Tetra Tech implemented a design-build remediation project for an underground copper mine at the former Rio Tinto Mine in northwest Nevada. The 280-acre Rio Tinto Mine operated from 1932 to 1947, milling low grade ore on-site. Tailings from the milling process were placed in the lower Mill Creek Valley, and half of the tailings were completely saturated with water, which caused downstream migration of contaminants. Tetra Tech transported contaminated mine tailings to a constructed, on-site long-term storage repository.

The team excavated soil from a nearby hillside for the repository. The soil was stockpiled for beneficial reuse as backfill in the tailings pond and construction of the evapotranspirative cover on the repository. This cover includes a series of constructed stormwater terrace channels, which intersect and convey the runoff from the slopes to two perimeter channels or spillways.

Tetra Tech worked to restore the previous mine site to its natural condition before mining activities. The team also restored Mill Creek to facilitate fish passage with the use of fish resting pools and sections of stream riffles.

Over the life of the project, Tetra Tech removed and treated approximately 600,00 cubic yards of tailings, treated 2 million gallons of contaminated mine water, and restored 2,200 feet of Mill Creek with the capability to facilitate fish passage.