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Protecting Groundwater

Put it Back Class VI Wells Protecting Groundwater

Underground Sources of Drinking Water

In the case of Class VI wells, the U.S. Environmental Protection Agency (EPA) is primarily focused on protecting underground sources of drinking water (USDW). To do this, the agency has set forth a number of minimum federal technical criteria to ensure the safety of USDWs before, during, and after a Class VI well operation. Below are some criteria that apply to Class VI wells.¹²

Class VI wells inject CO₂ for long-term storage to reduce emissions to the atmosphere.

Federal Requirements

Site Characterization

Class VI permit applicants must provide extensive information about the local and regional geology and hydrogeology of the proposed site. The purpose of the EPA’s Underground Injection Control (UIC) Program’s evaluation of this information is to inform a determination that the Class VI well will be sited in an area with a suitable geologic system, consisting of an injection zone with sufficient capacity to receive the CO₂ to be injected and a confining zone that is free of transmissive faults or fractures.³

Well Construction

Class VI permit applicants must submit proposed schematics and construction procedures for the injection well. The purpose of the UIC Program’s evaluation of well construction information is to ensure that the injection well will be constructed in a manner that is appropriate to planned operations, is compatible with the CO₂ and subsurface chemistry, and will maintain integrity throughout its duration.⁴

Well Operations

After injection is authorized, the owner or operator will begin to inject CO₂ and perform required testing and monitoring. The information the owner or operator will generate and submit should demonstrate that the project is operating within permitted limits, including that the well maintains mechanical integrity.⁵

Monitoring

The rules require Class VI permit applicants to develop and implement a comprehensive testing and monitoring plan for their projects during the following phases of the project:

Prior to well construction
Prior to operation
During injection
Post injection (end of life)

Monitoring plans are checking for a number of issues, for example: is the CO₂ causing pipe, mechanical or cement corrosion; is there a leak in the well, has groundwater quality been compromised, is the CO₂ fluid tracking within the formation as designed, is there any leakage into surface air and/or soil.⁶

Financial Responsibility

Class VI permit applicants must submit information to demonstrate financial responsibility for corrective action, injection-well plugging, post-injection site care and site closure, and emergency and remedial response. Review of information is important to verify that there is sufficient funding to cover all applicable activities. In addition, review must ensure that, in the event that owners or operators experience financial difficulties, financial resources are available for a third party (i.e., one that is retained by the EPA) to carry out activities related to closing and, if needed, remediate the storage site to ensure that USDWs are not endangered. An important goal is to avoid financial responsibility becoming a burden to the taxpayer.⁷

Well Plugging

Proper plugging of Class VI injection wells is necessary to ensure that the wells do not serve as conduits for fluid movement into USDWs following cessation of injection and site closure. Wells are typically plugged by filling the hole with cement through a carefully engineered process.⁸

Site Closure

After non-endangerment has been demonstrated and approved by the UIC Program Director, the owner or operator closes the site as described in the approved plan and submits a site closure report to the UIC Program Director.⁹

Proper site closure is necessary to ensure that all monitoring wells are plugged appropriately to prevent them from serving as conduits for fluid migration and to restore the Class VI project site for other uses. The documentation associated with site closure is needed to ensure that future land owners and planners will be made aware that CO₂ is stored in the subsurface and help authorities impose appropriate conditions on subsequent drilling activities that may penetrate the injection or confining zone(s).¹⁰

Oklahoma Academic Standards

Environmental Science: 2.6

TEKS Standards

Earth & Space Science: 1.C, 3.D, 11.E, 12.A, 12.D
Earth Systems Science: 1.A, 1.B, 1.F, 1.G, 2.D, 4.A, 4.C, 9.D, 13.A, 13.B
Environmental Systems: 1.A, 1.D, 1.F, 2.D, 4.A, 4.B, 4.C, 6.B, 8.B, 10.A, 12.A, 12.B, 12.E, 13.A
Engineering Science: 4.D, 5.A, 6.A, 6.B
Principles of Applied Engineering: 2.F, 4.D, 5.A, 6.A

College Board Units and Topics

AP Environmental Science: 5.11, 6.5, 7.6, 8.1, 8.2, 8.10

Next Generation Science Standards

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