Earth Matters: Long Island’s aquifer can be sustained

The Island Now

By Jennifer Wilson Pines

Here on Long Island we live on top of our drinking water. Unlike the city, our water does not come from streams, lakes or reservoirs, but is pumped from underground aquifers. This is our sole source of drinking water, which is also used for irrigation, commercial and manufacturing uses. The aquifer consists of three layers, the Upper, the Magothy and the lowest layer, the Lloyd. They are separated by layers of clay and vary in depth in different areas of the island.

To understand our aquifers, you need to understand how the island was formed. During the Pleistocene Ice Age multiple waves of glaciers from 2.6 million years ago to as recently as 11,000 years ago flowed across the continent. Imagine a 2,000 foot-high sheet of ice scouring the landscape, pushing ahead a mountain of boulders, rocks, clay and sand until it reached a limit where the temperature restrained it from advancing. During the Ice Age, so much water was locked up in the ice sheets that sea level was 150 to 400 feet lower — the beach would have been about 100 miles offshore.

This giant pile of debris is known as a terminal moraine. Long Island was created by the Harbor Hill Moraine and Ronkonkoma Moraine, which run the length of Long Island. When you drive the LIE, you are roughly following the moraine. The islands off Orient Point — Plum and Little Gull — are part of the moraine that continues on underwater toward Rhode Island.

The rocky North Shore, with its cliffs and high hills, is where the glaciers stopped their movement. Over time the fine grain sands washed out to the south, creating the flat outwash plain and wide beaches of the South Shore. This formation makes the geology of the island and particularly the North Shore, very complicated.

Aquifers are not giant pools of water underground, but areas of sand and gravel that can hold millions of gallons of water. If you took a cross-section slice running north south across the island, the aquifers would look like long wedges, with the shallow end at the North Shore becoming deeper and wider to the south.

The Upper layer was formed by material laid down during the Ice Age. It is no longer used by municipal suppliers, but there are homes on the East End that still rely on private wells. The next layer, the Magothy, is exposed at the north end- that’s why there are so many springs and small streams on the North Shore. The lowest layer, the Lloyd, is prehistoric water. The Lloyd is reserved for coastal communities suffering from saltwater intrusion. The island is surrounded by sea water and as wells near the coast pump out fresh water, saltwater is drawn in.

The aquifers are recharged by rain and snow percolating down, taking from 25 to 1,000 years. As the island has become more populated, more ground has been covered with impervious surfaces, buildings, driveways and parking lots, places where water can’t soak into the soil. And at the same time, more and more water is being withdrawn than is recharging. The United States Geological Surver is doing a survey of the aquifers so that for the first time in decades, water suppliers and municipalities will have actual numbers to set realistic pumping caps. While the island is not in a water crisis yet, it is looming on the horizon.

There are several issues facing us. Contamination from past and present industry has forced suppliers to invest in expensive equipment to clean the water. In some cases, contamination has forced the closure of wells. Contamination also comes from the nitrogen in fertilizers and septic systems, pesticides and herbicides.

Stormwater systems built over the last century were designed to capture and direct the water into the nearest body of water, often a bay. There are recharge sumps, but they don’t capture enough. At the same time, sewage treatment plants take the wastewater from our homes, treat it and pump millions of gallons of freshwater into the ocean every day. There are some pilot programs to reuse this gray water for irrigation on golf courses and parks.

Simple things can make a difference if done by the 3 million Long Islanders. Turn off the tap when brushing teeth, washing dishes, and the many times a day we all now wash our hands. Make sure sprinklers don’t water roads, sidewalks and driveways. Put a rain sensor on your irrigation system or turn it off when rain is forecast. Better yet, learn to live with dormant (brown) grass during the hottest part of the year. Only run the washing machine and dishwasher when you have a full load.

Think globally about your indirect water usage, the water used to produce products and foods, because access to clean water is a worldwide issue. Eat less beef – 1,800 gallons goes into producing every pound of beef. Switch to tea, much less water intensive than coffee. Consume more local foods, cut out sugary drinks- each one equals several bathtubs of water in sugar production, manufacturing and packaging. Take a tip from Australia, put a bucket in the tub to catch the water wasted while you wait for it to warm up. Use it for watering plants.

This problem will only be solved with everyone’s cooperation. Water on Long Island is not an unlimited resource.

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