Reliable and cost-effective monitoring will be an important part of making GS a safe, effective, and acceptable method for CO2 control. Monitoring will be required as part of the permitting process for underground injection and will be used for a number of purposes, such as tracking the location of the plume of injected CO2, ensuring that injection and abandoned wells are not leaking, and verifying the quantity of CO2 that has been injected underground. Additionally, depending on site-specific considerations, monitoring may be required to ensure that natural resources, such as groundwater and ecosystems, are protected and that the local population is not exposed to unsafe concentrations of CO2. An overview of various aspects of.