Long Island State of the Aquifer System

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One of the most important concepts to understand is that volumes of water pumped from a groundwater system must come from somewhere and must cause a change in the groundwater system. Another important concept is that water table aquifers are hydraulically connected to the streams that drain them. Therefore, pumping water from aquifers that are hydraulically connected with surface-water bodies can have a significant effect on those bodies by reducing groundwater discharges to surface water and possibly causing outflow from those bodies into the groundwater system. Thus, an evaluation of groundwater management strategies needs to involve consideration of surface-water resources, including closely related biological resources.

A key feature of Long Island’s groundwater system is the large volume of groundwater in storage, which allows the possibility of using aquifers for temporary storage, that is, managing inflow and outflow of groundwater in storage in a manner similar to surface-water reservoirs (Alley and others, 1999). The groundwater reservoir of Long Island is a wedged shaped mass of saturated unconsolidated deposits that overlie nearly impermeable consolidated bedrock and attain a maximum thickness of about 2,000 feet. The boundaries of the fresh groundwater reservoir are the water table, the fresh-salt water interfaces, the bedrock surface, and the streams. The estimated volume of material saturated with fresh groundwater is about 180 cubic miles, and an estimated 10-20 trillion gallons of freshwater would drain from these deposits if they could be completely dewatered (Franke and others, 1972).

From the standpoint of water use and water management, all groundwater is not equal--the suitability of water, as measured by its quality, is a key consideration in developing water-management strategies. Furthermore, determining water suitability (or unsuitability) requires detailed information on the three-dimensional distribution and concentrations of potential contaminants, both naturally occurring contaminants and those resulting from human activities (Alley and others, 1999).

Continued large withdrawals of water from an aquifer often result in undesirable consequences. From a management standpoint, water managers, stakeholders, and the public must decide the specific conditions under which the undesirable consequences can no longer be tolerated.

The effects of groundwater development may require many years to become evident. Thus, there is an unfortunate tendency to forego the data collection and analysis that is needed to support informed decision making until well after problems materialize (Alley and others, 1999).


Table of Contents

State of the Aquifer, Long Island, New York - Introduction

Location and Physical Setting


  1. Hydrolgeologic Units
  2. Fresh and Saltwater Relations/Interactions

State of the Aquifer System

  1. Precipitation
  2. NWIS - the USGS Data Archive 
  3. Surface Water - Streamflow
  4. Groundwater Levels
  5. Water Table and Surface Maps
  6. Water Use
  7. Groundwater Budget
  8. Inflow to the Groundwater System
  9. Outflow from the Groundwater System
  1. Case Studies

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