Mine Site Characterization and Reclamation Design
Trihydro provided site characterization services, evaluated on-site waste repository locations to encapsulate mine wastes, and supported the waste repository design and construction to address legacy mining impacts at a southwestern Montana mining complex.
Trihydro partnered in the reclamation of a 1,050-acre mining complex in southwestern Montana. 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 activity in the early 1990s. Site investigations and monitoring began in the early 1980s; 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.
Our team focused on delineating and characterizing metals-impacted waste rock, tailings, sediments, soils, surface water, mine water, and groundwater associated with the site. Site characterization activities also included inventorying historical structures and mine workings. Trihydro’s role included assisting with project coordination, conducting environmental sampling, performing data validation, and managing and evaluating project data. We also led a hydrogeochemical evaluation to assess the mine pool and its potential connection with downstream seeps. The results of this evaluation informed decisions regarding long-term monitoring and treatment for metals-impacted seeps.
Later work at the site included conducting synoptic sampling events along 10 miles of creek, groundwater, and seep sampling; performing borrow material investigations; and carrying out a formal repository investigation of the preferred on-site repository location. The repository investigation involved 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 assisted with the development and public scoping of an Engineering Evaluation/Cost Analysis (EE/CA).
We then served as the prime consultant for the design, bidding, and construction administration of the on-site repository. This engineered repository was designed to contain approximately 400,000 cubic yards of metals-impacted soils, sediments, tailings, and waste rock. The cover design incorporated landform grading concepts to blend the facility into the surrounding native landscape. Construction observation included Unmanned Aerial System (UAS) flights to monitor progress and document waste material removal volumes.
