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Primary & Principal Aquifers

About one quarter of New Yorkers rely on groundwater as a source of potable water. In order to enhance regulatory protection in areas where groundwater resources are most productive and most vulnerable, the Department of Health, in 1980, identified eighteen Primary Water Supply Aquifers (also referred to simply as Primary Aquifers) across the state. These are defined in the Division of Water Technical & Operational Guidance Series (TOGS) 2.1.3 as "highly productive aquifers presently utilized as sources of water supply by major municipal water supply systems".

All of the Primary Aquifers have been mapped in detail at a scale of 1:24,000. They are available as United States Geological Survey (USGS) reports. The map above shows the locations of Primary Aquifers and their names. Click on this map to see a larger image in which the aquifers are linked to their respective USGS reports. To search for additional USGS publications, click on the USGS Search Engine link in the right margin.

Small map of Primary and Principal Aquifers in NYS
Primary and Principal Aquifers in New York State. For detailed
mapping see the USGS websites listed in the right margin of|
this webpage. Click map to view a larger version.

Another category listed in TOGS 2.1.3 is Principal Aquifers. These are "aquifers known to be highly productive or whose geology suggests abundant potential water supply, but which are not intensively used as sources of water supply by major municipal systems at the present time". Although extensive mapping coverage exists at a 1:250,000 scale, map coverage at 1:24,000 is incomplete.

More information about detailed aquifer mapping is available on DEC's Groundwater Resource Mapping page.

The USGS and NYSDEC cooperative mapping program, started thirty years ago, has resulted in almost forty 1:24,000 scale mapped Primary and Principal Aquifers. However, due to the large number of aquifers in New York State, the program must continue for some time before all the larger Principal Aquifers have been mapped at this detailed scale. In the meantime, for those areas not mapped at a 1:24,000 scale, the Division of Water refers to a USGS series of five plates titled "Unconsolidated Aquifers In Upstate New York", mapped at a scale of 1:250,000. Areas mapped as "Unconfined Aquifer 10 to 100 gallons per minute" or "Unconfined Aquifer more than 100 gallons per minute" are considered to be Principal Aquifers unless contradictory site specific information is made available to the Department.

The five plates are listed below and are available online; see the right margin of this webpage for the links.

A New York state map with 5 color-coded plates of aquifer

Finger Lakes sheet - - WRI 87-4122
Lower Hudson sheet -- WRI 87-4274
Hudson-Mohawk sheet - - WRI 87-4275
Adirondack sheet - - WRI 87-4276
Niagara sheet - - WRI 88-4076

When consulting these 1:250,000 scale maps it is important to keep in mind that the level of detail is limited and thus the maps show only the general extent of the aquifers. They were not intended for detailed site evaluations. Determination of the precise location of aquifer boundaries or of well yields may require additional data.

GIS Data Set

A GIS data set containing the mapping of 1:24,000 scale Primary and Principal Aquifers (outside link leaving DEC's website) is available at the NYS GIS Clearinghouse. Enhancements were made to these maps to create digital, georeferenced map layers. The digital map layers contain original mapping units and aquifer boundaries as well as new standardized mapping units and updated aquifer boundaries. The original published aquifer maps contain additional base and geologic information not included in these map layers.


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