A vulnerability evaluation framework for geological storage of carbon dioxide

Carbon dioxide capture and storage has been identified as one of several approaches with the potential to address climate change. Storage technologies include geologic sequestration, ocean storage, and mineral carbonation. Of these, geological storage (GS), the process of injecting captured carbon dioxide into deep subsurface rock formations for long-term storage, has been identified as the most technically feasible approach. While a large body of literature indicates that GS is a viable technology that can be conducted in a safe manner, it is important that this technology be developed in concert with a comprehensive and systematic approach to ensure the protection of human health and the environment.
With that in mind, the U.S. Environmental Protection Agency developed a Vulnerability Evaluation Framework (VEF) to systematically identify those geologic characteristics and other conditions that could increase the potential for adverse impacts from GS projects. The VEF was developed to provide policymakers, stakeholders, industry, and the public with a transparent framework to evaluate vulnerabilities of GS systems. It is based on a review of available GS literature, applicable technical knowledge, and consultation with experts. The VEF has a number of potential applications, including providing permitting assistance (guidance) to regulators, informing site-specific risk assessments and risk management decisions, identifying potential vulnerabilities that could affect siting decisions and possibly constrain carbon dioxide reservoir capacities, and informing and prioritizing approaches to measurement, monitoring, and verification.
The VEF is focused on the three main parts of GS systems: the injection zone, the confining system, and the carbon dioxide stream. It takes a step-wise approach to evaluating these system attributes and then identifies potential impact categories that should be considered. The VEF first identifies and provides approaches to evaluate key geologic attributes of GS systems that could influence (i.e., increase or decrease) the vulnerability to leakage or pressure changes. It then provides an approach to define the area that should be evaluated for adverse impacts associated with leakage or pressure changes. Finally, the VEF identifies receptors that could be adversely impacted if leakage or pressure changes were to occur. These include receptors within the broad impact categories of human health and welfare, the atmosphere, ecological receptors (e.g., terrestrial and aquatic organisms), surface water and groundwater, and the physical environment. The assessment of vulnerabilities to leakage, pressure changes, and the potential impacts to receptors are described in a series of detailed decision-support flowcharts.