Geoscience Reference
In-Depth Information
TABLE 4.1 Classes of Wells in the EPA UIC Program
Class
Use
I
Injection of hazardous wastes, industrial nonhazardous liquids, or municipal wastewater
beneath the lowermost underground sources of drinking water (USDWs) (650 wells).
II
Injection of brines and other fluids associated with oil and gas production and
hydrocarbons for storage. Injected beneath the lowermost USDW (151,000 wells). a
III
Injection of fluids associated with solution mining of minerals beneath the lowermost USDW
(21,000 wells).
IV
Injection of hazardous or radioactive wastes into or above USDWs. Banned wells unless
authorized by federal or state groundwater remediation project (24 sites).
V
All injection wells not included in Classes I-IV. Generally used to inject nonhazardous fluids
into or above USDWs and typically shallow onsite disposal systems (estimated 400,000-
650,000 wells). b
VI
Inject carbon dioxide (CO 2 ) for long-term storage, also known as geologic sequestration of
CO 2 (estimated 6-10 wells by 2016).
a The table provided by EPA describes Class II wells as “injected below the lowermost USDW.” Although
this is correct in most cases, injection below the lowermost USDW is not required for Class II wells, accord-
ing to UIC regulations.
b Most Class V wells are unsophisticated shallow disposal systems that include storm water drainage
wells, cesspools, and septic system leach fields.
SOURCES: water.epa.gov/type/groundwater/uic/wells.cfm and water.epa.gov/type/groundwater/uic/
class5/classv_study.cfm.
also inject into formations below USDWs, no commercial carbon sequestration facilities
are operating at this time.
Texas, California, and Kansas have the highest number of deep injection wells 4 (count-
ing only Classes I through IV), and 15 states have no deep injection wells at all. Table 4.2
shows the number of UIC wells in each state, listed by well count.
As Table 4.2 shows, Class II injection wells represent 87 percent of the total number of
Class I through Class IV wells. For this reason the oil-producing states of Texas, California,
Kansas, Wyoming, and Oklahoma have higher numbers of deep injection wells than other
states.
States, territories, and tribes can submit an application to the EPA to obtain primary
enforcement responsibility, or “primacy,” to implement the UIC program within their
borders. 5 Agencies that have been granted this authority oversee the injection activities
4 A deep injection well is a well that injects fluid below all underground sources of drinking water.
5 See water.epa.gov/type/groundwater/uic/Primacy.cfm.
 
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