Ingineer66, in a comment to the next previous posting, brought attention to the fact that there are all sorts of wells. In particular, he mentioned waste injection wells. Herein, below, is information concerning injection wells - gleaned from the US Environmental Protection Agency's website. If wells bore you to tears, you should be forgiven for moving along without reading further. For those still reading, by following the links for each of the six classes of wells, below, one may find explanations as to how the owners/operators of wells are to protect drinking water sources from pollution.
Side Comment: Considering the history of earthquakes in Colorado that have been ascribed to fracking, I was surprised by the number of such operations I saw being set up along I-25, north of Denver CO, on a recent trip to visit Elder Brother.
What is a Class I well? Class I wells inject hazardous and non-hazardous wastes into deep, isolated rock formations that are thousands of feet below the lowermost USDW.
Class I Wells
Class I Injection Wells - Isolate hazardous, industrial and municipal wastes through deep injection.
Class I wells are used mainly by the following industries:
- Petroleum Refining
- Metal Production
- Chemical Production
- Pharmaceutical Production
- Commercial Disposal
- Food Production
- Municipal Wastewater Treatment
There are approximately 550 Class I wells in the United States. The geology of the Gulf Coast and the Great Lakes area is best suited for these types of wells, and most Class I wells are found in these regions.
What are the types of Class I wells? Class I wells are classified as either hazardous, non-hazardous industrial, municipal, or radioactive depending on the characteristics of the fluid injected. The construction, permitting, operating, and monitoring requirements are more stringent for Class I hazardous wells than for the other types of injection wells.
The four types of Class I wells are:
- Hazardous Waste Disposal Wells. These wells inject hazardous waste, as defined by the Resource Conservation and Recovery Act ( RCRA). Hazardous waste disposal wells are stringently regulated by the Safe Drinking Water Act and RCRA. Most Class I hazardous wells are located at industrial facilities. Only a few Class I wells are at commercial operations that can accept hazardous waste generated offsite. Class I hazardous waste wells operate in 10 states with the majority in Texas and Louisiana. Approximately 22 percent of Class I wells are hazardous waste disposal wells.
- EPA’s Study of the Risks Associated with Class I Underground Injection Wells (PDF) (113 pp, 1MB, About PDF) describes the current Class I UIC Program, the history of Class I injection, and studies of human health risks associated with Class I injection wells, which were conducted for past regulatory efforts and policy documentation.
- Non-Hazardous Industrial Waste Disposal Wells. These wells, which inject non-hazardous industrial waste, operate in 19 states. The majority of these wells are in Texas, Louisiana, Kansas, and Wyoming. Approximately 48 percent of Class I wells inject non-hazardous industrial waste.
- Municipal Wastewater Disposal Wells. These wells are used to inject municipal wastewater in Florida. These injection wells have a large diameter (up to 36 inches) casing and rely on gravity to place fluids underground. Approximately 30 percent of Class I wells are municipal wastewater disposal wells.
- In November 2005, EPA finalized new requirements for Class I Municipal Disposal Wells in Florida.
- Radioactive Waste Disposal Wells. This sub-class of well may be used to inject waste which contains radioactive material below the lowermost formation containing a USDW within one quarter mile of the well bore. There are no known radioactive waste disposal wells operating in the U.S.
What is a Class II well? Class II wells inject fluids associated with oil and natural gas production. Most of the injected fluid is salt water (brine), which is brought to the surface in the process of producing (extracting) oil and gas. In addition, brine and other fluids are injected to enhance (improve) oil and gas production. The approximately 144,000 Class II wells in operation in the United States inject over 2 billion gallons of brine every day. Most oil and gas injection wells are in Texas, California, Oklahoma, and Kansas.
Class II Wells - Inject oil and gas production related wastes. Visit the Class II Wells page to read more about these wells.
What are the types of Class II wells? Three types of Class II injection wells are associated with oil and natural gas production.
- Enhanced Recovery Wells inject brine, water, steam, polymers, or carbon dioxide into oil-bearing formations to recover residual oil and—in some limited applications—natural gas. This is also known as secondary or tertiary recovery. The injected fluid thins (decreases the viscosity) or displaces small amounts of extractable oil and gas, which is then available for recovery. In a typical configuration, a single injection well is surrounded by multiple production wells. Production wells bring oil and gas to the surface; the UIC Program does not regulate wells that are soley used for production. However, EPA does have authority to regulate hydraulic fracturing when diesel fuels are used in fluids or propping agents. During hydraulic fracturing, another enhanced recovery process, a viscous fluid is injected under high pressure until the desired fracturing is achieved, followed by a proppant such as sand. The pressure is then released and the proppant holding the fractures open allows fluid to return to the well. Enhanced recovery wells are the most numerous type of Class II wells, representing as much as 80 percent of the approximately 151,000 Class II wells.
- Disposal Wells inject brines and other fluids associated with the production of oil and natural gas or natural gas storage operations. When oil and gas are produced, brine is also brought to the surface. The brine is segregated from the oil and is then injected into the same underground formation or a similar formation. Class II disposal wells can only be used to dispose of fluids associated with oil and gas production. Disposal wells represent about 20 percent of Class II wells.
