£EPA
Fact Sheet on Aquifer Exemption Data
Aquifer Exemption Data
EPA's interactive Aquifer Exemption map allows users to view electronically, for the first time, aquifers that EPA
approved for exemption under the Safe Drinking Water Act Underground Injection Control regulations. This interactive
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 depths of injection, local geology, and injected fluid characteristics, and can
assist with Underground Injection Control 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 requirements. Figure 1 shows simplified scenarios where a well owner/operator or a
state might request EPA to approve an aquifer
exemption.
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 US
There are more than 3,300 aquifer exemptions in
the United States. The majority are located in
Montana, Wyoming, Colorado, and Indian country,
as shown in Figure 2.
California is engaged in a process to digitize
existing aquifer exemption locations and is also
currently reviewing numerous requests for new or
expanded aquifer exemptions that they expect to
submit to EPA for review. The EPA is also working
closely with Texas to better understand the
locations of some of their aquifer exemptions. As
this work progresses, the aquifer exemptions in
California and Texas will be added to the national
dataset.
Simplified Schematic Showing Scenarios Where
Aquifer Exemptions Might be Requested
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.
EPA 810-S-16-009 June 2019

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£EPA
Fact Sheet on Aquifer Exemption Data

Well Class (centrolds)

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~ Class II*

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~ Class MR
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~ Class III
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~ Class V

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County location available

only
Figure 2. The EPA approved approximately 3,300 aquifer exemptions as of November 2018. 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 proposed to inject into the exempted aquifer. Locations of aquifer exemptions in California
and Texas will be updated as information becomes available.
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. 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 11R) and one-third are for disposal of wastewater (Class IID). 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 Class II rather than Class 11D or Class 11R. About three 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 other fluids.
Aquifer Exemption Depth
The shallowest depths of the exempted aquifers range from hundreds to thousands of feet below ground surface. About
two percent of aquifer exemptions are 500 feet or less below the surface at the shallowest point; most are between
1,000 and 9,000 feet deep. Some 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 public drinking water well depths
ranged from fifteen to 3,534 feet, with an average depth of 577 feet, below ground surface.2
1DeSimone, 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.
EPA 810-S-16-009 June 2019	2

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