But the long-abandoned Argentine Mine Complex near Rico is receiving proper pollution controls to reduce the risk of such an accident, mining officials say.
The St. Louis and Blaine mine tunnels once provided access to a vast network of hard-rock tunnels bored into the Rico Mountains.
Now the tunnels act like drains for snowmelt and rain, which accumulate unnatural levels of heavy metals that has to flow out somewhere.
The mine entrances have collapsed, but the wastewater continues to drain out of them within yards of the Dolores River.
“It’s a hazard we need to pay attention to because the Dolores River supplies water for four towns, and for McPhee Reservoir depended on for irrigation,” said Paul Hollar, emergency manager for Montezuma County.
Mine drainage from St. Louis and Blaine flow through an on-site wastewater treatment system that is working properly, according to the EPA and state mining officials.
Eleven settling ponds remove heavy metals, and the water meets state health standards when it returns to the river.
For the past 15 years, the treatment system has being upgraded and maintained under a cooperative effort by former mine owners Atlantic Richfield Co., the EPA, and the Colorado Division of Reclamation and Mine Safety.
“While you can never be sure what is happening two miles back in these tunnels, we feel the mine entrances are under control,” said Allen Sorenson, project manager and engineer with the state’s inactive mine program.
But it was not always that way.
In 2000, a disaster was narrowly averted after years of disrepair threatened to spill decades-worth heavy-metal sludge into the Dolores River.
Rico officials back then became alarmed when the treatment system was abandoned. Beavers began to build dams clogging culverts between the ponds, and the first two ponds began to overflow directly into the river.
“If the banks fail, the ponds with all that settled mineral waste will be dumped into the river and kill the section through town and downstream,” said Eric Heil, the mayor at the time.
The EPA dispatched emergency crews to shore up the banks, and developed a long-term fix. Liability issues prevented Rico from making repairs.
It was also discovered in 1996 that a concrete plug in the nearby Blaine Tunnel was failing, releasing orange-colored, toxic water directly into Sliver Creek, a tributary of the Dolores River.
The Blaine Tunnel plug is designed to redirect drainage through the St. Louis Tunnel, and into the settling ponds.
In 2013, the Blaine plug was successfully repaired, Sorenson said, at a cost of $350,000.
“The mine entrance was shored up, and diversion structure installed,” he said. “There is no surface discharge out of Blaine.”
The problem with the Gold King mine was that the drainage was backing up more than anyone realized, creating an underground reservoir of wastewater that breached a thin layer of backfill when it was disturbed by EPA contractors.
To monitor whether that is happening at the Rico mines, wells with piezometers that measure water pressure and water level were installed behind the collapsed St. Louis Tunnel.
“Investigating whether they are backing up is ongoing,” Sorenson said. “It is being tracked, and if problems are observed they will be addressed.”
The Blaine Tunnel does not have the piezometers, he said, but it is checked several times a year by inspectors to make sure the diversion structure is working and to monitor flow rates.
Sorenson warned that the nature of underground mine tunnels make them unpredictable, and there are no guarantees a scenario like the Gold King mine won’t happen again.
“It’s a significant issue,” he said. “We eliminate risk to the extent possible, but you can’t rule out what a massive surge of water will do.”
jmimiaga@the-journal.com