The hunt for more water to sustain the Colorado Front Range development boom has driven metro Denver suppliers to try to tap a new source: defunct mountain gold mines.
And proponents say this emerging approach could help fix the West’s long-ignored environmental problem of old mines draining acid metals-laced muck into streams.
Aurora Water officials on Thursday revealed they’re pursuing a $125 million purchase of underground water at the London Mine complex south of Breckenridge. Discharges from that mine for years have contaminated Denver’s and Aurora’s South Park watershed with cancer-causing cadmium and fish-killing zinc.
The deal, if Aurora council members approve it, would give Aurora up to 5,400 acre-feet of fresh water — enough for 30,000 new residents. Aurora Water would pump the water up from an underground reservoir that holds 100,000 acre-feet of water beneath the mine, perched along the Continental Divide, using two 1,000-feet-deep stainless steel wells.
Utility officials reckon that, by lowering the clean water in that reservoir and preventing it from reaching exposed rock in mine tunnels, which creates a sulfuric acid mix that leaches out cadmium and zinc, Aurora could prevent further degradation of streams and fish life.
“We definitely, for future growth, need to acquire water,” Aurora Water director Marshall Brown said Thursday in a Denver Post interview with his team and owners of the mine.
“This is innovative. It is a water supply that historically has not been tapped by water suppliers. The easier supplies are gone. We are left with more difficult supplies,” Brown said.
“It’s an opportunity to take advantage of an available supply — a win-win both for the municipality and for the environment.”
Aurora is doing this at a time when Front Range cities increasingly struggle to secure enough water to sustain people on land classified as semi-arid yet where the population is growing. Aurora’s current population of 365,000 is projected to double by 2040, and city policy requires always having enough water for 50,000 more people. Some south Denver suburbs, such as Castle Rock, remain uncomfortably reliant on underground aquifers that have been depleted by overpumping. Others in the Colorado Springs area face challenges due to U.S. Air Force and industrial contamination of groundwater.
In Colorado, mountains and rivers on the heavily mined western half of the state carry 80 percent of total water. Less than 20 percent of Colorado residents live in the western half. People are concentrated on the eastern side of the mountains, where nature allocated 20 percent of the water.
Denver Water for more than a century has changed the balance by using tunnels to divert water from west to east, moving it under mountains. Aurora Water relies on a similar system to serve a growing urban expanse east of Denver, delivering 50,000 acre-feet of water. Aurora has pioneered advanced water cleaning, building a $250 million treatment plant, and reuse of water discharged below Denver into the South Platte River and blended with mountain water stored in a dozen reservoirs.
Buying up water rights owned by inactive mines marks one of the more creative attempts by a city to meet rising demand. Aurora’s Spinney Mountain Reservoir sits below the London Mine.
Clean groundwater pumped from the natural reservoir beneath the mine would flow through a tunnel around mine workings, which include 70 miles of tunnels, into South Mosquito Creek and the South Platte River before reaching Spinney for storage.
For years, the London Mine has been contaminating water. Located near Alma, west of Fairplay and 16 miles south of Breckenridge, it was a major producer of gold along with silver, lead and zinc from 1874 into the 1940s. It closed in 1991.
It fell into disrepair. Tunnels collapsed. A stream above the mine seeps into the workings, creating toxic muck with cadmium and zinc levels up to 100 times higher than state health water quality limits. Colorado Department of Public Health and Environment officials cited the mine for violating discharge permit limits in 2009, 2011 and 2013. CDPHE and state natural resources officials previously had intervened to to try to stop the contamination by installing a water treatment plant — but it failed. In 2016, CDPHE officials hit the estate of the deceased mine owner with a $1.1 million fine for polluting South Mosquito Creek.
Denver-based MineWater took over the ownership and obligations that year and began work to reduce the pollution. MineWater water president Joe Harrington, who also worked to contain the Gold King Mine disaster after a U.S. Environmental Protection Agency crew triggered a blowout in 2015, said he saw similarities at the London Mine.
“The portal had collapsed. There was water backed up. … Orange water,” Harrington said.
MineWater workers rerouted a flow from behind a concrete bulkhead plug previously installed in the mine, separating water from exposed rock.
“We went into the mine and changed the plumbing,” Harrington said.
By October 2017, concentrations of cadmium and zinc were reduced significantly so that water flowing from the mine helps, rather than hurts, the creek.
But the natural groundwater, if it rises and meets exposed rock in tunnels, could create more acid drainage.
“If we leave the water in the ground, it leads to more pollution,” Harrington said. “Getting the water out of the ground reduces the pollution.”
So MineWater has been working with Aurora.
“The well-pumping is the cure to the problem, not a prescription to address symptoms, but the well-pumping is the cure,” said Todd Lambert, president of C & A Companies, retained by MineWater to help run the project.
Tens of thousands of inactive mines contaminate headwaters of rivers across the western United States. Lambert and Harrington said urban water suppliers elsewhere probably will want to replicate Aurora’s approach. In Colorado, a 200 gallons-per-minute discharge from the Eagle Mine, near Minturn, stands out as one of many where EPA and state agencies long have known about fish-killing contamination but failed to act — due partly to lack of funding.
CDPHE officials on Thursday declined to discuss the London Mine deal. Colorado Department of Natural Resources officials also declined to discuss it.
But “if they have a water right, they may extract the resource,” according to an emailed response that an agency information gatekeeper said could be attributed to Ginny Brannon, director of the agency’s division of reclamation, mining and safety.
State officials didn’t raise any concerns. They say their agency “partners” with others to reduce pollution “and additional partners and funding can always be used to reduce pollution from these large numbers of … inactive mines,” the statement said.
On Monday, Aurora council members, who have discussed the deal with utility officials in an executive session, will consider an initial purchase of 1,400 acre-feet of water for $32 million. That works out to about $22,000 per acre-foot, comparable with what utilities pay to acquire surface water. A second transaction would expand the pumping to extract up to 5,400 acre-feet a year, depending on a state water court determination of what is sustainable.
Money for the deal would come from fees charged to developers of new homes.
