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

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