Safe handling of low-pH mill tailings pore fluids, Moab uranium mill tailings remedial action project.

Ore was processed from 1956 to 1984 at Moab, Utah, USA. Interim cover placement on the tailings pile was completed in 1995 and in 1990 pumping of the water began from wells in the pile to the top of the pile to accelerate dewatering and consolidation. In 2000 a system of vertical band drains or wicks was installed, which penetrated the centre of the tailings pile in a triangular pattern. The wicks were connected to a manifold which allowed gravity drainage to a sump, and a small evaporation pond was constructed for the elimination of collected water. Excavation of the pile in 2010 cut into the wicks, several of which began to discharge pore water with a pH as low as 2.5 and high concentrations of ammonia, U and salts. A project was developed to safely handle the pore water while allowing excavation and conditioning activities to continue. Earthen berms of fine-grained tailings were constructed within the contaminated area near the base of the excavation to contain the pore water. Seven ponds were constructed capable of holding 2 400 000 l while preparations were made to eliminate the water. Groundwater contaminated with ammonia and U is pumped to a 1.6 ha lined pond on top of the tailings pile. The pond promotes evaporation to eliminate the water and acts as temporary storage until trucks withdraw the water and apply it on the tailings pile and roads in the contaminated areas for dust control. By October 2010 the amount of pore water was substantially reduced and most of the ponds were eliminated or consolidated into two ponds containing less than 380 000 l, and little additional pore water was encountered as at June 2011.
Ore was processed from 1956 to 1984 at Moab, Utah, USA. Interim cover placement on the tailings pile was completed in 1995 and in 1990 pumping of the water began from wells in the pile to the top of the pile to accelerate dewatering and consolidation. In 2000 a system of vertical band drains or wicks was installed, which penetrated the centre of the tailings pile in a triangular pattern. The wicks were connected to a manifold which allowed gravity drainage to a sump, and a small evaporation pond was constructed for the elimination of collected water. Excavation of the pile in 2010 cut into the wicks, several of which began to discharge pore water with a pH as low as 2.5 and high concentrations of ammonia, U and salts. A project was developed to safely handle the pore water while allowing excavation and conditioning activities to continue. Earthen berms of fine-grained tailings were constructed within the contaminated area near the base of the excavation to contain the pore water. Seven ponds were constructed capable of holding 2 400 000 l while preparations were made to eliminate the water. Groundwater contaminated with ammonia and U is pumped to a 1.6 ha lined pond on top of the tailings pile. The pond promotes evaporation to eliminate the water and acts as temporary storage until trucks withdraw the water and apply it on the tailings pile and roads in the contaminated areas for dust control. By October 2010 the amount of pore water was substantially reduced and most of the ponds were eliminated or consolidated into two ponds containing less than 380 000 l, and little additional pore water was encountered as at June 2011.