Class I

Class I wells are used to inject fluids deep into confined rock formations thousands of feet below Underground Sources of Drinking Water (USDWs). There were several hundred regulated Class I wells in 2018 and about half of them were inspected that year.

2018 Injection Wells by Class

Injection Well ClassNumber of Injection WellsInjection Wells Inspected
Class I830453
Class II181,43184,317
Class III28,327406
Class IV12227
Class V531,1764,038
Class VI20

Source: EPA 816F19005 April 2020

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.1

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.1

In 2018 only 17% of Class I wells disposed of hazardous waste.1

Non-Hazardous Industrial Waste

Non-hazardous industrial waste disposal wells make up 53% of all Class I wells as of 2018. Disposal of non-hazardous industrial water occurs in 19 states including Texas, California, Louisiana, Kansas, and Wyoming.1

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.1  

Radioactive Waste

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


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.1

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.1

The EPA compiled a report on the human health risks associated with Class I UIC wells.

Class I EPA UIC Wells
  1. USEPA. (n.d.). Class I industrial and municipal waste disposal wells. Retrieved 11/9/2020 from

Images: “Graphic” by Top Energy Training