The Nelson Tunnel is a National Priorities List (Superfund) site located in the Creede Mining District in Mineral County, Colorado. Schnabel was part of a team hired by the EPA to develop a focused feasibility study to identify and evaluate remedial alternatives to address the threat of a blowout and sudden release of water and sediments that are currently held behind a series of collapses in the Nelson Tunnel.
The tunnel was constructed between 1893 and 1902 to access and dewater the underground mines along the highly productive Amethyst vein and to provide a haulage route for mined ore. The Nelson Tunnel (including the Wooster and Humphries extensions) is approximately two miles long and, as the lowest tunnel constructed along the vein system, functions as a drain for the underground workings that are connected via winzes and raises. The collapsed tunnel portal is located on the west side of West Willow Creek about one mile north of the City of Creede. At present, access to the Nelson Tunnel is through the Commodore 5 Tunnel, which was driven above the Nelson Tunnel to intersect the Amethyst vein complex and allow development of mines farther north.
After a detailed underground site visit with representatives of DRMS, CDPHE, and the EPA, the team developed five alternatives including selective rehabilitation, flow-through bulkheads, and drainage tunnel reconstruction. Each alternative was evaluated for risk, effectiveness, and cost. As part of the evaluation, we researched historical records and prepared a CAD profile of the workings. In 2019–2020, we conducted a Failure Modes and Effects Analysis for the preferred alternative and presented the results to project stakeholders. In 2020, we participated in public meetings about the project in support of an interim record of decision.