Drinking water source 'under stress': Study underscores burden on Long Island's aquifer

For years, conservationists have warned that too much drinkable water is being extracted from the aquifer — a critical repository deep below Long Island — but there wasn't a lot of recent data to define the extent of the problem.

That was until an eight-year study released in August found the aquifer is "under stress," leading to saltwater intrusion, draining of some groundwater-fed streams and abandonment of degraded public wells. The authors of the study, a collaboration between the U.S. Geological Survey and the state Department of Environmental Conservation, note some of these problems date back decades and have been exacerbated by climate change. 

"The findings are exactly what we anticipated," said Adrienne Esposito, director of Farmingdale-based Citizens Campaign for the Environment. "This study is a clear and critical warning that we must stop overpumping and start managing our aquifer in a sustainable way." 

Why saltwater shifted inland

As Long Island’s population grew over the past 75 years — Nassau’s population has more than doubled since 1950, and Suffolk’s more than quintupled — water use has increased, too. Today, roughly 400 million gallons are pumped from more than 1,500 public supply wells daily for household uses, according to the USGS. Agriculture and industry consume another 60 million gallons.

That’s still a tiny fraction of the estimated 50 trillion gallons of water stored underground, an immense and seemingly inexhaustible supply.

Although the water supply for the Island overall is not at risk, the report said, overpumping has caused the saltwater interface — the boundary where saltwater meets fresh groundwater — to shift inland in some areas. Monitoring wells in those areas, including in parts of Great Neck, Manhasset Neck, Inwood and Long Beach, now show elevated levels of chloride, a component of salt. This migration began in the 1940s in Nassau and spread to Suffolk by the 1970s. 

In Long Beach, for example, saltwater was seeping into the shallower layers of the aquifer by the 1940s. By 1979, monitoring wells showed concentrations of chloride reached 8,700 mg/L — nearly 35 times the EPA’s recommended maximum level for chloride in drinking water. Today, the city’s wells draw from the Lloyd aquifer, more than 1,000 feet underground, where the groundwater is untainted.

It’s not a question of the aquifer running dry, Sarah Meyland, a former professor of hydrology at the New York Institution of Technology, explained.

"There will always be water in the aquifer system," she said. "It’s just a question of, is it going to be freshwater or is it going to be saltwater?"

Local streams are depleted

A healthy aquifer maintains a balance between water that flows out and water that flows back in from rainfall and snowmelt. For thousands of years before the first well was dug, groundwater flowed from the aquifer into Long Island’s streams, ponds and lakes. When large amounts are withdrawn for human use, the aquifer begins to run a deficit.

Even small drops in the groundwater levels can cause trouble — above ground, as well as below.

If the groundwater level falls lower than a lake or stream bed, groundwater no longer flows into that lake or stream.

"People say the aquifer is 1,500 feet deep; there’s plenty of water," said John Turner, senior conservation policy advocate at the Seatuck Environmental Association, based in Islip. "But if it drops to 1,490 feet, you’ve lost all your surface wetlands." 

That effect has been spotted across Long Island. 

These days, Massapequa Creek slows to a trickle in dry years. Meadowbrook, which once ran through a meadow in Hempstead Plains, appears to be another casualty of development and overpumping.

"Hempstead Plains has been almost entirely destroyed, the meadow doesn’t exist and the brook is a remnant of what it once was," Turner said.

Coastal wetlands and estuaries are affected, too: When groundwater stops drifting in, it upsets the delicate balance of fresh and saltwater that many coastal species depend on.

Global heating exacerbates these effects, as higher temperatures bring rain in heavy downpours, much of which is lost to runoff.

Conserving water to preserve the aquifer

Long Islanders use 70% more water than the national average, according to data from the USGS. And consumption doubles or even triples in summer, mainly because of lawn irrigation. But scattered efforts to conserve water have not always been effective.

In 2017, after several years of below-average rainfall, the DEC required public water suppliers to develop plans to reduce peak season pumpage by 15%.

The results have been underwhelming, according to figures from a 2023 report from the Long Island Commission for Aquifer Protection, a consortium of public officials and water supply professionals. Last year, summer pumpage in Nassau County was 3.5% lower than the average for the previous decade; in Suffolk, water use actually increased.

Several experts said that smart sprinklers, which prevent watering when the soil is already wet, can significantly reduce water waste. Roslyn and Port Washington, among others, have been promoting these for years; by Jan. 1, residents will be required to replace standard sprinklers with the smart versions.

Conservationists have identified another tempting target for large-scale water savings: Long Island’s golf courses, which are carpeted in nearly 10,000 acres of lawn grass. Since 2016, the Indian Island golf course in Riverhead has been watering its links with water reclaimed from the town’s nearby sewage treatment plant — a savings of 63 million gallons each year.

Of the 140 courses in Nassau and Suffolk counties, 49 are within two miles of a wastewater treatment facility, according to an analysis by Seatuck and the Greentree Foundation, and could be good candidates for reclamation.

An added benefit: Recycling water instead of releasing it into waterways diverts excess nitrogen from ecologically fragile bays and estuaries.

For some experts, the new data confirms the vast aquifer is a limited resource after all. "Groundwater is a public resource held in the public trust," Esposito said. "It is the most essential factor that our island needs to be habitable, and it needs to be managed holistically to keep it clean and sustainable."