Hydrogeologic Characterization of Ground Waters, Mine Pools and the Leadville Mine Drainage Tunnel, Leadville, Colorado

The 3,385 meter long Leadville Mine Drain Tunnel (LMDT) was completed in 1952 to create a free-draining tunnel to dewater existing and future mine workings in the Leadville Mining District in the Sawatch Mountains of central Colorado. Since 1952 mining has been mostly discontinued in the Leadville district and the physical condition of the LMDT, which discharges approximately 82 l/s, has deteriorated. Roof falls have resulted in blockages which can cause water to pool up, increasing the hydraulic head and presenting a potential blowout problem. Using its’ authority under CERCLA, the US EPA is planning to implement a number of hydraulic and source control elements which are designed to contain and control mine pool water. To support this work the US EPA has completed a rigorous hydrogeologic characterization aimed at developing a sound conceptual understanding of the hydrologic, geologic and geochemical conditions that control inflow of ground water to the underground workings associated with the LMDT and the outflow of mine water from these workings. The investigations discussed here included hydrogeologic mapping, interpretation of water chemistry data, water level data, tunnel tracing and isotopic tracer analysis. The results of this investigation indicate that the LMDT drains only a small volume of mine pool water and a very large volume of regional bedrock and adjacent alluvial ground water. These understandings have been used to design a containment system to control and manage the ground water intercepted by the LMDT and the mine pool(s) that are connected to the LMDT.