Underground Injection Control Program
&EPA
United States
Environmental Protection
Agency
Protecting underground sources of
drinking water and public health
Storage or disposal of water and fluids may be managed
by injecting them underground using injection wells. Injection
wells are regulated by the Underground Injection Control
(UIC) program in order to protect underground sources of
drinking water.
The UIC program may be implemented by the United States
Environmental Protection Agency (EPA) or by states,
territories, or tribes with EPA-approved primary permitting
and enforcement authority. Activities performed by the UIC
program include maintaining well inventory, permitting
injection wells, performing inspections, and ensuring
compliance with permit requirements. When operators
manage wells in a way that does not meet the applicable UIC
requirements, the program alerts operators to issues and may
assist operators in returning the wells to compliance or take
enforcement action.
Types of Injection Wells
More than 740,000 injection wells were regulated by the
UIC program in 2018. Injection wells are found in ali fifty
states, territories, and tribal lands. Figure 1 shows the
relative numbers of injection wells by state.
The UIC program classifies injection wells based on the type
of fluids the well receives, the purpose of the
Toronto
Monterre^
injection, and where the fluid is injected relative to
underground sources of drinking water. Figure 2 shows the
number of wells by well class for 2018.
•	Class I wells are used to inject hazardous and non-
hazardous waste into deep, confined rock formations
below all underground sources of drinking water. The
fluids may include municipal, industrial, or radioactive
wastes.
•	Class II wells are used to inject fluids related to oil and
gas production.1 The majority of Class II wells are used to
enhance recovery of oil and gas or dispose of wastewater
co-produced with oil and gas into rock formations. Class II
wells represented approximately 25% of wells in 2018.
•	Class ill wells are used to inject fluids to aid in the
extraction of minerals such as uranium, salt, copper, and
sulfur.
•	Class IV wells are allowed in limited circumstances for
injection of groundwater treated as part of
environmental cleanup. Class IV wells are used to inject
hazardous and radioactive wastes into or above
underground sources of drinking water.
•	Class V wells are used to inject fluids that are not
classified as Class I, II, III, IV, and VI. Fluids injected into
Class V wells include stormwater and a wide variety of
other fluids. The construction of many Class V wells is
simple compared to Class I, II, III, and VI wells. Many Class
V wells may be little more than a shallow dug well with a
soil bottom. A minority of Class V wells are constructed
to be higher technology, especially if the wells inject into
deep rock formations. Figure 3 shows both simple and
more complex Class V wells. Class V wells represented
over 70% of wells in 2018.
•	Class VI wells are used to inject carbon dioxide deep
underground for long-term storage.
1 Class II wells do riot include fluids injected for purposes of hydraulic
fracturing except where diesel fuels are used.
Number of Wells by Class
600,000
' Figure 2. Most UIC wells are
at
§ 400,000
u
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Z 200,000
0
a*
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z
designated as Class II or
Class V.






1 II III IV
Injection Well Class
V
VI
Figure 1. EPA and state UIC Total Injection Wells
programs regulate more than	>75,000
740,000 injection wells as of
2018. An additional 6,528	55,000-75,000
injection wells in U.S. territories a
40 000-54 999
and tribal lands are not
displayed on the map.	• 20<00°-39<999
• 1-19,999
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Protecting Drinking Water and Public Health Through Underground Injection Control
Figure 3. Inspectors visit injection wells to ensure
protection of drinking water, (a) Class V stormwater well
(b) Class V aquifer storage and recovery well
Operators Receive Approval to Inject
In order to operate an injection well, operators must receive
approval through the UIC program. Some operators receive
approval by submitting information that describes the
operation such as well class, location, operating status, and
operator contact information to the UIC program. Other
operators need approval through a permit that identifies
specific operating conditions in order to inject. All wells must
be operated according to applicable UIC requirements.
The UIC program collects inventory data on all wells
authorized to inject (Figure 1) and the number of permits
issued each year. Figure 4 shows the proportions of permits
issued in 2018 by well class. The UIC program issued over
8,600 permits in 2018, which authorized more than 14,000
wells to inject.
Permits Issued by Well Class
Class
C ass , 0.8%
VI, n%	'
Class
IV,
0.03%
Class III,
0.4%
Class V,
21%
Figure 4. The
Figure 4.
Compliance is Key to Protection
The UIC program works with injection well operators
throughout the life of the well to confirm their practices do
not contaminate drinking water. The program conducts
inspections to verify compliance with the UIC
permit or applicable requirements. The program verifies the
following during an inspection:
•	Proper well construction,
•	No leaks from the well into the environment,
•	Monitoring, recordkeeping, and reporting are conducted
by the operator,
•	Any required operating conditions are followed, and
•	Proper well closure when operations end.
Almost 90,000 injection wells were inspected in 2018. Figure
5 indicates inspections performed by well class.
Despite the greatest number of wells being Class V, the
largest number of inspections were performed on Class II
wells. Class II wells tend to be technologically sophisticated
wells while many Class V wells are simply constructed and
rely on gravity to move fluids into the ground. Simple Class V
wells may be inspected a few times over their operating life
while Class II wells may be inspected annually or every few
years.
Injection Wells Inspected by Class
90,000
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— 60,000
84,317
Figure 5. The majority
of inspections were
performed on Class II
wells during 2018.
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30,000
453
406
27
IV
4,038
V
0
VI
Injection Well Class
Inspections are only one way that programs deter
noncompliance. Programs also evaluate periodic monitoring
reports submitted by operators and discuss potential issues
with operators.
If a well is found to be out of compliance with applicable
requirements in its permit or UIC regulations, the program
will identify specific actions that an operator must take to
address the issues. The UIC program may assist the operator
in returning the well to compliance. Assistance may include
discussing options or providing information to the operator.
In some cases, enforcement may be necessary to return a
well to compliance. Enforcement may include administrative
or judicial processes. The UIC program reported violations at
around 21,000 wells in 2018.
For more information on the UIC program, please visit
epa.gov/uic or email safewater@epa.gov.
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