vvEPA
Fact Sheet on Aquifer Exemption Data
Aquifer Exemption Data Release
EPA's interactive map allows users to view electronically for the first time aquifers that EPA has approved for exemption
under the Safe Drinking Water Act Underground Injection Control (UIC) regulations. EPA's Aquifer Exemption Map
brings together data previously available only in paper form or at the state level. The map and accompanying data can
be used by states, businesses, communities, and others to view exempted aquifers in the United States, see
accompanying aquifer exemption data like depth of injection, local geology, and injected fluid characteristics, and can
assist with UIC permit applications and approvals.
Background on Aquifer Exemptions
An aquifer is an underground body of rock that provides or could provide ground water to support people's needs. EPA
exempts aquifers if the aquifer does not currently serve as a source of drinking water and will not serve as a source of
drinking water in the future, based on certain criteria. Aquifer exemptions allow these underground sources of water to
be used by energy and mining companies for oil or
mineral extraction or disposal purposes in
compliance with EPA's Underground Injection
Control (UIC) requirements. Figure 1 shows
simplified scenarios where a well owner/operator or
a state might request EPA to approve an aquifer
exemption.
Simplified Schematic Showing Scenarios Where
Aquifer Exemptions Might be Requested
The process begins when EPA receives information
about the aquifer proposed for exemption from a
state agency or well owner or operator. EPA
approves the aquifer exemption request if it meets
the necessary criteria. Injection of fluids can begin
only after EPA approves an aquifer exemption and an
underground injection control permit is granted.
Summary of Data on Aquifer
Exemptions in the United States
There are about 3,300 aquifer exemptions in the US.
The majority of these are located in Montana,
Wyoming, Colorado, Utah, Texas, and Indian country,
as shown in Figure 2. Aquifer exemptions also exist in
California, which are not shown in Figure 2.
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. The EPA is also working closely with
Texas to better understand cases where Texas
An aquifer exemption may be required
to produce oil, natural gas, or minerals
from an aquifer
The EPA developed the aquifer exemption
process to protect drinking water aquifers and
meet industry needs. An aquifer exemption
allows fluid that might otherwise endanger a
drinking water source to be placed into a specific
portion of an aquifer. The EPA evaluates the
boundaries of the aquifer exemption proposed
by the well owner/operator or state so that
nearby drinking water sources remain protected.
The boundaries are shown for illustration
purposes as yellow dashed lines in this figure.
An aquifer exemption may be required to
place wastes from industrial processes into
portions of aquifers.
Aquifer mixed
with oil, natural
gas, or minerals
Rock layers that
protect overlying
aquifers from
contamination
Figure 1. Simplified schematic showing scenarios where aquifer
exemptions might be requested. The EPA evaluates proposed
aquifer exemption boundaries where fluids may be injected while
continuing to protect nearby drinking water sources. The
boundaries are shown for illustration purposes as yellow dashed
lines.
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v>EPA
Fact Sheet on Aquifer Exemption Data
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Figure 2. The EPA has approved approximately 3,300 aquifer exemptions as of January 2016. The map shows a point for the
center of each aquifer exemption or a county outline for those exemptions with imprecise locational information. Points are
color coded by the class of injection well proposed to inject into the exempted aquifer. Locations of aquifer exemptions in
California will be updated as information becomes available.
should have requested an exemption for Class II wells injecting oil and gas-related fluids.
Injection Activities Associated with Exempted Aquifers
Aquifer exemptions requested to date are usually associated with three of the six classes of injection wells regulated by
the EPA Underground Injection Control program (see Figure 2). About 95 percent of aquifer exemptions are associated
with Class II wells for injection of fluids related to oil and gas production. Almost two-thirds of aquifer exemptions
associated with Class II wells are for enhanced oil or gas recovery (Class MR) and one-third are for disposal of wastewater
(Class 11D). A small percentage of the aquifer exemptions are not associated with specific Class II activities such as
enhanced recovery or disposal; those aquifer exemptions are designated as Class II rather than Class 11D or Class MR.
About two 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.
Aquifer Exemption Depth
The depth of the exempted aquifers ranges from hundreds to thousands of feet below ground surface. About one
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.
For comparison, the depths of private drinking water wells measured across the United States ranged from six feet to
1,500 feet below ground surface with an average depth of 172 feet.1 The depths of measured public drinking water wells
ranged from fifteen to 3,534 feet with an average depth of 577 feet below ground surface.2
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Fact Sheet on Aquifer Exemption Data
Aquifer Exemption Boundaries
The boundary of an aquifer exemption contains the portion of the aquifer that may be affected by the injection activity.
Aquifer exemption boundaries are determined in a variety of ways. Some aquifer exemptions are defined as a radius
(typically / or Vz 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 65 percent are % 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.
For More Information
For additional information on aquifer exemptions, including the requirements at 40 CFR 146.4, see
https://www.epa.gov/uic/aquifer-exemptions-underground-iniection-control-program.
For additional information on the UIC program, see https://www.epa.gov/uic.
To download the geospatial file and related materials, visit https://www.epa.gov/uic/aquifer-exemptions-map.
For information on specific aquifer exemptions, contact the EPA Regional Office that approved the aquifer exemption;
contact information is available at https://www.epa.gov/uic.
Visit the Safe Drinking Water Hotline at https://www.epa.gov/ground-water-and-drinking-water/safe-drinking-water-
hotline or 1-800-426-4791 for help with data-related questions or the Aquifer Exemptions Map.
'DeSimone, LA, Hamilton, PA, Gilliom, RJ. 2009. Data from Quality of water from domestic wells in principal aquifers of the United States, 1991-2004. US Geological
Survey.
2Toccalino, PL, Hopple, JA. 2010. Data from The quality of our Nation's waters—Quality of water from public-supply wells in the United States, 1993-2007. US
Geological Survey.
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