Characterization of contaminant hydrogeology, French Creek, Breckenridge, Colorado

Most of the heavy metal loading to French Creek is from the inactive Wellington-Oro (W-O) mine and mill complex. 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 the groundwater table. Surface mine spoils consist of mill tailings, roaster fines, and waste rock piles. The characterization studies indicated: (1) surface mine wastes are not major contributors to metal loading; (2) local percolation and runoff of snow melt is not a significant transport mechanism for metals; (3) metal loading from W-O underground mine water is the major contributor; (4) mine water discharge is limited to a graben fault block area between the Bullhide and 11–10 faults; and (5) most metals are transported to French Creek via groundwater pathways associated with the faults, fractured shale bedrock, mine stoping/workings, and the alluvial aquifer.