A History Rich in Silver
Since the late 1800s, northern Idaho’s Coeur d’Alene Basin has endured the extraction of millions of tons of ore as prospectors collected the fruitful resources the basin held so plentiful. Known as “The Silver Valley” for its abundant supply of silver, zinc and lead, the basin is historically famous for being one of the largest silver mining districts in the country. The waste build-up from more than a century of mining in the Coeur d’Alene Basin has contributed to the area’s polluted watershed, impacting the surrounding environment and wildlife.
A Settlement for the Superfund Site
The Coeur d’Alene Basin, also named the Bunker Hill Superfund Site, has been on the United State Environmental Protection Agency’s (EPA) National Priorities List since 1983. In 2009, the site made history for being a part of the largest settlement ever granted in EPA history: the $1.7 billion settlement included funding for cleanups across the country, with approximately $494 million granted to the Bunker Hill Superfund Site and Coeur d’Alene Trust for the recovery of wildlife and natural resources.
CDM Smith was awarded an engineering support contract with the Coeur d’Alene Trust in 2012. Our first task was to consolidate approximately 1.5 million cubic yards of mine waste at the East Fork Ninemile Waste Consolidation Area in the basin. We worked closely with the Coeur d’Alene Trust as the engineering, design and construction management consultant to deliver a successful project in compliance with EPA standards.
Cleaning up the Coeur d’Alene Basin
A big challenge was identifying a geographical site capable of handling the construction and remediation actions needed to consolidate the large amount of mine waste in the consolidation area. CDM Smith identified a unique topographic saddle area ideal for reducing the waste consolidation area’s footprint while simultaneously expanding the area’s waste volume capacity by an estimated 50 percent, resulting in a cost savings of more than $17 million. Selecting a strategic waste consolidation area allowed for a sustainable, efficient approach to the design and construction management of the site.
An on-site quarry adjacent to the saddle area provided a supply of clean soil and rock, eliminating importing needs for the construction of the Waste Consolidation Area and resulting in significant cost savings. As a result, 175,000 cubic yards of soil and rock were salvaged from within or adjacent to the Waste Consolidation during the initial construction for future use at the Waste Consolidation Area and other mine reclamation and stream restoration activities within the East Fork Ninemile watershed. Without the quarry and soil salvage at the Waste Consolidation Area, the basin would have imported hundreds of thousands of cubic yards of rock and soil from the nearest rock quarry, an estimated 20 miles away. The close and convenient proximity of the quarry and soil salvage area reduced the project’s costs, transportation impact and overall carbon footprint while meeting the EPA’s green remediation best management practices for mining sites.
The high quality design coupled with the teamwork and leadership with everyone involved has allowed this project to be executed with only minimal/minor changes.
CDM Smith successfully delivered the first phase of this project on-time and within budget. A Project Engineer for the U.S. Army Corps of Engineers commended the team, noting: “I was very impressed with the quality of CDM Smith's design. Projects like this are very complex and are ripe for having unidentified site conditions. The high quality design coupled with the teamwork and leadership with everyone involved has allowed this project to be executed with only minimal/minor changes.”
The cleanup of the East Fork Ninemile watershed is ongoing and expected to be complete in 2022, providing a healthier and more vibrant environment for nearby communities and wildlife. CDM Smith continues to provide engineering support the clean-up.