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As a result, minimizing CO2 emissions continues to top the list of GHG goals to fight climate change and government and industry now see permanent storage of CO2 in underground injection wells as a viable way to effectively manage emissions right now. This practice, called carbon capture and sequestration (CSS), is particularly promising for large emitters, and the Environmental Protection Agency (EPA) estimates use of CSS by power plants burning fossil fuels could reduce CO2 emissions by as much as 80-90%. For example, assuming a 500 MW power plant emitting about three million tons of CO2 per year and a 90% reduction in emissions, the result would be equal to planting more than 62 million trees that naturally reduce atmospheric CO2 and eliminating electricity-related emissions from more than 300,000 homes annually.
But CSS is not as simple as it might seem because only certain geologic sites can safely and securely store CO2 over the long term, without threatening resources like drinking water supplies. In general, the injection sites are a mile or more underground and are composed of solid but porous rock formations (e.g., sandstone, shale, dolomite, basalt, or deep coal seams) located under one or more layers of cap rock that traps the CO2 and prevents upward migration. The EPA constantly monitors the sites to ensure that the injected CO2 does not escape and remains securely in place. Over time, the sequestered CO2 dissolves into pore water or it may become transformed into solid minerals.
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The U.S. Department of Energy (DOE) estimates the United States has the geologic potential to store between 1,800 and 20,000 billion metric tons of CO2 in underground wells, which is equivalent to 600 to 6,700 years of emissions from large stationary sources at current levels.
On the regulatory front, the original CSS final rules promulgated in 2010 established a new class of injection wells called Class VI wells for CSS under the Safe Drinking Water Act (SDWA) and GHG reporting requirements to track the amount of CO2 sequestered. More recently, in late 2013, EPA took additional action to further protect drinking water and to help relieve some of the regulatory burden on facilities that use or would like to use CSS to reduce CO2 emissions.
In the first action, EPA published guidance regarding the use of Class II wells formerly used in oil and gas production as carbon sequestration wells and clarifies how permitting agencies should determine the need for Class VI permits on a case-by-case basis. In the second action, EPA promulgated a new rule that effectively excludes sequestered CO2 from the definition of hazardous waste under the Resource Conservation and Recovery Act (RCRA). The rule requires facilities to meet other requirements including compliance with U.S. Department of Transportation (DOT) regulations pertaining to off-site shipping of CO2 via pipelines under the Pipeline and Hazardous Materials Safety Administration (PHMSA), Class VI regulations under the SDWA, the stipulation that the injected CO2 stream not contain any other hazardous wastes, and that generators and Class VI operators claiming the RCRA exclusion sign a statement certifying that they have met all the conditions.
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Also in 2013, the United States Geological Survey’s (USGS) methodology for assessing CO2 storage potential for geologic sequestration was endorsed by the International Energy Agency (IEA) as a best practice for determining country-wide storage potential. The USGS released its first national assessment of technically accessible geologic CO2 storage potential in June of 2013 and concluded the United States has a mean of 3,000 metric gigatons of CO2 storage potential in geologic basins nationwide. Links to the assessment are available at http://www.usgs.gov/newsroom/article.asp?ID=3628#.Ut_s6qwo7mJ.