IAI was contracted to remove and dewater silica sand waste from a frozen settling pond at a Woodbury, Minnesota mine, as an immediate means of restoring capacity to the pond.

A 500 feet by 250 feet settling pond was filled with silica sand waste, a byproduct of the silica sand mining and washing process. The pond was filled with sand waste, which needed to be removed before the mine could continue production. IAI used two pumps, powered by hydraulic power packs, to remove the sand from the pond and transfer it to geotextile tubes. Holes were cut in the ice, utilizing a chainsaw, and the pumps were submerged below the ice. One pump was submerged by a gantry crane and the other pump was held by a truck crane from the shore. The sand slurry was pumped and dosed with polymer then transferred to geotextile tubes for dewatering. The weep water that was released from the geotextile tubes was collected and sent back to the pond.

The sand that was removed from the pond was very fine, almost a paint-like consistency. The level of the entire pond was lowered around 3 feet and the level of the sand was lowered about 5 feet during the course of the pumping. The project was completed in 14 days, including mobilization and demobilization, during January 2012.

Project Challenges

This project had a lot of unique challenges that were new to IAI. The biggest was the extreme cold conditions of northern Minnesota in January. Through most of the project, the temperature was below zero Fahrenheit, which is hard on any mechanical equipment, especially the slurry pump. We were working on ice and had to continuously keep the holes in the ice from freezing around the pump. The polymer and polymer make down unit had to be in a shelter to keep them from freezing. If the project was shut down for more than 30 minutes, all the pipes and hoses had to be completely drained to prevent them from freezing.

Every night, everything had to be drained and disconnected to prevent any water from freezing in the lines overnight. The geotextile tube would freeze every night and accumulate 3-4 inches of ice every night, which made it hard to dewater the tube in the morning.