State and federal officials said today they have determined that a release of contaminated water originating from a mine tunnel at the Captain Jack Mill Superfund site in Boulder County was likely responsible for a fish kill reported Monday in the upper portions of Left Hand Creek.

Field monitoring and the results of water samples collected at various locations along Left Hand Creek by the Colorado Department of Public Health and Environment and the U.S. Environmental Protection Agency have shown that the water coming from the Big Five tunnel was more acidic and contained higher levels of heavy metals than in previous water samples.

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.

The Captain Jack Mill site was added to the Superfund national priorities list Sept. 29, 2003. State and federal authorities have been working to mitigate the impacts of historic mining activities since the cleanup plan, known as a record of decision, was issued in 2008.

A portion of that remedy includes an in-tunnel treatment system to improve the quality of the water flowing out of the Big Five tunnel.

EPA and the state health department, following the reported fish kill on Monday, temporarily closed the flow-through valve on the Big Five tunnel bulkhead and are planning next steps. The agencies will be monitoring the stream water quality over coming days, while continuing to assess the in-tunnel treatment system performance and implementing changes to the system as necessary to improve water quality.

The Left Hand Water District tests both raw and treated water on a continuous basis. The intake remains open following test results that met water quality standards, indicating no potential harm to downstream water users.

Charlie Brennan: 303-473-1327, [email protected] or

Source: The Associated Press

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