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TABLE 17.2
U.S. EPA Injection Well Classification System

Well Class Injection Well Description Approximate
Inventory
Class I Inject hazardous wastes beneath the lowermost 500
USDW
Inject industrial nonhazardous liquid beneath the
lowermost USDW
Inject municipal wastewater beneath the lowermost
USDW
Class II Dispose of fluids associated with the production of 147,000
oil and natural gas
Inject fluids for enhanced oil recovery
Inject liquid hydrocarbons for storage
Class III Inject fluids for the extraction of minerals 17,000
Class IV Inject hazardous or radioactive waste into or above a 40
USDW
This activity is banned
These wells can only inject as part of an authorized
clean-up
Class V Wells not included in the other classes 500,000 to >
Inject nonhazardous liquid into or above a USDW 685,000
Source: U.S. EPA, 2002b. With permission.

● Aqueous solutions of pesticides and pharmaceuticals
● Boiler and tank cleanouts

Although a number of toxic and hazardous wastes are acceptable for Class I injection wells, many
wastes or characteristics are restricted or not accepted at all, for example:

● Reactive cyanides
● Reactive sulfides
● Flashpoint (e.g., must be greater than 100°C or 212°F)
● PCBs
● Oil content
● Radioactive wastes
● Shock-sensitive wastes
● Infectious wastes

Class I injection wells are regulated under the SDWA (UIC program) and RCRA Subtitle B (40
CFR 146.11–146.14). Class I injection wells are sited and designed such that they inject below the
lowermost drinking water source with a confining zone situated above the injection zone. Injection
zone reservoirs range in depth from 1700 to over 10,000 ft below the surface (U.S. EPA, 2002a).
There are specific requirements regarding siting, construction, operating, monitoring and testing,
reporting and record keeping, permitting and closure for all Class I wells. The two main categories
of Class I wells are hazardous and nonhazardous waste wells.
Hazardous Waste Injection Wells
Injection of hazardous waste into deep wells began in the United States in the 1960s. The technol-
ogy originated with the oil and gas industry. Approximately 89% of the hazardous waste that is land