Class I

Injection Wells and Sustainable Energy Systems Underground Injection Class I

Class I wells are used to inject fluid waste deep into confined rock formations thousands of feet below Underground Sources of Drinking Water (USDWs). There are several hundred regulated Class I wells and about half of them are inspected each year.

Underground Injection Wells by Class

Injection Well Class	Number of Injection Wells	Injection Wells Inspected
Class I	830	453
Class II	181,431	84,317
Class III	28,327	406
Class IV	122	27
Class V	531,176	4,038
Class VI	2	0

Source: EPA¹

Most commonly found in industrial use, Class I wells fall into one of four subcategories.

Hazardous Waste

The strictest regulations apply to hazardous waste disposal wells. Most of these are found at industrial facilities such as petroleum refineries, metal and chemical factories, and pharmaceutical facilities; only a few Class I wells accept hazardous waste generated offsite. These hazardous waste wells operate in 10 states with the majority located in Texas and Louisiana.²

Hazardous waste, as defined by the Resource Conservation and Recovery Act (RCRA), as revised, may be injected in a Class I well if:

Waste has been treated to become non-hazardous, or
The UIC well owner can demonstrate that the waste will remain where it has been placed for as long as it remains hazardous, which has been defined as 10,000 years by regulation.³

Approximately 17% of Class I wells are hazardous waste disposal wells.⁴

Non-Hazardous Industrial Waste

Non-hazardous industrial waste disposal wells make up 53% of all Class I wells. Disposal of non-hazardous industrial water occurs in 19 states including Texas, California, Louisiana, Kansas, and Wyoming.⁵

Municipal Wastewater

The disposal of municipal waste into injection wells occurs exclusively in Florida where 180 Class I wells inject non-hazardous, secondary-treated effluent from domestic wastewater treatment plants.⁶

Radioactive Waste

There are no permitted radioactive waste disposal wells in the United States.

Requirements

The requirements differ slightly between subclasses, but all Class I injection must occur below the lowermost USDW underneath an impermeable caprock which serves to confine the injected fluid. Most injection occurs between 1,700 and 10,000 feet below the USDW.⁷

Additional requirements for Class I wells are:

Every Class I well operates under a permit.
Each permit is valid for up to 10 years.
Owners and operators of Class I wells must meet specific requirements to obtain a permit. These requirements address the siting, construction, operation, monitoring and testing, reporting and record keeping, and closure of Class I wells.⁸

Public law required the U.S. Environmental Protection Agency (EPA) to complete a study of the risks to human health and the environment associated with hazardous waste disposal practices, including Class I wells. The EPA compiled its report on the human health risks associated with Class I UIC wells, concluding that Class I technology ensures safe disposal, protects USDWs, and affords the public and the environment an extremely low level of risk from injection due to the multiple levels of safety features outlined in the study. We include a link to the report below for reference.

Read the EPA Report on Class I Risks

Images: “Graphic” by Top Energy Training

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