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PROJECTS:  ENVIRONMENTAL REMEDIATION

Mine Reclamation

Forgen has significant experience working under the unique conditions that are often required of mine reclamation projects. We have a team with the ideal blend of capabilities that can only be gained through years of delivering successful mining projects, and has enabled us to develop our Mining Center of Excellence based in Denver, Colorado. Our crews are established and familiar with preconstruction planning (client-specific HSE compliance, fire protection, and other BMPs), cost tracking, scheduling, and earthwork operations. Our mine-specific multi-disciplinary capabilities include site preparation, structure demolition, stream and wetlands restoration, waste rock and tailings regrading, waste rock and tailings cover construction, repository construction and closure, borrow source and quarry development, and site restoration.

LEGACY COPPER MINE RECLAMATION
Chelan, Washington

  • In-water construction of an island during winter month
  • Site access, bridge, USFS road improvements
  • Quarry and borrow source development and operation
  • Diversion and reconstruction of Railroad Creek
  • Reconstruction/lining of Copper Creek
  • Mill and ancillary structure demolition
  • Tailings regrading and capping
  • Slurry cutoff wall construction
  • Installation of more than 4 miles of seep and groundwater collection trenches and piping

This project involved the remediation of a former copper mine on the upper reaches of Lake Chelan. Located deep in the Cascade Mountains, all access to the site is via barge and U.S. Forest Service roads.

Construction included the development of quarry and borrow areas, road and infrastructure upgrades, demolition of mine structures, regrading and capping of mine tailings, rerouting and reconstruction of Railroad Creek (a stream adjacent to the tailings), and the relining and reconstruction of Copper Creek (a stream that transects the tailings before its confluence with Railroad Creek). Work also included installation of a slurry cutoff wall; seep and groundwater collection trenches and piping systems to capture and redirect mine drainage and seepage to an on-site wastewater treatment plant; jet grout stabilization of tailings slimes; and final grading and capping of the tailings.

The primary goal of the project was to mitigate mine impacts and restore the watershed and riparian habitat above Lake Chelan. The former mining village is a seasonal retreat owned and operated by the Lutheran Church, and has also functioned as a crew camp during each of six construction seasons from 2011 to 2016, providing lodging for up to 21 days per rotation.

Forgen performed early actions and preliminary site preparation activities in 2011 in order to improve contractor access to the site, develop borrow sources and other facilities for future work, and construct a project bypass road around Holden Village. This work was designed to accommodate full scale mine reclamation activities and included access road pioneering and USFS road improvements, bridge improvement and replacement, timber removal from select work areas, and SWPPP controls and ecological protection. Access road construction was performed to provide heavy equipment access to key features of work including the slurry wall work pad adjacent to Railroad Creek and the new streambed for the Railroad Creek realignment. USFS 8301 road improvements included widening, safety berm construction, and construction of turnouts along a 10 mile section between the Lucerne Barge Dock and Holden Village to accommodate mobilization and demobilization of heavy equipment and quarry/borrow area crushing and screening equipment to and from the project site.

After the 2011 construction season, Forgen was awarded two subsequent seasons of work, including the construction of a temporary bypass and relocation of nearly a mile of Railroad Creek in 2012 to 2013. Additional scope elements included construction of a new stream channel and restoration of riparian habitat that would stimulate recovery of the fishery; preliminary shaping and lining of the Copper Creek stream channel; quarry development and operations; borrow area development and operations; slurry wall work pad construction; and demolition of the former mill and ancillary structures.

Remedial work from 2014 to 2016 included the installation of a 3,000 lf cement-bentonite slurry cutoff wall to depths of 90 ft between Railroad Creek and the tailings piles; installation of an HDPE groundwater collection trench inside the wall alignment; jet grout stabilization of slimes in the tailings piles; regrading and capping of two waste rock piles and three tailings piles; final reconstruction of Copper Creek; and the construction of an extensive network of collection trenches and piping required to intercept and redirect seeps and groundwater.

SULPHUR CREEK MINING DISTRICT WASTE REMOVAL
Williams, California

  • Reconstruction of Lincoln Creek stream channel
  • Removal of 20,000 cy of mercury-impacted waste rock from six individual mine sites
  • Sensitive location near hot springs attraction with year-round visitors
  • Bat breeding season
  • Hetch Hetchy tribal considerations
  • Rehabilitation/construction of over 3.5 miles of roads in order to reach mine sites
  • Mobilization of two rail car bridges over two miles of active BLM utilizing cranes to pioneer crossings to the repository

The Sulphur Creek Mine Waste Removal project required mitigation of the migration of mine waste containing mercury into Sulphur Creek. The site is located on approximately 465 acres within the Sulphur Creek watershed in Colusa County, California where elevations range from 1,400 to 1,640 ft above sea level. Several of the mine sites were located directly adjacent to Sulphur Creek, which flows continuously from October to June. The six mine sites included calcine tailings, waste rock, mercury enriched soils, ore, miscellaneous waste piles, and mining equipment and structures. An active hot spring was located on the north bank of Sulphur Creek about one mile east of the Central Mine. Because of a study conducted in 2000-2001 concerning the potential ecological and human health impacts of mercury in the Cache Creek watershed, it was determined that the mine remediation approach would focused on site erosion control and material isolation.

Forgen was contracted by Homestake Mining Company to excavate, haul, and place 17,000 cy of material in an on-site repository in order to provide permanent containment for the waste material, preventing it from migrating into the active watershed. The nearby active hot spring required an alternate route for equipment mobilization / demobilization. This road was two miles long and required significant improvement to accommodate heavy equipment including a Komatsu PC 400 excavator, 4,000 gallon water trucks, and two rail car bridges that had to be installed using 20 ton cranes. The entrance to the road was located off Highway 20 and required traffic control approved by Caltrans in order to provide access and egress. Because of the narrow one lane road, the project team developed a radio communication plan for successfully managing heavy equipment traffic. A marker system was also developed that allowed drivers to communicate their road locations over the radio, notifying others of oncoming traffic.

Additional project complexities included the bat breeding season and the resort owner’s request to utilize the site for a personal event. Although this resulted in standby for our equipment and personnel, the project team offered minimized mobilization and demobilization of equipment in order to mitigate cost impacts. The project team also provided a more cost-effective sound barrier technique in order to meet the specifications of the ecological impacts on the bats within the mine sites.