Long Island is made up of a series of sand and gravel aquifers. All of Long Island's water supply comes from underground water held in aquifers. An aquifer is a geologic formation, which can hold, transmit and yield water in usable quantities. Clay layers between certain aquifer layers act to retard some water movement beneath the island. Stacked one on top of the other like layers in a cake, three major and one minor aquifer make up the Long Island aquifer system.
- Long Island Hydrology: How Groundwater Flows
- Myths and Facts About Long Island Groundwater
- Water Conservation
- CCE Testimony for NYS Assembly Hearing on Long Island Drinking Water Protection
Long Island Groundwater Resources
"Water Worries" - a report summarizing reactions to the draft of the Suffolk County Comprehensive Water Resources Management Plan by some of Long Island's leading environmental groups, including Citizens Campaign for the Environment, Group for the East End, Long Island Pine Barrens Society, The Nature Conservancy, and Peconic Baykeeper.
Long Island Groundwater
In sequence from shallowest to deepest, the LI aquifers are: the Upper Glacial, the Magothy and the Lloyd Aquifers. A minor aquifer, the Jameco, lies beneath the Upper Glacial, along the western south shore of Long Island. All of the aquifers slope downward toward the southern portion of the island. This causes the deepest parts of the aquifers and the groundwater system to reside along the southern shore of Long Island, and extends out into the subsurface material beneath the ocean floor.
The aquifer formations beneath Long Island were deposited at different times in the area's geologic history. The deepest aquifer layer, the Lloyd, rests on a bed of consolidated bedrock, primarily igneous and metamorphic. The bedrock was laid down in the Precambrian Era, making it older than 600 million years. The sand deposits of the Lloyd Aquifer were laid down in the Cretaceous Period, about 80-100 million years ago. The sand and gravel of the Magothy aquifer was deposited in the upper Cretaceous Period, about 50-80 million years ago. The youngest aquifer formation, the Upper Glacial, was laid down during the last ice age, 10-15 million years ago. It contains course sands, pebbles, rocks and occasionally boulders, carried to Long Island and left behind by the glaciers. The water table, or the top of the groundwater system, is found in the Upper Glacial aquifer.
A thick deposit of clay (100-200 feet thick) called the Raritan Clay exists between the Magothy and Lloyd aquifers. The Lloyd sands and the clay bed above it are together known as the Raritan Formation. The Lloyd aquifer is found along the north shore of Long Island at depths averaging 200-300 feet. Along the southern shoreline the Lloyd aquifer is approximately 1,500 feet below the land surface. Along the south shore a second clay bed separates the Upper Glacial aquifer from the Jameco aquifer. It is called the Gardiners Clay. Clay units have very low permeability and act as aquitards, minimizing water exchange between the layers
All Long Island aquifers receive their fresh water from precipitation. Long Island receives, on average, about 44 inches of precipitation a year. Of this, about half of the precipitation, or approximately 22 inches of rain, percolates into the ground and is recharged into the groundwater system. The remaining precipitation is either evaporated, taken up by plants, or runs off into creeks, bays and estuaries. In areas where the water table and the ground surface meet, streams, ponds and wetlands are formed. In an undisturbed natural setting, (e.g., before human activities) all of Long Island's groundwater would ultimately reach the coast where the groundwater would mix with and the ocean. Due to human activity, this process has been significantly changed so that not all water in the groundwater system is returned to the ocean.
Today, groundwater is withdrawn from the system constantly. Over 138 billion gallons of water is taken each year from beneath Nassau and Suffolk Counties. In coastal areas, as water is drawn up for use, less groundwater is available to be discharged into the estuaries. The resulting loss of water and pressure allows saltwater from the ocean to flow into the aquifer, causing the groundwater to become saline, resulting in a condition called "saltwater intrusion".
New water from precipitation is constantly recharging, or replenishing, the aquifers. Unfortunately, as water recharges the system, it can easily carry contaminants with it into the groundwater. Since it is the shallowest and closest to most sources of contamination, the Upper Glacial aquifer is the most heavily contaminated of the three. The next most seriously contaminated aquifer is the Magothy, which is the layer below the Upper Glacial. The Magothy aquifer supplies over 90% of the water used in Nassau County and about 50% of all water used in Suffolk County.
Although water can flow from one aquifer to another, groundwater on Long Island generally travels in a easterly direction. This horizontal movement offers some protection for deeper aquifers, however pollutants can still contamination aquifers below the Upper Glacial.
CCE works to Protect the Long Island Aquifer System
VICTORY! On September 26, 2008, the Long Island Lloyd Aquifer Protection Bill was signed into law. This important legislation ensures continued protection of Lloyd Aquifer. The legislation also ensures that NYC will not be able to pump or store water from the Lloyd Aquifer for their drinking water needs.
Thank you to all our members who made phone calls and wrote letters to the Governor asking him to sign the legislation.
Long Island has been designated as a sole-source aquifer region by the U.S. EPA. This means that 100% of our drinking water supply comes from underground. The almost 3 million residents on our island are completely dependent on groundwater as our fresh water supply.
The Lloyd aquifer is the deepest and cleanest source of drinking water on Long Island.
Yet, NYC was aggressively seeking to use Long Island’s aquifer as a storage facility for their own drinking water.
Their plan was to initiate a pilot program beginning with the injection of 300-400 gallons of water per day into the Lloyd Aquifer. This would then lead to a large scale project of injecting 50 million gallons per day into the Lloyd aquifer in Queens. After 5 years, the artificially recharged Lloyd Aquifer would be tapped to supply up to 200 million gallons a day for two years back to NYC.
This critical legislation takes necessary steps to safeguard the Lloyd Aquifer, an irreplaceable drinking water resource, and stop any proposals that would permit the misuse of this resource. Thanks again to all our members who have taken time to voice your concerns. Our voices were heard and our oldest and deepest source of drinking water is forever protected from risky proposals.
Updated by bsmith 2/26/13