Remediating a Historic Mine Site to Safeguard the Rio Grande

A historic silver mine from the late 1800s is situated in the San Juan Mountains near Creede, Colorado, a small town known for great fishing and river rafting. While the mine stood abandoned for decades, a series of natural tunnel collapses enabled millions of gallons of metal-laden, acidic groundwater to accumulate underground and discharge to the surface. With approximately 350 gallons of the impacted mine water flowing into a Rio Grande River tributary every minute, the U.S. Environmental Protection Agency (EPA) designated the mine as the Nelson Tunnel/Commodore Waste Rock Superfund Site. Beginning in 2009, the EPA selected HDR for a decades-long, multiphase remediation effort focused on controlling the mine flow and remediating the site to environmental standards. We’ve also supported the EPA’s robust community outreach program at a series of public meetings. 

As part of the Superfund process, HDR led preliminary assessments, conducted remedial investigations and feasibility studies, and developed five interim remedial alternatives for EPA consideration to control the flow of mine water. The selected option includes a 1,400-foot bypass tunnel and an engineered plug system to control and potentially treat the contaminated water. 

Since 2023, we’ve designed a new bridge and platform to enable access to the new tunnel portal while preserving the mine's historic integrity. We've also performed investigations, including extensive drilling, tracer studies, water treatment bench and pilot tests, geophysics, and sampling up to two miles underground within rehabilitated sections of the historic mine. 

In 2025, we completed the design for an interim remedy using flow-control structures to manage discharge, reducing the likelihood of a potential 22-million-gallon uncontrolled release of impounded mine water. 

As the project progresses into tunnel construction, we’re serving as the engineer of record, overseeing implementation of the interim remedial design at the Superfund Site and evaluating options to improve water quality at the mine. Protecting the waters of the Rio Grande and providing a safe habitat for key aquatic species preserves the river’s ecosystem and protects a recreational mainstay in the mountains.