Newmont Gold, Idarado Mine, Colorado

MWH provided turnkey management of mine remediation activities at the high elevation Idarado mine with an 80-year history of mining precious and base metals. Waste materials had been disposed of in ponds, lagoons, or waste piles across the property. Some waste materials were acid-generating and were found to be leaching heavy metals (zinc, copper, and lead cadmium).

MWH prepared final designs and permit documents and managed all construction-related activities associated with the remedial action at 10 tailings facilities covering 150 acres, numerous waste rock piles, and portal discharges.

MWH designed the remedial measures for reclamation of each facility, conducted stability analyses and closure plans. During the subsurface investigation, an area was identified where seepage into the tailings produced saturated slimes that would not support conventional earthmoving equipment. A cutoff trench was designed to intercept the seepage and to reduce the amount of water flowing through the acid-generating tailings.

MWH managed construction for the tailing remediation including tailing regrading of approximately 1 million cubic yards as well as construction of over 22,000 feet of lined concrete and geosynthetic surface water diversion channels for the tailing impoundments and subsurface seepage control structures. In conjunction with the construction crews, MWH developed various operational methods for handling or working over the mine waste materials. These included geotextile applications to "bridge" soft areas during tailing impoundment regrading and implementing high altitude/remote access concrete mixing/pouring methods. To evaluate the effectiveness of these source control measures in meeting water quality objectives, MWH also developed a water quality monitoring program.

Because of the high elevations (9,000 – 13,000 feet above sea level) and limited access to much of the areas where the lined channels were constructed, a Sikorsky helicopter was used to airlift in the aggregate and concrete materials. Conventional truck hauling was tried initially; however, the treacherous high-country road conditions along with the road’s limited capacity to support large haul trucks caused significant delays, safety hazards, and truck damage. By airlifting in the materials, what would have taken two months and caused serious delays in the site remediation, was completed in three days. At another site, a backhoe was lowered 1,200 feet off a cliff to install a pipeline.

The Idarado project received the “Heavy Civil Project of the Year” award by the US Association of General Contractors.