Denison Mines’ Wheeler River Project would constitute the first-ever use in Canada of in situ leaching (ISL), to extract uranium from an ore body, and the first attempt anywhere to use “freeze wall” technology to limit contaminant spread from an ISL mine. Our review has identified important gaps and shortcomings in the Environmental Impact Statement and the CNSC Staff Submission recommending licencing of the project related to the proposed ISL/freeze wall process and related issues. Given the magnitude of the uncertainties surrounding this application of both freeze walls and in situ leaching, the failure-ridden history of both technologies, and the potential extent and significance of the impacts of short and long-term failures, this proposal cannot responsibly be approved for licencing.