HYDROGEOLOGIC CHARACTERIZATION OF GROUNDWATERS, MINE POOLS AND THE LEADVILLE MINE DRAIN TUNNEL. LEADVILLE, CO

The Leadville Mining District has been recognized as one of the most intensively mined regions in the world. The district is located in the headwaters of the Arkansas River watershed in the Sawatch Mountains Range in Central Colorado, approximately 120 km southwest of Denver. The 3385 meter long Leadville Mine Drain Tunnel (LMDT) was completed in 1952 to create a free-draining tunnel to dewater existing and future mine workings. 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 and entry into the tunnel is not possible. Roof falls have resulted in blockages which can cause water to pool up, increasing the hydraulic head and presenting a potential blowout problem. Water discharges from the LMDT via the portal and via wells constructed in the tunnel. The LMDT is located within Operable Unit 6 of the California Gulch Superfund site. The US EPA has completed a rigorous hydrogeologic characterization aimed at developing a sound conseptual understanding of the hydrologic, geologic, geochemical and physical conditons that control inflow of ground water and mine pool water to the underground workings associated with the LMDT and the outflow of mine water from these workings. The investigations presented here include hydrogeologic mapping, interpretation of water chemistry data, water level data, time-drawdown test 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 water. These understandings have been used to design a source control system that could be used to control and manage the groundwater intercepted by the LMDT and the mine pools that are conected to the LMDT.