- Hydrocarbon Storage Wells inject liquid hydrocarbons in underground formations (such as salt caverns) where they are stored, generally, as part of the U.S. Strategic Petroleum Reserve. There are over 100 liquid hydrocarbon storage wells in operation.
What is a Class III well? Class III wells inject fluids to dissolve and extract minerals such as uranium, salt, copper, and sulfur. More than 50 percent of the salt and 80 percent of the uranium extraction in the United States involves the use of Class III injection wells. There are about 165 mining sites with approximately 18,500 Class III wells in operation across the nation.
Class III Wells - Minimize environmental impacts from solution mining operations. Visit the Class III Wells page to read more about these wells.
What are the types of Class III wells? Class III wells are used to mine uranium, salt, copper, and sulfur.
Uranium in-situ leaching (ISL) is the most common method by which uranium is extracted in the United States. A typical uranium mining operation requires injection, extraction, and monitoring wells. The process includes the following steps: Injection wells are drilled into the formation containing the uranium.
- A solution known as a lixiviant is injected and allowed to remain in contact with the rocks long enough to dissolve the uranium ore.
- When the lixiviant is almost saturated with uranium, the fluid is brought to the surface via a production well.
- At the surface, uranium is separated from the lixiviant.
- The lixiviant is then injected to extract more uranium.
The majority of Class III wells in the United States are uranium ISL wells.
Salt solution mining wells inject clean water to dissolve the salt and the resulting brine (salt water) is pumped to the surface where the salt is extracted. Two methods are used:
- Normal flow, in which water is injected into the well tubing and the saturated fluid is produced through the annulus between the tubing and the casing.
- Bottom injection, in which fluid is injected through the annulus and produced via the tubing.
If the salt is contained in a dome, a single well typically is used. If the salt is contained in multiple, bedded layers, multiple injection wells are used. Salt solution mining wells make up 5 percent of the Class III wells.
- Copper is mined using injection wells only in a few states. A sulfuric acid solution is used to dissolve the copper ore.
- Sulfur may be mined via the Frasch process, in which super-heated steam is injected into the mineral-bearing formation to generate a sulfur solution that can be recovered. Injection wells are not being used to extract sulfur at this time.
What is a Class IV well?
Class IV wells are shallow wells used to inject hazardous or radioactive wastes into or above a geologic formation that contains a USDW. In 1984, EPA banned the use of Class IV injection wells for disposal of hazardous or radioactive waste. Now, these wells may only be operated as part of an EPA- or state-authorized ground water clean-up action. There are about 32 waste clean-up sites with Class IV wells in the United States.
Class V wells are used to inject non-hazardous fluids underground. Most Class V wells are used to dispose of wastes into or above underground sources of drinking water and can pose a threat to ground water quality, if not managed properly. This website provides information on recognizing the different types of Class V wells and the threats they pose. This website also provides information about:
- what you need to do if you own or operate one of these well types;
- how you can protect ground water; and where you can go, and
- who you can talk to if you want additional information.
Most Class V wells are shallow disposal systems that depend on gravity to drain fluids directly in the ground. There are over 20 well subtypes that fall into the Class V category and these wells are used by individuals and businesses to inject a variety of non-hazardous fluids underground. EPA estimates that there are more than 650,000 Class V wells in operation nationwide. Most of these Class V wells are unsophisticated shallow disposal systems that include storm water drainage wells, cesspools, and septic system leach fields. However, the Class V well category also includes more complex wells that are typically deeper and often used at commercial or industrial facilities.
Other more sophisticated Class V well types could include aquifer storage and recovery wells or geothermal electric power wells that are used to inject geothermal fluids extracted from subsurface hydrothermal systems. Complex Class V wells also include wells that are used for pilot geologic sequestration (GS) projects that are experimental in nature. On 12/10/10, the Agency finalized regulations for GS projects. These new regulations include the creation of a new class of well, Class VI. EPA understands that some of the wells permitted as Class V experimental technology wells may no longer be used for experimental purposes.
Following the final rule, Class V wells that are not being used for experimental purposes must be re-permitted as Class VI wells and will be subject to Class VI requirements. Please see the links below for further information.
- CO2 Geologic Sequestration
- Class V Experimental Technology Well Guidance for Pilot Geologic Sequestration Projects (PDF) (UIC Program Guidance #83) (23 pp, 450K, About PDF)
- COMING SOON: Options for Class V Experimental Technology Well Owners and Operators in the Context of the New GS Rule for Long-Term Storage of Carbon Dioxide (Revised UIC Program Guidance 83)
Regardless of the use of a Class V well, owners and operators are responsible for protecting underlying ground water from contamination by the fluids they inject. Ninety percent of America's public water systems draw their water from ground water sources.
Class VI wells are wells used for injection of carbon dioxide (CO2) into underground subsurface rock formations for long-term storage, or geologic sequestration. Geologic sequestration refers to a suite of technologies that may be deployed to reduce CO2 emissions to the atmosphere to help mitigate climate change. (For information about geologic sequestration and climate change, see EPA's Geologic Sequestration and Climate Change pages)