Carbon Dioxide Capture and Sequestration
Storage Safety and Security
To be a viable climate mitigation option, sequestration of carbon dioxide (CO2) must be safe and secure. Current scientific and technical knowledge, coupled with ongoing project experience, confirms that well-selected, well-designed, and well-managed geologic sequestration sites provide a safe way to permanently sequester CO2.
Proper site selection and careful monitoring are important factors in minimizing and identifying any potential impacts to drinking water, human health, and ecosystems. EPA has put into place a regulatory framework to ensure safe storage of CO2.
Answers to common questions about the safety and security of carbon capture and sequestration (CCS) are provided below. In addition, you can listen to CCS experts talk about the security and safety of geologic sequestration of CO2.
Is carbon dioxide stored in underground caverns?
No. Carbon dioxide (CO2) is compressed into a liquid then injected into solid, but porous rock. These rock formations are located thousands of feet underneath cap rock impermeable to CO2. The CO2 becomes trapped in the pore spaces of the rock. Over time, the CO2 dissolves into the pore water or may be transformed into solid minerals.
Can injected carbon dioxide cause earthquakes?
EPA’s Underground Injection Control (UIC) regulations for Class VI wells helps ensure that CO2 injection activities will not result in significant seismic activity. Geologic sequestration sites will be located in seismically stable, non-volcanic areas. Pressure build-up resulting from CO2 injection could cause minor seismic events, though most of these would be too small to be noticed. See the EPA fact sheet on Underground Injection and Seismic Activity for more information.
Can the injected carbon dioxide leak into underground sources of drinking water?
Proper management of CO2 sequestration sites will reduce the potential risks to the surrounding area and resources posed by CO2 injection and sequestration activities. This management takes into account the four major pathways through which injected fluids can migrate up into underground sources of drinking water (USDWs). The four pathways are:
- The drilled holes (“well bores”) of improperly constructed injection wells
- Improperly plugged deep wells in the injection area
- Transmissive faults or fractures in the surrounding rock formations
- Lateral and upward movement into hydraulically connected USDWs.
Requirements of the UIC Class VI Rule and Subpart RR-Geologic Sequestration of Carbon Dioxide of the Greenhouse Gas Reporting Program require proper management of these sites. EPA’s regulations also provide required actions for remediation in the event of a leak, ensuring minimal impact on human health and the environment in the surrounding area. See the EPA factsheet on Addressing the Drinking Water Risks Associated with Injection for more information.
Could large amounts of carbon dioxide be suddenly released?
No. The locations for geological sequestration sites are selected due to their ability to trap CO2 thousands of feet below the surface, minimizing risks to groundwater or the atmosphere. Natural releases of CO2 have occurred in stratified lakes such as Lake Nyos in Cameroon. Carbon dioxide can also seep up through the soil at active volcanoes, such as Mammoth Mountain in eastern California, or through faults or fractures. Events such as these cannot occur from geologically sequestered CO2 sites. See the EPA factsheet How Do the Class VI Requirements Protect Against a Sudden Release of CO2? for more information.