MINE MULTI-YEAR RECLAMATION

ENTACT performed environmental remediation and water treatment activities at this high-altitude mine site for more than a decade. Located in a remote area of the Rocky Mountains region at nearly 11,000 feet in elevation, this project presented unique challenges including a short construction season, constrained access and workspace, alpine weather conditions, avalanche hazards, and the logistical limitations of a remote environment. Despite these conditions, ENTACT successfully constructed the first high-altitude wetlands in the world designed to treat acid mine discharge.

Over the years, ENTACT implemented complex remediation and infrastructure improvements at the site, including demolition of derelict mine structures, construction of a flow control structure to manage the potential failure of a collapsed adit, installation of relief wells into the mountainside, and construction of a repository to manage more than 100,000 cubic yards of mine waste. Our work allowed continued water treatment operations during active construction while maintaining protection of the surrounding watershed and local wildlife.

Water treatment wetlands
ENTACT constructed a passive water treatment wetlands system to capture and treat acid mine drainage before discharge to the nearby river watershed. Following construction, ENTACT assisted with system commissioning and constructed a second, larger wetland system and performed upgrades and maintenance. System features included:

• Eight treatment cells, including settling basins and aeration features
• Horizontal and vertical wetlands
• HDPE-liner installed in seven cells
• Monitoring ports and telemetry systems for remote data access and alarms
• Chemical feed and calibration systems for flocculant addition
• Monitoring for hydrogen sulfide gas generation

Expanded constructed wetlands treatment system
ENTACT implemented the Expanded Constructed Wetlands Treatment System (ECWTS), designed to treat up to 1,250 gallons of water per minute. The scope included implementing the ECWTS, developing soil materials from a designated borrow area, and constructing the Calcines Consolidation Area (CCA). On this project, our teams:

• Constructed the CCA foundation, including compaction, piping, rock drains, and geotextile installation
• Excavated 24,000 cubic yards of sediment for consolidation in the CCA
• Excavated 45,000 cubic yards of sediment from two ponds
• Completed grading, access road improvements, and site preparation for ECWTS installation

ENTACT also constructed 18 acres of ECWTS infrastructure across 12 treatment cells, including liners, piping, valving, electrical, and communication systems. The scope also included construction and commissioning of settling basins, a chemical feed building, open channels, maelstrom oxidizers, biocells, aeration cascades, rock drains, and decommissioning of the existing EWD.

Flow control structure
To mitigate the risk of an adit blowout, ENTACT constructed a Flow Control Structure (FCS) capable of holding up to two million gallons of water and releasing it in a controlled manner to existing biotreatment and pond systems. This scope of work included:

• Demolishing the existing portal building and excavating the adit entrance
• Installing stormwater pipe and HDPE piping systems
• Constructing the dam-like gabion FCS using more than 250 gabion baskets and reno mattresses filled with rock
• Installing a slide gate with electric actuator for flow isolation and a telemetry-connected flow meter for remote monitoring

Mine solids repository
ENTACT constructed a lined repository for mine water treatment solids and other mine by-products. The work included relocating the site access road, trenching conduit to relocate overhead utilities underground, and constructing a solids repository partially excavated into the mountainside. Key activities included:

• Regrading steep mountain slopes to meet final design
• Screening excavated material for reuse in road and dike construction
• Installation of HDPE liner, leachate collection system, and drainage layers

Townsite soils project
ENTACT remediated and restored 40 arsenic-impacted residential lots in the nearby townsite area. Work included constructing a geosynthetic clay lined repository, excavating and compacting impacted soils, and maintaining adit water discharge management during construction. For each property, ENTACT prepared individual work plans, erosion control strategies, and traffic management measures. The majority of backfill and repository construction materials were sourced from an on-site borrow area.

Through more than a decade of continuous work at this high-altitude mine, ENTACT restored critical watershed functions, improved long-term water quality through passive and active treatment systems, and stabilized legacy mine waste within a challenging alpine environment.