Underground Injection Control
What is Underground Injection?
Underground injection is the technology of placing fluids underground, in porous formations of rocks, through
wells or other similar conveyance systems. While rocks such as sandstone, shale, limestone appear to be
solid, they can contain significant voids or pores that allow water and other fluids to fill and move
through them. The fluids may be water, wastewater or water mixed with chemicals.
Why Do We Need a Program to Regulate the Placement of Fluids Underground?
When wells are properly sited, constructed, and operated, underground injection is an effective and
environmentally safe method to dispose of wastes. The Safe Drinking Water Act established the
Underground Injection Control (UIC) Program to provide safeguards so that injection wells do not endanger
current and future underground sources of drinking water (USDW). The most accessible fresh water is
stored in shallow geological formations called aquifers and is the most vulnerable to contamination. These
aquifers feed our lakes; provide recharge to our streams and rivers, particularly during dry periods; and
serve as resources for 92 percent of public water systems in the United States.
What Is an Injection Well?
The UIC Program defines an injection well as any bored, drilled or a driven shaft or a dug hole, where the
depth is greater than the largest surface dimension that is used to discharge fluids underground. A
drainfield is considered to be a horizontally placed injection system, and some drainfields are covered
under the UIC Program.
How Does the UIC Program Regulate the Very Different Types of Underground
The EPA groups underground injection into five classes for regulatory control purposes. Each class includes
wells with similar functions, and construction and operating features so that technical requirements can be
applied consistently to the class.
- Class I includes the emplacement of hazardous and nonhazardous fluids (industrial and municipal wastes)
into isolated formations beneath the lowermost USDW. Because they may inject hazardous waste, Class I
wells are the most strictly regulated and are further regulated under the Resource, Conservation and
- Class II includes injection of brines and other fluids associated with oil and gas production (Class II
injection wells are regulated by the ND Oil
& Gas Division);
- Class III encompasses injection of fluids associated with solution mining of minerals (Class III
injection wells are regulated by the ND
- Class IV addresses injection of hazardous or radioactive wastes into or above a USDW and is banned
unless authorized under a supervised groundwater remediation project.
- Class V includes all underground injection not included in Classes I-IV. Class V wells inject
nonhazardous fluids into or above a USDW and are typically shallow, on-site disposal systems, such as
floor and sink drains which discharge directly or indirectly to groundwater, dry wells, leach fields,
and similar types of drainage wells.
- Injection practices or wells which are NOT covered by the UIC Program include;
- individual residential waste disposal systems that inject ONLY sanitary waste
- commercial waste disposal systems that serve fewer than 20 persons that inject
ONLY sanitary waste.
Are All Injection Wells Waste Disposal Wells?
All injection wells are not waste disposal wells. Some Class V wells, for example, inject surface water to
replenish depleted aquifers or to prevent salt water intrusion. Some Class II wells inject fluids for
enhanced recovery of oil and natural gas, and others inject liquid hydrocarbons that constitute our Nation's
strategic fuel reserves in times of crisis.
How Does the UIC Program Prevent Contamination of Our Water Supply?
Injection wells have the potential to inject contaminants that may cause our underground sources of drinking
water to become contaminated. The UIC Program prevents this contamination by setting minimum requirements.
The goals of the EPA's UIC Program are to prevent contamination by keeping injected fluids within the well
and the intended injection zone, or in the case of injection of fluids directly or indirectly into a USDW,
to require that injected fluids not cause a public water system to violate drinking water standards or
otherwise adversely affect public health. These minimum requirements affect the siting of an injection well,
and the construction, operation, maintenance, monitoring, testing, and finally, the closure of the well. All
injection wells require authorization under general rules or specific permits.
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