Legacy Copper Mine Reclamation

Situated in the rugged Cascade Mountains near Lake Chelan, the historic mining village now serves as a seasonal retreat for the Lutheran Church. From 1938 to 1957, it was one of the largest copper mines in the United States, producing 200 million pounds of copper. The client’s goal was to conduct mine reclamation and rehabilitate the old copper mine site. They aimed to promote environmental safety and preserve the surrounding natural habitats.
 
Achieving this goal posed several challenges due to the site’s remote location and complex logistics. As part of a superfund site cleanup, the area was accessible only by barge and U.S. Forest Service roads, which created significant logistical hurdles. Extensive preparations, including road upgrades and bridge installations, were necessary to carry out the Legacy Copper Mine Remediation project.
 
The project faced additional challenges from weather delays, regulatory hurdles, and the complexity of managing a 17-day man-camp rotation. These factors required careful planning and innovative solutions in heavy civil construction to ensure the project’s success.

To access and remediate the former copper mine, our team navigated the mountain terrain using barges and U.S. Forest Service roads. Over six construction seasons, we developed quarry and borrow areas, upgraded roads and infrastructure, and demolished existing mine structures.

Our geotechnical construction efforts involved regrading and capping mine tailings. We rerouted and reconstructed a stream next to the tailings. We also relined and rebuilt Copper Creek, which runs through the tailings before joining Railroad Creek.

Additionally, our team installed a slag-cement-bentonite slurry wall which construction started in early 2014 and was completed mid-2015. The self-hardening slurry wall was a combination of slag-cement-bentonite with depths up to 80 ft over 4,700LF alignment to total 256,000 sf. The wall was installed utilizing a PC800 long reach, a PC1250 long reach and a Koehring 1466 long reach excavator. Challenges included excavation through glacial formations, slowing the set time of the self-hardening slag-cement-bentonite slurry to allow excavation to depth, and ensuring a continuous supply of import product based on weekly barge schedules. A combination of pre-drilling to loosen obstructions with an 8-inch rotary hammer and the use of two cranes and 25,000 lb. chisels to fracture or break obstructions were used prior to and during excavation. The required performance criteria for the self-hardening wall was a maximum permeability of 5 x 10-7 cm/sec and a minimum unconfined compressive strength of 50 psi in 28 days.

Furthermore, we performed jet grout stabilization of the tailings slimes and completed the final grading and capping of the tailings. These geotechnical construction techniques ensured effective environmental remediation and stabilized the site.

Today, the village has transformed into a vibrant retreat that attracts visitors looking to escape urban life. Accessible only by the historic Lady of the Lake ferry or by foot through trails linked to the Pacific Crest Trail, the site offers a peaceful escape in the rugged Cascade Mountains near Lake Chelan.

The successful completion of the Legacy Mine Remediation project has made the area safe and environmentally sustainable. The heavy civil construction and mine reclamation efforts have preserved the natural habitats around the former copper mine site. Additionally, they have ensured the safety of visitors exploring the village and its scenic surroundings, setting a model for superfund site cleanup.

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