Port Washington will require residents to use smart sprinklers.

That’s the “low-hanging fruit,” Germain said — “it’s a 20-50% savings right there.”

The DEC requires public water suppliers to submit water conservation plans and has asked them to work toward a 15% peak season reduction, but there are no mandatory limits. Before the report was made public, the DEC said it would consider pumpage caps if the data warranted it.

The DEC did not say if the findings justify such caps, only that the agency will be reviewing the areas of concern and will work with suppliers to develop plans.