A historic mine site in the northern Rocky Mountains is comprised of a number of individual mines. Mining began at the site around 1885 with the discovery of silver-bearing vein deposits. Various mines were operated at the site sporadically through the 20th century, with the last operational in the early 1990s. Environmental monitoring at the site began in the early 1980s and partial reclamation efforts were undertaken by the mine operator in the mid-1990s and early 2000s. When the operator entered bankruptcy, reorganized, and entered into a settlement agreement with the State of Montana, a trust was created to address cleanup responsibilities at the mine property and manage the remediation funds.
Trihydro's project efforts focused on delineation and characterization of metals-impacted waste rock, tailings, sediments, soils, surface water, and groundwater associated with the site. Site characterization activities also included inventorying historical structures and mine workings. Test pits were excavated and monitoring wells installed to evaluate potential waste repository locations. Trihydro’s role included assisting with project coordination, conducting environmental sampling, performing data validation, managing project data, and evaluating data.
Subsequent work at the site has included synoptic sampling events along 10 miles of creek, annual groundwater and seep sampling, borrow material investigations, and conducting a formal repository investigation of the preferred, on-site repository location. The repository investigation entailed georeferencing and evaluating mine maps relative to the repository footprint, excavating test pits to evaluate constructability, and installing borings and collecting rock cores to evaluate bedrock conditions. Trihydro also provided assistance during development and public scoping of an Engineering Evaluation/Cost Analysis (EE/CA).
Trihydro is currently serving as the prime consultant for design, bidding, and construction administration of the onsite repository. This engineered repository is designed to contain approximately 400,000 cubic yards of metals-impacted soils, sediments, tailings, and waste rock. Excavation of the repository base is scheduled for the near future, with waste material excavation, repository loading, and capping to occur in subsequent field seasons.
Trihydro continues to assist in routine groundwater and seep sampling, evaluation of surface and groundwater impacts on-site and downstream of the site, and other tasks that arise as part of the ongoing characterization and reclamation of this historic mine complex.