Long Island Water Suitability

Science Center Objects

Groundwater quality may be affected by natural and human factors (Johnston, 1988). Although the vulnerability of groundwater to contamination from the land surface is influenced by many factors, the degree of aquifer confinement, the depth of the well, and the surrounding land use are primary key factors that influence shallow groundwater quality.

Unconfined aquifers generally are much more vulnerable to contamination than confined aquifers. For a well in a confined aquifer, the farther the well is from the unconfined area, the less vulnerable it is to contamination. Generally, the deeper the well, the less vulnerable it is to contamination. Finally, because human activities greatly affect the quality of water that recharges an aquifer, the amount and type of land use in the area that contributes water to the well is a key factor in determining aquifer vulnerability to contamination (Clawges and others, 1999).

Two of the factors that have the greatest effect on groundwater quality are the land-use practices in the recharge area above the aquifer(s) and the groundwater-flow patterns within the aquifer(s) (Haefner, 1992).

map of  locations of contamination sites that have the potential to impact groundwater quality, in Nassau and Suffolk Counties

Figure 28. Generalized locations of contamination sites that have the potential to impact groundwater quality, in Nassau and Suffolk Counties, N.Y.(Source: U.S. Environmental Protection Agency).(Public domain.)


Groundwater quality data on Long Island has been collected for many years by the USGS and other Federal, State and local agencies. A recent map of contamination sites that have the potential to impact groundwater across Long Island is shown in Figure 28. This map was created by the U.S. Environmental Protection Agency, using information maintained by the New York State Department of Environmental Conservation.

Water Quality Data

The USGS collects and analyzes chemical, physical, and biological properties of water, sediment and tissue samples from across the Nation. The Water Data for the Nation discrete sample database is a compilation of over 4.4 million historical water quality analyses in the USGS district databases through September 2005. The discrete sample data is a large and complex set of data that has been collected by a variety of projects ranging from national programs to studies in small watersheds.

At selected surface-water and groundwater sites, the USGS maintains instruments that continuously record physical and chemical characteristics of the water including pH, specific conductance, temperature, dissolved oxygen, and percent dissolved-oxygen saturation. Supporting data such as air temperature and barometric pressure are also available at some sites. At sites where this information is transmitted automatically, data are available from the current data system.

There are over 4,200 sites on Long Island that had a water quality sample measurement taken since the early 1900's. The largest sample collections occurred between 1970-1990, where over 2,100 sites were sampled. Currently, for the period 2010-2014, only 117 sites have a water quality sample. Real time water quality data map service is available for several field parameters like water temperature.

  • Groundwater

Groundwater will normally look clear because the ground naturally filters out particulate matter. However, both natural and anthropogenic compounds can be found in groundwater. As groundwater flows through the ground, metals such as iron and manganese are dissolved and may later be found in high concentrations in the water. Industrial discharges, urban activities, agriculture, groundwater pumpage, and disposal of waste all can affect groundwater quality.

Contaminants can be human-induced, as from leaking fuel tanks or toxic chemical spills. Pesticides and fertilizers applied to lawns and crops can accumulate and migrate to the water table. Leakage from septic tanks and/or waste-disposal sites also can introduce bacteria to the water, and pesticides and fertilizers that seep into farmland can eventually end up in water drawn from a well. In some instances, a well might have been drilled in proximity to land that was once used for a landfill or chemical dump site. In any case, if you use your own well to supply drinking water to your home, it is wise to have your well water tested for chemicals and contaminates.

  • Surface Water

As watersheds are urbanized, much of the vegetation is replaced by impervious surfaces, thus reducing the area where infiltration to groundwater can occur. Thus, more stormwater runoff occurs — runoff that must be collected by extensive drainage systems that combine curbs, storm sewers, and ditches to carry stormwater runoff directly to streams. More simply, in a developed watershed, much more water arrives into a stream much more quickly, resulting in an increased likelihood of more frequent and more severe flooding.

As it flows over the land surface, stormwater picks up potential pollutants that may include sediment, nutrients (from lawn fertilizers), bacteria (from animal and human waste), pesticides (from lawn and garden chemicals), metals (from rooftops and roadways), and petroleum by-products (from leaking vehicles). Pollution originating over a large land area without a single point of origin and generally carried by stormwater is considered non-point source pollution.


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

Interactive Content