Project Summary for
French Gulch Acid Mine Drainage

Location: Breckenridge, Colorado

Project Description:
There are several abandoned mine sites in French Gulch. Surface and ground water quality studies conducted by the Colorado Department of Public Health and Environment (CDPHE) and the U.S. Environmental Protection Agency since 1989 demonstrated that most of the heavy metal loading to French Creek is from the inactive Wellington-Oro (W-O) mine and mill complex. The W-O was the largest mining operation in the valley. The W-O underground workings consisted of over twelve miles of tunnels, adits, drifts, stopes and crosscuts. Over (80%) of these workings are below the elevation of French Creek and the groundwater table. Mining ceased in the 1960’s due to the prohibitive expense associated with pumping water from the underground mine. The W-O mill processed ore onsite from 1908 to the 1950’s. Approximately 55,000 cubic yards of mill tailings and 43,000 cubic yards of roaster fines are present and exposed at the ground surface at the W-O site. An unknown quantity of mine waste rock also remains on site and an unknown quantity of dredge tailings remains in the valley floor and French Creek. Surface and ground water flow are potential heavy metal pathways to French Creek from the W-O site. Surface water contamination sources and pathways involve direct runoff of leachate from surface mine waste tailings during spring snowmelt and rainstorm events. Groundwater contamination sources and pathways include drainage from the flooded underground mine workings and seepage of leachate from surface mine waste tailings that eventually enter French Creek by groundwater discharge.

Since 1996, site and regional characterization studies have been conducted by AGS, the State of Colorado, U. S. Geological Survey, U.S. Environmental Protection Agency and the U.S. Bureau of Reclamation. The objectives of these coordinated studies are to (1) determine the relative contributions of metal loading to French Creek from the various sources, (2) identify metal contaminant pathways and fate, (3) establish pre-remediation environmental baseline conditions and (4) design appropriate and cost effective remediation options. The characterization studies include Surface Mine Waste Characterization, Mine Pool Characterization, Surface and Ground Water Quality studies, Continuous Groundwater Level Monitoring, Additional Monitoring Wells, Aquifer Testing, Stable Isotope Tracer studies and a Salt Tracer-Injection study. Preliminary results from the characterization studies indicated: (1) surface mine wastes are not major contributors to metal loading; (2) local percolation and runoff of snowmelt is not a significant transport mechanism for metal loading to French Creek; (3) metal loading from W-O mine water is the major contributor to French Creek; (4) mine water discharge is limited to a graben fault block area between the Bullhide and 11-10 Faults at the W-O site and (5) most metals are transported via groundwater pathways associated with the faults, fractured shale bedrock, mine stoping/workings and the alluvial aquifer.

Completion Date: 2002

Contractor Status: Prime Contractor and Project Manager

Client Contact: Mr. Gary Turlington, Bureau of Reclamation
P.O. Box 25007 (D-8313) Denver Federal Center
Denver, CO 80225-0007