During the milling operations, the mill tailings were slurried to an impoundment that accumulated over time, creating a pile more than 80 feet thick. Excess water from the impoundment infiltrated into underlying soils and ground water. When milling operations ceased, the surface of the tailings pile was stabilized with an interim cover; however, the tailings, particularly in the center of the pile, retained high water content.
To dewater the pile as much as possible, the former site trustee installed a system of 17,000 "wicks" (vertical band drains) that penetrate the tailings.
The vertical band drains provided a pathway for water to more quickly travel out of the pile. Overburden material was added to the top of the pile to provide additional weighting, which helps "squeeze" some of the water through the vertical band drains. A lined evaporation pond located on top of the tailings pile collects the water.
Dewatering the pile reduced the pore water volume in the material. Substantial further reduction is required before it is transported to the Crescent Junction site for permanent disposal. Dewatering also reduced the amount of contamination from the pile that infiltrated into the ground water and ultimately discharged to the Colorado River.
Approximately 1,408,000 gallons of water (tailings pore fluids) had been collected and evaporated from a lined pond located on top of the tailings pile prior to removal of the pond in 2010 during tailings excavation. The recovery of pore fluids had been decreasing as excess pressure from the additional soils of the overburden material dissipated. However, when excavation of the pile cut into the wicks, pore water was able to flow through the exposed band drains. This water, which has a low pH value, was fed to the interim action pond for evaporation.