An official website of the United States government.

This is not the current EPA website. To navigate to the current EPA website, please go to This website is historical material reflecting the EPA website as it existed on January 19, 2021. This website is no longer updated and links to external websites and some internal pages may not work. More information »

Underground Injection Control (UIC)

Aquifer Exemptions Map

On this page:

Interactive aquifer exemptions map

EPA’s interactive map allows users to find locations of aquifers approved for exemption under the Safe Drinking Water Act UIC regulations. The website also provides geospatial files and Excel data with an accompanying user guide. The map shows the approved aquifer exemption boundaries, when available, in two dimensions, and information such as the depth of injection, local geology, and injected fluid characteristics. The Excel spreadsheet provides descriptive information from the geospatial file without geospatial data. Users may download the datasets and a user guide from the Downloadable Data section on this page or the map’s "Further Information" tab. 

decorative screenshot link to interactive GIS map

The aquifer exemption data and map were prepared by EPA as an informational tool to assist users in understanding the number, locations, and the nature and quality of aquifer exemptions approved by EPA. Changes are periodically made to the data and map as information becomes available.

Top of Page

Facts on aquifer exemptions

There are about 6,000 aquifer exemptions in the US. The majority of these are located in Montana, Wyoming, Colorado, Utah, Texas, and Indian country. Aquifer exemptions also exist in California, which are not shown in the Aquifer Exemption Map. California is engaged in a process to digitize existing exemption locations and is also currently reviewing numerous requests for new or expanded aquifer exemptions that they expect to submit to EPA for review.  As this work progresses, the aquifer exemptions in California will be added to the national dataset.

About 97 percent of aquifer exemptions are associated with Class II wells for injection of fluids related to oil and gas production. One-third of aquifer exemptions associated with Class II wells are for enhanced oil or gas recovery (Class IIR) and one-fourth are for disposal of wastewater (Class IID). About one percent of aquifer exemptions are associated with Class III wells, which assist in recovering minerals such as uranium and salts. The remainder are associated with Class I wells used to inject non-hazardous industrial wastes and others.

The depth of the exempted aquifers ranges from hundreds to thousands of feet below ground surface. About four percent of aquifer exemptions are 500 feet or less below the surface. Most depths are between 1,000 and 9,000 feet deep although a few are over 10,000 feet deep. In some cases, there is more than one exempted aquifer at the same location, but at different depths and in different bodies of rock.

Aquifer exemption boundaries are determined in a variety of ways. Some aquifer exemptions are defined as a radius (typically ¼ or ½ mile) around the well associated with the exemption and are circular. Others are defined by one or more grids in the Public Land Survey System and are squares or combinations of squares. Exemption boundaries can also be irregularly shaped and follow the dimensions of an aquifer, oil or gas field, or mining area. The exemption areas range in size from thousands of square feet to more than a thousand square miles (almost 38 percent are ¼ mi radius or smaller). Underground sources of drinking water in the surrounding area continue to be protected from endangerment under the Safe Drinking Water Act.

Top of Page

Aquifer exemption data initiative

To develop the dataset of aquifer exemption information, the EPA gathered available information about approved aquifer exemptions from its Regional offices and some state agencies. The Agency collected the aquifer exemptions information from paper files, spreadsheets, and databases generated over the past 35 years. A new, national dataset was created with the collected information.

The EPA developed a geospatial dataset that allows users to view or create a map of the aquifer exemption locations. The location of each exempted aquifer was converted from text descriptions to geospatial data. The text descriptions were recorded in multiple formats. A table of attributes associated with each aquifer exemption polygon includes information on the state, county, depth, geologic formation, lithology, approval date, and regulatory criteria met. More information on each attribute can be found in the data dictionary in the user guide.

The EPA developed an interactive Aquifer Exemption Map that allows users to find locations of aquifers approved for exemption under the Safe Drinking Water Act UIC regulations. Both the geospatial data and the attribute data are shown in the Aquifer Exemptions Map. Users can explore the data in the Aquifer Exemption Map or by downloading the files to create their own maps.

Top of Page

Downloadable data

Learn more about aquifer exemptions from downloadable files.

•    A user guide for aquifer exemptions data that describes how EPA developed the geospatial files shown in the Aquifer Exemptions Story Map and defines the data fields
•    A geospatial file with locations and information on each aquifer exemption (for use with geographic information system software).
•    An Excel spreadsheet  with information on each aquifer exemption.