Underground Injection Control (UIC) Program

Contact: Nathan Durant (207) 242-3483

What is the UIC Program?

The Underground Injection Control (UIC) Program was established by the federal Safe Drinking Water Act. The program protects underground sources of drinking water by regulating the subsurface discharge of both hazardous and non-hazardous pollutants through injection wells.

In Maine, the Department of Environmental Protection administers the UIC Program, with support from the U.S. Environmental Protection Agency (EPA). Maine's UIC Program was established in 1983, when the Board of Environmental Protection adopted rules to control the subsurface discharge of pollutants by well injection, chapter 543. The requirements of UIC Program enhance Maine's own subsurface wastewater discharge program.

What are Injection Wells?

An injection well is any bored, drilled or driven shaft, or dug hole whose depth is greater than its largest surface dimension; an improved sinkhole; or a subsurface distribution system used to discharge fluids underground.  These wells range from deep, highly technical, and more frequently monitored wells to shallow on-site drainage systems, such as septic systems, cesspools, and storm water drainage wells.

The federal UIC Program defines five categories or "classes" of injection wells based on function, construction, and operating features.

  • Class I wells isolate hazardous, industrial and municipal wastes through deep injection. Class I wells inject hazardous and non-hazardous wastes into deep, isolated rock formations below the lowermost aquifer. For example, Class I wells are used by industries such as petroleum refining and metal, chemical and pharmaceutical production to inject hazardous wastes up to 2 miles below the ground surface. There are specific siting, construction, operating, monitoring and testing, reporting and record keeping, permitting and closure requirements for all Class I wells.

  • Class II wells inject oil and gas production wastes and materials. Class II wells inject fluids associated with oil and natural gas production. Most of the injected fluid is brine pumped to the surface along with oil and gas. This brine is often saltier than seawater and can contain toxic metals and radioactive substances. By injecting the brine, Class II wells prevent surface contamination of soil and water. In addition, well operators inject residual brines, steam, polymers, and other fluid to enhance the production of oil and gas. Class II well operators must follow strict construction and conversion requirements.

  • Class III wells minimize environmental impacts from solution mining operations. Class III wells inject fluids into rock formation to dissolve and extract minerals. The injected fluids are pumped to the surface and the minerals in solution are extracted. Generally, the fluid is recycled into the same formation for further mineral extraction. More than 50 percent of the salt and 80 percent of the uranium extraction in the United States involves Class III injection wells.

  • Class IV wells prevent ground water contamination by prohibiting the shallow injection of hazardous waste except as part of authorized ground water cleanup activities. Class IV wells are shallow wells used to inject hazardous or radioactive wastes. They are banned except when operated to inject treated contaminated ground water back into the original aquifer. Class IV wells can be operated only with federal or state approval under the RCRA or Superfund programs.

  • Class V wells manage the shallow injection of all other fluids. Class V wells are all other injection wells that are not included in Classes I through IV. Class V wells inject non-hazardous fluids into or above an aquifer. They are typically shallow, on-site subsurface disposal systems, such as floor drains that discharge into dry wells, septic systems, leach fields, and similar types of drainage systems. When properly designed and operated, Class V wells should not endanger ground water. Examples of Class V wells include:
    • Stormwater Drainage Wells used to remove storm water and urban runoff from surfaces such as roadways, roofs, and paved surfaces to prevent flooding;
    • Aquifer Recharge Wells used to re-supply dwindling ground water resources;
    • Fluid Return Wells receive discharges of water that has been used for heating or cooling a heat pump;
    • Large-capacity Septic Systems with septic tanks and disposal fields that receive solely domestic wastewater and have the capacity to serve 20 or more persons per day or dispose of 2,000 or more of domestic wastewater per day; and
    • Other Injection Wells that receive non-hazardous, industrial and commercial wastewater, such as wastewater from manual car washes; snowmelt from cars and trucks; non-contact cooling water; and filter backwash from swimming pools and hot tubs.

How are these classes of injection wells regulated?

Class I, II and III wells are prohibited in Maine under Rule 06-096 ch. 543 3(c). Class IV wells, other than those used at RCRA or Superfund sites, are also prohibited in Maine.

Most Class V wells, including all those listed above, are authorized by rule. An owner or operator of a Class V injection well who registers the well with the DEP can discharge to that well as long as the discharge activity does not endanger ground water. Some other types of Class V wells not listed above represent a greater threat to ground water and the DEP has requires owner of these wells to receive a waste discharge license prior to discharging. Finally, two types of Class V wells -- motor vehicle waste disposal wells and large-capacity cesspools -- are prohibited by state and federal law.

Are there injection wells the UIC Program does not regulate?

The UIC Program does not regulate individual or single-family septic systems and "grandfathered" cesspools nor does it regulate non-residential septic systems or "grandfathered" cesspools provided these systems solely receive domestic wastewater and have the capacity to serve fewer than 20 persons per day or dispose of less than 2,000 gallons per day of wastewater. However, in Maine, these discharges are regulated by local and state officials under the Maine Subsurface Wastewater Disposal Rules.

What should I do if I have a Class V well?

If you have a type of Class V well that is authorized by rule, then you should register the well with the DEP.

If you are unsure of the type of Class V well or you have a type of Class V well that requires a waste discharge license to operate or is prohibited, you should contact the Division of Water Quality Management at the DEP, telephone 287-7688. The DEP can help you determine the appropriate and legal regulatory approach to your subsurface injection of wastewater.