Emergency Release and Fish Kill Occurred

What to know:

In October 2018, Left Hand Creek landowners reported a fish kill up to 10 miles downstream of the Captain Jack Mine. The fish kill was a result of a standard practice emergency mine pool release conducted by the EPA and CDPHE in September 2018. Prior to the release, the bulkhead flow-through valve was shut, and inner mine pool level was rising much faster than anticipated. The excess water needed to be released. Water quality data from the mine pool indicated acceptable conditions to release without treatment. Though unknown at the time, these data were not representative of the entire mine pool water column. Concerning water levels in the inner mine pool combined with apparently acceptable water quality led to an emergency release of mine water into Left Hand Creek. In reality, the mine pool water was highly acidic and laden with toxic metals that caused a fishkill. After this event, a temporary treatment facility was installed to treat the excess mine pool discharge. Sub-surface remediation activities were then halted in order to revise the remedy techniques.

Yellow Boy

Yellow Boy seen in Left Hand Creek downstream of the Captain Jack Mine near Ward, Boulder County, Colorado. Circa October 2018. Source: Longmont Times Call.

Fish Kill

The fish kill was reported on Oct. 22, 2018 by landowners up to 10 miles downstream of the mine. While the emergency release occurred in early Sept., the effects of the toxic mine water were delayed due to a lag in mine water entering the creek and dilution in the creek during reservoir releases.

Water Quality Metrics

These data show water quality metrics monitored downstream of the mine in Left Hand Creek since 2011. Immediately after the release, concentrations of Cadmium, Copper, Zinc and pH all abruptly exceeded acute, chronic, and pH standards for aquatic life. These exceedances likely caused the fish kill.

Treatment Facility

Photo and description by number of the active treatment facility that was in operation from November 2018 through December 2019 at the Big Five Tunnel.