From the Group's new "Freshwater Bulletin"

Long Island's groundwater system is unique and often misunderstood. Beneath all of Long Island, there are three aquifers or water bearing layers of sediment. The Lloyd is the deepest, ranging in depth from 200 feet below sea level on the north shore, to 1600 feet below sea level on the south shore and is topped by a layer of clay referred to as the Raritan Clay Layer. This confining clay layer is virtually impenetrable and protects the Lloyd from contamination. The Magothy Layer lies over the clay layer, and directly above the Magothy sits the Upper Glacial Aquifer. These layers are unconfined and are therefore more susceptible to contamination. Fresh water within these layers exists in the shape of a lens that lies above salt water. The areas near the north and south shores have considerably less water beneath the surface than the area in the center of the Island.

Because of the East End's small land mass and large shoreline area, it has a small fresh water lens. In fact, the lens is so thin that on much of the East End the Upper Glacial Aquifer is the only aquifer that contains fresh water. The rest of Suffolk and Nassau County has a Magothy Aquifer that supplies a large amount of fresh drinking water. The Lloyd Aquifer has a large area that naturally contains salt water. The only source of recharge for this aquifer system is precipitation, which falls to the earth in the form of rain and snow. The size of the fresh water lens is directly affected by how much rain enters the aquifer and how much is removed by wells. Every time the land is paved, another area where rain might enter into the groundwater reserve is removed. An increase in the pumping of private and public wells also decreases the amount of water available for the system. When these actions upset the balance and water leaving the aquifer (discharge) is greater than the amount of water entering the aquifer (recharge), salt water will move further up into the fresh water lens. Such salt water intrusion is the cause of chloride contamination of wells in Nappeague as well as areas of Montauk.

Contrary to popular belief, groundwater does not flow quickly in streams beneath Long Island. Within the aquifer system, groundwater's horizontal movement through the small pores that exist between soil particles is quite slow. In fact, horizontal groundwater movement from the mainland towards the ocean or bay in most areas is at a rate of about .5 to 2 feet per day. Water's vertical rate of infiltration into the aquifer is faster than the horizontal rate and is dependent on many complex factors. Because contamination in water generally moves at the same rate as the water in which it is found, pollutants quickly enter into the system and slowly move within the aquifer before they are discharged into wells or surface water bodies. Contamination from human activities enters the system every day, just below the ground's surface. Small actions of individuals, such as pouring motor oil or paint on the ground and larger sources of pollution, like leaking landfills or excessive pesticide use, all cause well contamination. To properly protect drinking water, it is necessary for people to understand the direct link between actions on the surface and the quality of groundwater below. This knowledge must be gained quickly because the quality of our water supply is rapidly deteriorating.

Our single aquifer system is the only source of water for all of Long Island. Even the public water that is brought through pipes originated somewhere within the same system. This is why it is so important for everyone do their part to protect the entire aquifer system and recognize that when it comes to groundwater quality, we all live downstream