BOULDER, Colo. – Officials with the Colorado Department of Public Health and Environment (CDPHE) and the U.S. Environmental Protection Agency (EPA) said a release of contaminated water from a federal Superfund site in Boulder County likely killed fish in the upper portions of Left Hand Creek.
Officials said field monitoring as well as results of water samples collected at several locations along Left Hand Creek, “indicate the water discharging from the Big Five tunnel was more acidic and contained higher levels of heavy metals than in previous water samples.”
The spill originated from a mine tunnel at the Captain Jack Mill Superfund site, according to CDPHE officials.
“The high acidity and heavy metals, coupled with the seasonal low flows in Left Hand Creek, resulted in water quality impacts approximately five miles below the superfund site,” officials said in a news release.
After reports of the fish kill last Monday, EPA and the state health department temporarily closed the flow-through valve on the Big Five tunnel bulkhead and are planning next steps, the release stated.
CDPHE spokesperson Meghan Hughes said the number of fish killed was in the "low hundreds." She said the discharge from the mine included a "high metal discharge" and the fish died because the metal count was too high for them to survive. Hughes said there is no long-term impact expected to the reservoir below the creek.
Over the next several days, the agencies will be monitoring the stream water quality while continuing to assess the in-tunnel treatment system performance and implementing changes to the system as necessary to improve water quality, health department officials said.
CDPHE officials said water testing met quality standards, showing no impacts to downstream water users.
The Captain Jack Mill site was added to the Superfund national priorities list in 2003, according to officials, who added both the CDPHE and EPA have been working to mitigate impacts of historic mining activities since a clean-up plan was issued in 2008.