Delineation of Underground Sources of Drinking Water in the San Juan Basin, USA to Support a UIC Class VI Permit Application

Abstract Large‐scale underground storage of CO 2 to mitigate climate change is being implemented around the world; this requires additional planning and protections of water resources around the injection sites. In the USA, CO 2 storage and the protection of underground sources of drinking water (USDW's) for an injection site are regulated by the Environmental Protection Agency through the Underground Injection Control (UIC) Program and implemented through its Class VI well permit. Technical criteria of the permit application includes detailed site characterization where the extent of the lowest USDW's, the direction of groundwater flow within them, and their depth relative to the injection zone must be defined. Here, we support a UIC Class VI permit application for a large‐scale commercial CO 2 storage project within the San Juan Basin. We acquired all publicly available groundwater and produced water data and used ArcGIS Pro and the USGS geologic maps of New Mexico and Colorado to define the areal extent of the lowest USDW's in the area. Results indicate that there are seven formations that qualify as the lowest USDW in the region and that hydrocarbon‐bearing formations which report water production should be reviewed as potential sources of drinking water if not exempt. Because very little literature exists in the analysis of potential USDW's for the Class VI permit application, this study may provide insight for future organizations who intend to apply. Our results will be particularly insightful in oil and gas producing states where production formations also contain large volumes of water.