UPDATE | Nov. 19 — As of Sunday, workers have finished repairs on the Big 5 Tunnel transfer pipeline and overflow to the river stopped at 6:22 p.m. The plant has now resumed treating water from the Big Five tunnel.
IDAHO SPRINGS, Colo. — About 8,000 gallons of untreated mine drainage water was released into the Clear Creek from one of the lines bringing water to the Argo Tunnel Water Treatment Facility in Idaho Springs.
The city reached out to the Colorado Department of Public Health and Environment (CDPHE) to alert them of the line breach on Friday.
The CDPHE's Hazardous Materials & Waste Management Division reported that a company had been doing underground boring and accidentally breached the Big 5 Tunnel transfer pipeline, which is under the ground of Colorado Boulevard and 17th Avenue.
After the facilitators of the Argo Tunnel Water Treatment Facility learned about the breach, they shut down the pump to prevent any more mining water release. The CDPHE estimated that 8,000 gallons of untreated water escaped.
The collection system exceeded its capacity for storing water however, so the CDPHE said mine water will continue to discharge into the Clear Creek at a rate of about 18 gallons per minute until repairs are finished.
Plans are in place to repair the line this week, once necessary parts are available.
People who use water downstream of the treatment facility received an emergency notification message on Friday. The CDPHE said it is analyzing water samples to learn about any potential impacts, however there is no increased risk from this release to anybody using the Clear Creek. In addition, the operators of the nearest downstream municipal intake, at Hidden Valley, are monitoring the water and have not seen any changes.
"The mine water discharge may temporarily increase the amount of dissolved metals present in the water, but it likely will not be detectable, due to the volume of water in Clear Creek," the CDPHE said.
The department said measures have been put in place to mitigate the discharge into Clear Creek, but some short-term discharges of Big 5 tunnel mine water have occurred since the treatment plant was constructed.
"When discharges occur, we strive to address them in a timely manner to ensure that human health and the environment continue to be protected," the CDPHE said.
It's not yet clear if the CDPHE will take any action in regards to the company that performed the underground boring.
Background on Argo Mill & Tunnel
The tunnel is the largest single source of metals contamination to Clear Creek, the CDPHE said, and runs from Central City to Idaho Springs. More than 740 pounds of metals are discharged from the Argo Mill and Tunnel every day, as reported by the U.S. Department of Energy's Office of Scientific and Technical Information (OSTI).
The Argo Mill and Tunnel, one of the largest and most well-preserved historic gold mills in the world, is located in Idaho Springs and in the heart of Colorado's gold mining boom, according to its tour website. It processed more than $100 million of gold ore, which is equal to $2.6 trillion in 2020 dollars. An enormous flood in 1943, plus the preparations needed for World War II, caused it to permanently stop operations.
The mill and tunnel acted as a drain for the Clear Creek, which would run through the tunnel, which was contaminated with acidic materials, and continue back into the creek.
While the mill is a museum today, the tunnel is sealed, though water continues to drain from it. However nowadays, this stream goes through the Argo Tunnel Water Treatment Facility before entering the Clear Creek. The facility was completed in 1998 to process the sludge by removing certain chemicals. It can process 700 gallons a minute.
The treatment facility was built at the Argo Tunnel portal and adjacent to the mill, which is on the National Register of Historic Places list. The removed metals are pressed into solid waste and disposed of in a landfill, according to the CDPHE.
A second plant was built in 2015.
The Argo Mill and Tunnel is part of the Central City-Clear Creek Superfund site. The CDPHE is the lead agency for its remediation, but the EPA Superfund Program provides support and input.
Denver7 has reached out to CDPHE for further details. This story will be updated.