On October 22, 2018, at approximately 11:10 am, an incident regarding mine discharge and potential fish impacts to Left Hand Creek in Boulder County, CO was reported to Region 8 response. The incident location was reported near the intersection of Left Hand Canyon Drive and California Gulch Road, less than 1 mile downstream of the Captain Jack Mill Superfund site, Operable Unit 01 (Big Five adit).
After EPA and the Colorado Department of Public Health and Environment were notified on-scene coordinators and contractors collected samples to assist with the investigation. The on-site investigation and water sampling was conducted along Left Hand Creek starting just above the Left Hand Water District intake approximately 15 miles downstream of the at the Captain Jack Mill Site Superfund site.
Field monitoring and the results of water samples collected at various locations along Left Hand Creek indicate the water discharging from the Big Five adit was more acidic and contained higher levels of heavy metals than in previous water samples. The high acidity and heavy metals, coupled with the seasonably low flows in Left Hand Creek, resulted in water quality impacts approximately five miles below the Superfund site.
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 showing no impacts to downstream water users.