Mine remediation: New hope for old messes

Posted: Dec 9, 2019

For all their knowledge of the land, miners, whose legacy lives long in Colorado, had little thought of the long-term environmental consequences of their work. For over 150 years, coal, gold, silver, uranium, gypsum and limestone, among other resources, have been drilled, blasted and hauled from their hiding places. When the supplies were exhausted in one spot, the miners simply walked away.

As we now well know, when a mine closes, the story doesn't end there.

There are an estimated 23,000 abandoned mines in Colorado, and many more throughout the West. Since 1980, Colorado’s Inactive Mine Reclamation Program has been the sole body charged with addressing the hazards of abandoned mines. During that time, it has secured the openings of 5,600 mines and reclaimed 1,539 acres of mined land. But the tailings of thousands of defunct mines are still spoiling countless acres and 1,300 miles of streams.abandoned mine colorado

Colorado’s remediation program is limited by the reclamation fees paid by current coal mine operations. Since restoration is time-consuming and costly ($1.5 million per mine by some estimates), only a fraction have been reclaimed.

A much cheaper possible solution, currently being field-tested by a non-profit based in Carbondale, may change the reclamation landscape entirely.

Since 2007, the Flux Farm Foundation has been working on reclamation with a promising substance known as biochar. Biochar is made by burning biomass (like wood, animal and crop waste) in an oxygen-limited environment, resulting in a stable form of carbon that has superior water- and nutrient-retention abilities.

These characteristics make it an ideal candidate to restore moonscape-like mine sites, where vegetation (that could capture toxic metals leaching out of abandoned mines and into waterways) is long gone.

Using biochar to reduce metal toxicity and to boost the fertility of compromised soil isn’t a new concept, but using it to clean up mines is. The Mountain Studies Institute, based in Silverton, has done some small-scale biochar trials on mine lands in the San Juan Mountains, but Flux Farm’s Hope Mine Project is the first time an entire mine has been taken on.

The Hope Mine, near Aspen, is one of Pitkin County’s nearly 800 abandoned mines. After attempting to resurrect the erstwhile silver mine in the early 20th century, it was ditched again when it came up empty. Since then, heavy metals including arsenic, lead, cadmium and zinc have been leaching out of the waste rock, which is scattered around the mine site like guts scooped out of the belly of Aspen Mountain. In several spots the tailings abut Castle Creek, Aspen’s main drinking water supply.

Flux Farm’s Morgan Williams thinks about biochar as creating a natural netting that immobilizes heavy metals and gives the damaged ecosystem a kick-start. “While the char does not permanently bind to heavy metals, metals temporarily adhere to the surface of the biochar, in some cases for a long enough time for the metals to naturally fall victim to chemical degradation into a permanently immobile and non-toxic conglomerate,” he says. Biochar spread out over contaminated rock and soil also retains moisture, allowing vegetation to gain a foothold during the dry months and it speeds seedling germination.

Millions of beetle-killed pines in Colorado provide an abundant supply of biochar. The 1,600 pounds of biochar used at the Hope Mine came from the Biochar Engineering Corporation in Golden.

Last October, a mix of that biochar, compost and native grass seedlings mix was applied to waste rock slopes over 30 degrees (and up to 45 degrees in some places, which was spread by rock climbers). “The Hope Mine was the first time the technology had ever been scaled to meet the reclamation need for the entire mine,” says Williams.

The trial revealed some real-world logistical and materials handling issues, says Williams, but that phase of the project proved that the biochar technique is simpler than conventional reclamation techniques. And much cheaper. “If what we did at the Hope Mine works, i.e. we are able to re-vegetate the slope, keep erosion at bay, and minimize heavy metals from entering the stream, it will have cost roughly 10 to 20 percent of the cost of conventional reclamation,” says Williams.

The overall success of the Hope Mine Project will be measured when the snow melts, by the number of seedlings that emerge.

If they like what they see, Flux Farm wants to replicate the trial at 10 more mine sites in Colorado this year. They’re looking at gold and silver mines, and one uranium mine.

Government agencies are “skeptical and cautious,” about using biochar to heal the land, says Williams. “We do have the full attention of many federal agencies including the BLM, Forest Service, and EPA. They are watching us closely, with many questions and curiosities,” he says.

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