ER was awarded a contract for a large scale project to manage and execute all phases of a project involving the shaping and capping of a 16 acre tailings pile known to be a source of acid rock drainage (ARD) contaminating the Upper Arkansas River in Leadville, Colorado. The work required meeting stringent engineering specifications and completing all fieldwork in a single season at the 11,000’ elevation site.
Temporary erosion controls were constructed prior to excavation and re-grading of the tailing pile. A 1,300 linear foot section of the California Gulch, the local seasonal creek located at the base of the tailings, was permanently relocated through excavation of an adjacent channel, lining the channel with natural materials.
The combined use of an excavator, dozer, off-road dump and crawler excavator allowed efficient movement of materials of varying consistencies on varying slopes. Tailings / fill was placed to grade in horizontal lifts with compaction, using a self-propelled sheepsfoot roller. All organic material and rocks larger than three inches in diameter were removed from the top four inches of the final grade, allowing a suitable surface for placement of the Geosynthetic Clay Liner (GCL). The crew re-routed the sewer line, allowing it to run parallel to the tailings piles, replacing the existing sewer line that ran underneath.
The ER crew overcame the challenge of slimes (bacterial decomposed tailings) that impacted compaction of placed materials. The crew used slime wicks to accelerate drying and slimes were solidified with other tailings as encountered and prior to placement in final grade.
The ER crew installed GCL per design specifications, the GCL was positioned to be rolled directly into place, preventing the need for pulling the material once it was unrolled. Once the liner system was installed, the ER crew exercised extreme caution to prevent damage to the liners during placement of the cover soil.
Project challenges included the logistics of working in a high elevation remote area combined with the tight project schedule requiring all work had to be completed in a single short construction season and mandated planning and stringent schedule controls.