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Water: Underground Injection Control

Questions and Answers on Using the Class V Experimental Technology Well Classification for Pilot Geologic Sequestration Projects


What is Geologic Sequestration (GS)?
Geologic sequestration, the process of capturing carbon dioxide (CO2) from an emission source (e.g., a power plant) and injecting it into deep subsurface rock formations, is part of a portfolio of technologies and technical approaches (e.g. fuel efficiency measures, use of biomass and alternative fuels, etc.) under consideration for reducing Greenhouse Gas (GHG) emissions to the atmosphere. The U.S. Department of Energy (DOE), through its Regional Carbon Sequestration Partnerships, is sponsoring research at a number of projects that will test the effectiveness and safety of CO2 GS in various geologic settings.

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Why is EPA issuing guidance on CO2 injection?
The purpose of the Guidance is to assist State and EPA regional UIC Program managers and permit writers in evaluating applications for GS projects and writing appropriate and safe permit conditions for these projects.  The Guidance also encourages communication and data sharing to support a nationally consistent management approach, increase understanding of technical issues related to GS, and promote public confidence in an emerging technology with a potentially large-scale application.

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Why are Class V wells being used for GS?
Injection of fluids, including solids, semi-solids, and gases (e.g., CO2) into the subsurface falls under EPA’s authority under the Safe Drinking Water Act (SDWA) to ensure that injection activities do not endanger underground sources of drinking water (USDWs). The UIC regulations address the siting, construction, operation, and closure of injection wells to protect human health and the environment.

The UIC regulations define five classes of injection wells. Of these five classes, EPA has determined that the Class V experimental technology well subclass provides the best mechanism for authorizing pilot GS projects. Class V experimental technology wells are intended to demonstrate unproven but promising technologies. Wells that inject CO2 for the purposes of enhanced oil recovery (EOR) and enhanced gas recovery (EGR) are considered to be Class II injection wells.  While there are similarities between CO2 injection for the purposes of oil and gas extraction and for GS, there are important differences as well. For example, CO2 injection for GS will eventually involve much greater volumes of CO2 which will be stored in the subsurface for very long periods of time. The Class V experimental technology well subclass is the best mechanism for testing the efficacy of CO2 injection for GS, while ensuring an appropriate level of groundwater and public health protection.

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What information does the Guidance contain?
The Guidance provides information for UIC Program managers and permit writers to consider as they evaluate GS project applications and assess the appropriateness of the proposed injection site, the area of review (AoR), and the well’s design and construction. It also provides information for permit writers to consider in writing permit conditions related to mechanical integrity testing (MIT); measuring, monitoring, and verification (MMV); and site closure.

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Who should use the Guidance?
The Guidance will assist UIC Program managers and permit writers in state primacy agencies and EPA Regional direct implementation programs that are responsible for issuing permits for GS projects. GS project operators, including the Regional Carbon Sequestration Partnerships, would find the information in the Guidance useful as they consider injection sites and prepare permit applications.

The Guidance may also be of interest to operators of EOR and EGR wells, state oil and gas boards, and the Interstate Oil and Gas Compact Commission. (Some EOR and EGR operations may be converted for GS when the oil and gas reservoirs are depleted.)  The Guidance also provides information for environmental groups, the public, and interested members of Congress.

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Where can I get additional information?
For further information, or questions relating to the Guidance, please contact Lee Whitehurst, EPA Office of Ground Water and Drinking Water, Drinking Water Protection Division, Prevention Branch, at (202) 564-3896 or Lee Whitehurst (whitehurst.lee@epa.gov).

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