RICO, Colo. – After last year’s Gold King Mine blowout near Silverton, which dumped 3 million gallons of heavy metals into the Animas River, eyes turned to the Rico Argentine mine.

The long-closed site is on about 80 acres just north of Rico. Its leaking St. Louis Tunnel and pond treatment system sit beside the Dolores River, which provides agricultural and municipal water for 27,000 people in two downstream counties, several towns and the Ute Mountain Ute reservation.

But unlike Gold King Mine, the Rico Argentine Mine has had significant pollution-control systems in place. And more control systems are planned, said Paul Peronard, the Environmental Protection Agency’s cleanup coordinator at the mine.

“Here, we have a great understanding of the mineworks and have controls and monitoring in place, so we know where the pressure is,” Peronard said during a June 29 tour. “Based on that, the risk is pretty low.”

The mine is being reclaimed by Atlantic Richfield Co. under a 2011 Superfund order from the EPA. The reclamation program has four major components: new relief wells, more advanced water treatment, real-time monitoring, and a new waste disposal site.

Construction and drilling have begun on two new relief wells that will help drain the tunnel and prevent a blowout.

Mine and EPA officials estimate there is 1.7 million to 2.2 million gallons of water backed up in the mine. The contaminated water has high concentrations of manganese, zinc, copper, arsenic and cadmium.

The Rico Argentine mine’s workings come together to continuously drain through the collapsed St. Louis tunnel at a base flow of 400-600 gallons per minute, spiking to 1,000 gallons per minute in the spring.

But in the past few years, officials have noticed that the pressure behind the collapsed tunnel has been increasing each spring, which they attribute to silt, which has constricted the flow of the drainage.

Monitoring devices in the mine tunnel give operators real-time data on the elevation of the of backed-up water and the built-up pressure. Currently, the water level in the tunnel is at 8,860 feet elevation from sea level. A level considered dangerous is 8,871 feet.

A siphon in the tunnel has been pulling water out and piping it to the treatment facility. But officials fear that is not enough, so two new horizontal relief wells are being drilled into the tunnel to pump backed-up water to the treatment facility. The new wells and pumps are scheduled to be operational by the end of summer.

“We are currently getting water out of there, but let’s not miss the point of preventing a blowout, so we’re installing big relief wells as a redundant safety factor. If it backs up to a level we don’t want, we can pump it out more efficiently,” Peronard said.

A pilot water-treatment system that uses biological controls is working better than expected and is being scaled up to treat higher volumes of mine drainage year-round.

The Enhanced Wetland Demonstration Treatment System is one of two in the nation and is the only one at such a high elevation.

Water from the mine flows through a series of treatment cells with bio-reactor substrates of sawdust and organic material that use bacteria to break down heavy metals.

The treated mine water then flows through a series of 11 settling ponds before being released into the Dolores River.

“The water treatment plant is designed to handle the variable flows and water temperatures year-round,” Peronard said.

The biological system is preferred over the previous lime treatment system, he said, because the spent substrate matrix only has to be replaced every 5-15 years. It also can operate during winter without on-site management in the avalanche-prone area.

Previously, a lime-tower system was used to drop out heavy metals, but it required more regular management of large volumes of solid wastes.

“The water here needs to be treated forever, so we want to make the costs as low as possible to give the plant longevity and not be a huge money pit,” Peronard said.

A double-lined, solid waste disposal site has been built at the site to permanently store mine wastes from the abandoned lime-treatment system as well as the toxic sludge that is removed from settling ponds. The pit can hold 60,000 cubic yards of waste, and can be expanded to store up to 365,000 cubic yards of waste.

Critical systems are wired to be monitored in real time, and there are live cameras throughout the plant. Mine managers and the EPA are notified remotely about the water level and pressure behind the collapsed tunnel, and on flow rates from the mine into the water treatment facility.

“We get real-time readings that ping us on the conditions,” Peronard said. “It’s an impressive system that continuously tracks and monitors operations.”

If a problem threatens the Dolores River, an automated notification system alerts county and emergency managers, irrigation managers, sheriff departments and irrigators.

And the historic and current monitoring data is, or soon will be, posted on the EPA website.

“If the public wanted to know the elevation of water behind the tunnel, they can look it up,” Peronard said.

As an additional precaution against a blowout, the EPA and Atlantic Richfield are considering building a dam just beyond the St. Louis adit that would be capable of capturing up to 2.2 million gallons of water backed up inside the mine.

“If you did have a catastrophic blowout, the dam would knock everything down right there,” Peronard said.

The plans for the dam are in place, and the EPA will make the decision by the end of the summer on whether it is necessary.

Atlantic Richfield is paying for “99 percent” of the costs of the mitigation and reclamation project at the mine, the EPA said, but total costs were not reported. Eventually, a long-term operator will be contracted to maintain the system, and oversight will be handed off to the Colorado Department of Health and Environment.

The tour gave area water managers confidence that the old mine is being controlled.

“It gives me peace of mind that the are doing a good job with the treatment of water and are planning for larger flows,” said Randy McGuire, water-plant manager for the downstream town of Dolores.

“The redundancies designed into the system raises my confidence level,” said Todd Parisi, emergency operations coordinator for Dolores County.

For documents on the mine cleanup and treatment facility at the Rico-Argentine mine go to bit.ly/eparicomine

jmimiaga@the-journal.com