Characterization Of Heavy Metals Pollution Sources Associated Witi-I The Inactive Wellington-Or0 Mine Complex, Summit County Colorado

Abstract

Toxic concentrations of heavy metals have contaminated waters of French Gulch and several miles of the Blue River below the Wellington-Oro mine complex, near Breckenridge, Colorado. The Wellington-Oro mines and mill operated from 1887 until the early 1950’s, developing rich lead-zinc-silver sulphide ores from an extensive underground network of tunnels and drifts on at least eight levels. Five levels below the alluvial gravel aquifer in French Gulch are now flooded. Stream sampling showed water quality meeting class one cold water standards for aquatic life upstream from the mine site, and that toxic amounts of zinc, cadmium, manganese, iron, and copper below the mine site greatly exceed state chronic standards for aquatic life in French Gulch and the receiving Blue River. In an effort to design a Non-Point Source reclamation and water quality improvement project under section 319 of the Clean Water Act, it was necessary to characterize the geologic and hydrologic systems present at the site, as well as identify and quantify the sources of metals contamination emanating from the mine complex. A ground and surface water sampling program was initiated in 1991, followed by detailed site mapping, geophysical surveys, and investigation of historic mine maps and subsurface data. Continued drilling, ground water sampling, mine waste analysis, and interpretation of the bedrock and mine geology eventually revealed the site was far more complex than originally anticipated. Ultimately, four separate sources of metals contamination were identified: 1) Discharge of the mine pool from abandoned shafts constructed through the alluvial aquifer to the stopes and drifts below; 2) Discharge of the mine pool through faults and fractures in the bedrock which are in communication with the mine workings and valley floor of French Gulch; 3) Leaching of metals from mill tailings and roaster waste heaps dumped in and on the gravel aquifer of the valley floor, which are periodically saturated during spring high flow period, then drained during dryer seasons; 4) Storm water runoff from the waste piles, tailings, and roaster heaps which runs directly into the creek. This paper describes key elements necessary to characterize inactive/abandoned mine sites for potential water quality remediation work, illustrating the dangers of plunging ahead with pre-conceived or “off-theshelf’ abatement strategies before an understanding of the geologic, hydrologic, and physical systems governing metals contaminant sources at the site is developed.