Denison Mines Corp. announced the successful completion of the inaugural In-Situ Recovery ("ISR") field test program within the the Heldeth Túé uranium deposit ("THT") at the Company's 67.41% owned Waterbury Lake Uranium Project ("Waterbury"), which is located in northern Saskatchewan, Canada and is situated in close proximity to key regional infrastructure, including roads, the provincial power grid, and Denison?s 22.5%-owned McClean Lake mill. The THT ISR field test involved the installation of an 8-well ISR test pattern (?Test Pattern?) designed to collect an extensive database of hydrogeological data, and the program successfully achieved each of its planned objectives, including: Confirmed Hydraulic Conductivity: Pump and injection tests were successfully completed within the Test Pattern, validating hydraulic connectivity in 100% of the test wells within the ore zone, and achieving hydraulic conductivity values (a measure of permeability) consistent with the 2020 Preliminary Economic Assessment (?PEA?) for the project.

Sufficient permeability within the ore zone is a key criteria for the successful deployment of the ISR mining method. Established 10-hour Breakthrough Time with Ion Tracer Test: A subsequent tracer test significantly increased the confidence in the initial hydrogeological evaluations (pump and injection tests) within the Test Pattern. The tracer test demonstrated Denison?s ability to maintain hydraulic control of injected solutions and achieve breakthrough times consistent with expectations.

Demonstrated the Effectiveness of Permeability Enhancement: One method of permeability enhancement was successfully deployed from multiple wells demonstrating the suitability of the method to the THT deposit. Efficiency of permeability enhancement was verified by comparison of pre- and post-permeability enhancement hydraulic testing. The 2023 ISR field test program included preliminary hydrogeological tests completed by using the test wells to move water through the Test Pattern.

Measurements of the movement of water (hydraulic pressure changes) within the ore zone provide evidence of the hydraulic conditions present and are indicative of the potential movement of mining solution in an ISR mining operation. Over 20 different pump, injection, or slug tests were completed during the program. Results from the hydrogeological testing produced hydraulic conductivity values consistent with the PEA.

Importantly, 100% of the wells located within the Test Pattern showed hydraulic connectivity with another test well. Additional supportive test work completed during the program included permeability and porosity tests conducted either downhole or on mineralized drill core recovered during the test program.