As a new study shows, salt water is increasingly seeping into the aquifer that supplies Long Island with drinking water.

Some drinking water wells on western Long Island have been abandoned in recent decades because they became contaminated by seawater, and new research suggests that saltwater intrusion is increasing.

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

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

Extensive mapping efforts revealed that the saltwater “interface” in southwest Nassau, particularly in Long Beach, and in Inwood in northwest Nassau, has moved further inland than previously thought.

The report makes it clear that groundwater extraction is the cause. “The groundwater system on western Long Island has come under pressure from pumping from public wells, irrigation wells (golf courses) and industrial supply wells,” the authors write. When large amounts of groundwater are pumped out, salt water is absorbed from the coast.

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

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

According to the Environmental Protection Agency, Long Island residents use 70% more water per day than the national average. Water use roughly doubles in the summer, when lawns and golf courses use millions of gallons of water per day. According to the USGS, average daily water discharges during peak season in Nassau and Suffolk counties were about 242 million gallons and 358 million gallons per day, respectively.

Experts believe that without stricter protection measures, salt water will continue to seep into Long Island’s drinking water wells.

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

This needs to be investigated regionally and not just locally, because “abstractions from the centre of the island affect the water on the coasts, even if they hit us (on the coasts) first,” said Germain.

Some water districts have made efforts to encourage their customers to use less water through smart irrigation controls, such as preventing lawns from being watered when the ground is already wet. Starting Jan. 1, Port Washington residents will be required to use smart sprinkler systems.

That’s the “easy fruit to achieve,” says Germain – “that’s savings of 20 to 50%.”

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

The DEC did not comment on whether the findings justify such caps, but only said that the agency would examine the problem areas and work with suppliers to develop plans.