SILVERTON – Plans using a synthetic foam, a passive wetland and even sugarcane are the latest that members of the Animas River Stakeholders Group are considering in the battle against toxic waste coming from abandoned hardrock mines.
The offending mines, near Gladstone, a ghost town north of Silverton, empty up to 800 gallons a minute of iron, cadmium, copper, zinc and aluminum into Cement Creek, a tributary to the Animas River.
The group heard three reports Thursday on processes to manage toxic waste.
Two reports involved treatment of water draining principally from five mines. The other dealt with toxics in waste piles such as mine tailings.
All the treatment methods are test-proven, but their proponents want to expand from experimental to field-ready status.
A limestone treatment operation was used to neutralize the toxins in the past, but was abandoned. The process is expensive and produces sludge that is difficult to dispose of.
A couple of years ago, the stakeholders group, formed in 1994, tested an electro-shock treatment, intended to cause the heavy metals in the effluent to precipitate. But the system didn’t prove its announced merits.
A method used in Peru
On Thursday, Philadelphia-based David Grubb from CH2MHill described the replication of a method discovered in treating mine waste in Peru.
Sugarcane bagasse – the shredded, fibrous leftover from sugar-making – biodegrades when soaked in acidic water to feed naturally found, sulfate-reducing bacteria. This starts a process, the final stage of which are sulfides that precipitate heavy metals.
Bagasse, otherwise, is good only for burning to produce energy or for paper pulp, Grubb said. For mine-waste treatment, bagasse is plentiful, cheap and lasts much longer as bacteria food than straw or wood waste, he said.
“It’s a 100 percent recycled material,” Grubb said.
The process has been adapted to temperate-zone conditions, using Louisiana bagasse, and has been tested for 15 months at the University of Colorado, Boulder.
Grubb thinks the process is ready for field testing.
Eric Kern and Jacob Waples from Golder Associates and Richard Palladino from Aerix Industries talked about how Golder is experimenting with a synthetic foam produced by Aerix that spreads anti-toxic “amendments” through tailing piles to neutralize a toxic pH.
The foam was developed in the 1940s by Mearl Crete as a fire-fighting agent, Palladino said. Aerix bought Mearl Crete in 1999.
Golder experimented with foam in September at a long-ago mine at Carbon Lakes near here, working on a mound of mine waste 35 feet long, 15 feet wide and 8 feet tall.
The goal was to show where and how fast the foam, propelled by compressed air, moved in the waste heap.
“It’s important to get the foam to go where you want,” Kern said. “We want to continue to assess its distribution over a larger test site.”
Brad Florentin from Durango-based AMEC described how a constructed passive wetland can reduce the toxicity of acid mine waste.
AMEC established a wetlands pilot project involving toxic metals for a confidential client in the San Juan Mountains a year ago, Florentin said. The site, at 9,000 feet elevation, is ready for a second year of operation, he said.
Wetlands, which can be constructed to fit the project, have a long history in cold climates, including the Yukon, Florentin said.
“Our pilot test has worked fantastically well in the winter,” Florentin said.
AMEC want to take the pilot project to the next level, Florentin said. There are 33 problem drainages and 24 waste piles in the upper Animas River basin, he said.