Union Minière Pirdop Copper

"Cleaning up Copper Arsenic Wastes"

What's the most effective way to clean a settling pond containing calcium arsenic precipitates (slime) so that it doesn't leach waste materials into the ground and groundwater?

That's the challenge MWH is tackling in Bulgaria on a US $ 6 million Engineering-Procurement-Construction project for Union Minière - the world's leading zinc products manufacturer and the second largest copper products manufacturer.

Union Minière had acquired a majority shareholding in a copper refinery from the Bulgarian Government, and is cleaning up the old smelter site, which suffers from severe environmental liabilities.

The clean-up project - funded in large part through a World Bank loan - includes closing down a 120,000 -square-meter slime pond known locally as the Blue Lagoon. The name comes from the pond's intense blue color. This color is derived from the copper arsenic wastes generated from the copper metallurgical facility's former wastewater neutralization plant.

Project Details

MWH will greatly reduce the slime volume in the pond by using dewatering and consolidation processes. This is partly done by removing more than 500,000 cubic meters of contaminated demolition debris and contaminated soil from the copper smelter and dumping it into the pond.

These materials will displace the slimes ace and/or stabilize the slimes so that a cover can be placed over the waste to eliminate rainwater infiltration. Where required and at those locations where no debris or soil is dumped, vertical drainage will be applied to help dewatering the slime, after which a reinforced geotextile will be installed to act as a basis for further waste dumping.

The cover will consist of a geosynthetic clay liner (GCL), a geocomposite drainage layer, and a vegetative soil layer. This multi-layer cover will avoid future water infiltration into the slime and dumped waste. It will also avoid any leachates from the slime and fill penetrating into the ground and groundwater system.

Overall, the project will help eliminate additional negative environmental impact and provide lifetime stability of the final rehabilitated slime pond area.