Underground Injection Control (UIC)


The subsurface environment has been utilized for centuries to dispose of liquid wastes with the philosophy that the waste was out of sight and out of mind. The recent realization that subsurface waste disposal could contaminate ground water prompted the development of an Underground Injection Control (UIC) program as part of the Safe Drinking Water Act (SDWA) of 1974. This program was designed to prevent contamination of Underground Sources of Drinking Water (USDW) by injection wells. A well, as defined in Title 40 of the Code of Federal Regulations is either a dug hole or a bored, drilled or driven shaft whose depth is greater than its largest surface dimension. Injection is defined as the subsurface emplacement of fluids in a well where a fluid is any material that flows or moves whether it is semisolid, liquid, sludge or gas. No injection is authorized without approval from the appropriate regulatory agency. In states with primacy for implementing the UIC program, this would be a state agency. In states that have not received primacy, the regulatory agency is the USEPA. As part of the UIC program, injection wells were divided into five main classes.

Injection Well Classification

Class I: Wells used to inject hazardous wastes or dispose of industrial and municipal fluids beneath the lowermost USDW.

Class II: Wells used to inject fluids associated with the production of oil and natural gas or fluids/ compounds used for enhanced hydrocarbon recovery. These wells normally inject below the lowermost USDW except in cases where the USDW is hydrocarbon producing.

Class III: Wells which inject fluids for the extraction of minerals.

Class IV: Wells which dispose of hazardous or radioactive wastes into or above a USDW (BANNED).

Class V: Wells not included in the other classes, generally inject nonhazardous fluid into or above a USDW.

If a well does not fit into one of the first four Classes and meets the definition of an injection well, it is considered a Class V well. It should be noted that not all Class V wells are used for disposal. Examples of Class V practices which are not disposal related include Aquifer Recharge, Fossil Fuel Recovery and Mineral Recovery.

Class V - Simple to Complex

Class V injection practices recognized by the USEPA include 30 individual types of wells which range in complexity from simple cesspools which are barely deeper than they are wide to sophisticated geothermal re-injection wells which may be thousands of feet deep. Table 1 illustrates the abundance, geographic distribution, potential for ground water contamination and potential contaminants for the 30 different types of Class V wells.

As can be seen in Table 1, the Class V injection well category is very large and diverse. Class V injection practices can be divided into two general categories, "high-tech" and "low-tech". "Low-tech" wells generally have simple casing designs and surface equipment and inject into shallow formations by gravity flow or low volume pumps. In contrast, "high-tech" wells typically have multiple casing strings, sophisticated well head equipment to control and measure pressure and inject high volumes of fluid into deep saline formations that are separated from aquifers by an impermeable confining layer.

Class V Injection Systems and Your Drinking Water

The majority of Class V injection is into or above the USDW. USDW is defined as an aquifer or its portion which supplies any public water system or contains a sufficient quantity of ground water to supply a public water system, contains less than 10,000 mg/L total dissolved solids and is not an exempted aquifer.

Potential for contaminating ground water is quite varied and depends on:

  1. Where injection occurs relative to the aquifer.
  2. Well construction, design, and operation.
  3. Injectate quality.
  4. Volumes of waste injected.

Wells injecting below the lowermost USDW have the least potential for contaminating ground water. Class V injection directly into USDW is potentially more harmful to the water quality than discharges above the water table. This is because some contaminants are removed from the waste by attenuation, adsorption and degradation in the unsaturated zone.

Based on inventories conducted by the states, it is estimated that there are approximately 170,000 Class V wells in the United States and its Territories and Possessions. This number is only a rough estimate and the actual number may be considerably higher. There are seven main categories of Class V injection wells which contain the 30 individual well types. About 83% of all Class V wells belong to two main categories: drainage wells (57%) and sewage related wells (26%).

Public Awareness: The Key to Protecting Drinking Water

The large numbers of Class V wells releasing a wide variety of contaminants pose a significant threat to ground water supplies. Almost half of the U.S. population receives their drinking water from underground sources. Therefore, it is imperative that these supplies be adequately protected. The threat to ground water from Class V practices can be significantly reduced by utilizing the best management practices available at the local or regional level. One example of a regional practice would be the optimal application of pesticides and fertilizers to reduce the amount of chemicals that would reach ground water through agricultural drainage wells. An example of a local management practice would be a public awareness program to educate people on the detrimental effects of disposing of household chemicals into a septic system. Household chemicals, when discharged into a septic system, can directly contaminate ground water and can reduce the effectiveness of the septic system to remove other potentially harmful contaminants.

Some types of Class V wells may require stricter regulation than those currently in place. The UIC program addresses only a part of the overall threat to underground sources of drinking water. At the local level, a UIC program integrated with careful planning and the utilization of best management practices available and other ground water protection initiatives can significantly reduce the threat to our drinking water supplies.

For additional information you can contact the Tennessee Division of Water Supply at (615) 532-0191 or call the toll free Statewide Environmental Assistance Center number: 1-888-891-8332

For more information regarding Class V well definitions visit EPA’s website