Background information. The Dinero Tunnel, which extends approximately 3,000 feet from the surface to the Dinero Shaft, was used in the late 1800s to mine primarily for silver. In more recent years, the tunnel, located approximately five miles west of Leadville, Colorado, began to discharge acid mine drainage into Sugarloaf Gulch, a tributary to the Lake Fork River which ultimately drains into the upper Arkansas River. Consequently, acid mine drainage from the Dinero Tunnel has significantly affected downstream waters, including a wet meadow and beaver pond complex. Occasionally, the Dinero Tunnel experienced blowouts that developed when temporary pressure would build up behind a blockage in the tunnel, which would then expel sludge [...]
