Although many mine facilities have implemented environmentally sustainable practices, communities across North America still face the burden of dealing with impacts from their industrialized past. New wastewater treatment technology being used in Breckenridge, Colorado is allowing this forward-thinking community to counter the debilitating effects of acid mine drainage to reclaim parkland for use in recreation, and discharge clean water that supports local fish populations.
Wellington Oro Mine
From the late 1880s to the early 1970s the Wellington Oro Mine site, located three miles from the Town of Breckenridge, produced silver, gold, lead and zinc from an extensive network of underground tunnels. The largest mine in Summit County, Colorado, it was closed down in 1972, but left in its wake a legacy of zinc and cadmium-laden contaminated water. High levels of this contaminated “acid mine drainage” drained from the miles of abandoned tunnels into a local river system impacting local fish populations.
Breckenridge has become a popular ski resort and recreational playground, where an appreciation of the environment runs deeply among the community’s population. The water from the closed mine site was a source of concern, and prompted a cooperative effort involving three levels of government.
In 2005, the town and Summit County purchased the 1,800 acre site as part of a plan to create an open space to enhance the region’s public amenities. At the same time, they worked with the US EPA and the Colorado Department of Health and Environment to find a system for suitable water treatment to remove the dissolved metals emanating from the abandoned mine site into the Blue River downstream of French Creek. The water would need to meet Colorado Water Quality Standards, as well as protect the nearby brown trout fishery.
Challenge and solution
Although no longer in operation, toxic runoff from the mine is created when rainfall or snow melt enters the mine’s 12 miles of tunnels and crosscuts. As the water moves through the Wellington Oro Mine site it becomes acidic and dissolves zinc and cadmium found in the mine.
Acid mine drainage is a naturally occurring process that happens at an estimated 70 per cent of the world’s mines. Mining activity can expose rock containing sulphide-based minerals in open pits or underground that, when exposed to water, oxygen and common bacteria, creates acidic water that dissolves residual metals in the mine’s rock.
After an international call to action, the community commissioned a 3,200 sq. ft. water treatment plant with the capacity to process over 150 gallons per minute, or up to 80 million gallons of water a year (equivalent to 120 Olympic-sized swimming pools). The treatment facility uses a process called “sulphide precipitation” in order to return to the French Gulch basin clean water with less than 225 parts per billion (ppb) of zinc and 4 ppb of cadmium, meeting the strict criteria set down by Colorado Water Quality Standards. Prior to treatment the average zinc and cadmium concentrations in the untreated water was 270,000 ppb and 112 parts per billion, respectively, concentrations too high to be tolerable to the local brown trout.
In the sulphide precipitation process, the contaminated water is collected in an underground tank and pumped into the plant, where the water chemistry is adjusted using sulphide. The changes in water chemistry cause the dissolved metals to precipitate and form solid metal particles that are recovered using a clarifier and filter. The remaining clean water is then safely released into the French Creek tributary of the Blue River.
Managed by the Town of Breckenridge Water Division, the treatment plant removes about 4,000 pounds of metal a month and meets strict international ISO 14001 standards for environmental compliance. The alternative process considered was “lime treatment”, which would have created a metal sludge requiring specialized disposal and storage. The sulphide precipitation process used by Breckenridge and Summit County instead produces clean, treated water and separated, saleable zinc-cadmium sulphide that can be recycled into useful products.
This unique project, undertaken by three levels of governments, is not only meeting the concerns for addressing water quality, but is allowing this community to reclaim, in perpetuity, a large portion of land that can be protected for public recreation, natural resource protection and as a scenic backdrop. By recovering salable, recyclable metal that can help offset the cost of treatment this innovative plant has been able to leverage advanced technology in order to achieve the community’s goals for sustainability.
Written by Brad Marchant, CEO of BioteQ Environmental Technologies in Vancouver, BC. Contact Brad at firstname.lastname@example.org