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This map layer shows unconsolidated sand and gravel aquifers of alluvial and glacial origin, north of the southern-most line of glaciation. An aquifer is a geologic formation, group of formations, or part of a formation that contains sufficient saturated, permeable material to yield significant quantities of water to wells and springs. Alluvial aquifers are those that were deposited by a stream or other body of running water in a streambed, on a flood plain, on a delta, or at the base of a mountain. Glacial aquifers are formations that were deposited by a glacier. This map layer was compiled by the U.S. Geological Survey from a variety of sources.
Additional aquifer information is included in the National Atlas Principal Aquifers of the 48 Conterminous United States map layer. Information on aquifer types can be found on the Aquifer Basics page, and further water science information is available from the USGS Ground Water Information Pages, from the USGS Learning Web Explorers Water page, and from the Ground Water Atlas of the United States.
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What follows is very detailed technical information about this map layer. This is often called metadata. Metadata (or "data about data") describe the content, quality, condition, and other characteristics of data. Metadata are used to organize and maintain investments in data, to provide information to data catalogs and clearinghouses, and to aid data transfers. The Federal Geographic Data Committee (FGDC) publishes the Content Standard for Digital Geospatial Metadata. Many organizations within and outside of the federal government have adopted the FGDC metadata standard and are using automated indexing and serving mechanisms to provide access to their holdings through the Internet. Visit the FGDC Clearinghouse to learn more about how metadata is used in clearinghouses and to search for other data sets.
These data delineate the areal extent of the alluvial and glacial aquifers as defined in The Ground Water Atlas of The United States (GWA).
The aquifer outcrop and shallow subcrop boundaries represent broad, regional categories and should not be interpreted as site-specific. Comments regarding the names of aquifers or the hydrogeologic interpretation of the aquifers can be directed to the U.S. Geological Survey, Water Resources Division, Office of Ground Water, Roy Sonenshein, sunshine@usgs.gov, 305-717-5824.
These data were developed in conjunction with the publication of the GWA. For documentation purposes, areas are referred to by their corresponding GWA chapter letter, or by State. This list shows the relationship between State names and GWA chapters:
HA 730-B Segment 1-California, Nevada
HA 730-C Segment 2-Colorado, Utah, New Mexico, Arizona
HA 730-D Segment 3-Kansas, Missouri, Nebraska
HA 730-E Segment 4-Texas, Oklahoma
HA 730-F Segment 5-Arkansas, Louisiana, Mississippi
HA 730-G Segment 6-Alabama, Florida, Georgia, South Carolina
HA 730-H Segment 7-Idaho, Oregon, Washington
HA 730-I Segment 8-Montana, North Dakota, South Dakota, Wyoming
HA 730-J Segment 9-Iowa, Michigan, Minnesota, Wisconsin
HA 730-K Segment 10-Illinois, Indiana, Kentucky, Ohio, Tennessee
HA 730-L Segment 11-Delaware, Maryland, New Jersey, North Carolina,
Pennsylvania, Virginia, West Virginia
HA 730-M Segment 12-Connecticut, Maine, Massachusetts, New
Hampshire, New York, Rhode Island, Vermont
Refer to: <http://capp.water.usgs.gov/gwa/gwa.html> for a graphic
depiction of the GWA chapter regions, as well as more information about
the GWA.
Although these spatial data can stand alone, it may be helpful to refer to the printed GWA chapters when using the data. Note that the coastline was drawn from the National Atlas shoreline files and may not match the coastline shown in the GWA.
Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
Although this Federal Geographic Data Committee-compliant metadata file is intended to document the data set in nonproprietary form, as well as in Arc/INFO format, this metadata file may include some Arc/INFO-specific terminology.
The extent is based on the best available printed sources on the subject of aquifer extents. There is the potential that better data are available at the local level.
The remaining steps were completed using ArcGis 8.1 Workstation. The DXF file was converted to a coverage. Using the TRANSFORM command, the coverage containing the digitized aquifer extent lines was rubbersheeted to the coverage containing registration tics, it was then projected from geographic coordinates to the Albers Equal-Area Conic projection. An RMS error of less than 0.004 was accepted. If the RMS error was greater than 0.004 the location and values of the latitude/longitude points were verified.
The coverage was cleaned, the topology was built, and labels were added.
Attributes were added for the aquifer name (AQ_NAME), aquifer code (AQ_CODE), rock name (ROCK_NAME), and rock type (ROCK_TYPE).
The following items were verified:
--Transformation RMS error (below 0.004) --Arcs match the scanned film (no gaps between the plot and the compilation) --Arc and polygon topology exists --Coverage has a coordinate system defined --Attributes aq_name and aq_code have been added and populated correctly --Necessary files exist to redo any step