Wellfield costs for water in genGEO are adopted from GETEM (Section S3.5.1). A CO 2 wellfield incurs additional costs for a Class VI permit, which is a special regulatory permit required for CO₂ injection wells in the United States. This additional CO₂ cost is for monitoring wells and equipment, when using hydrothermal reservoirs. For exploration, we adopt the GETEM exploration indirect and contingency cost multipliers in genGEO (i.e.