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National Information |
Site Information |
National Priorities List (NPL) HistoryNon-NPL Status |
Superfund Program
French Gulch
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Site Type: Non-NPL City: Breckenridge County: Summit Zip Code: 80424 EPA ID#: COc001093392 Congressional District(s): 02 |
Site Description
The French Gulch site, which includes the former Wellington-Oro Mine, is located approximately 2.2 miles upstream or east of the confluence of French Creek with the Blue River near Breckenridge, Colorado. The area is part of the Breckenridge and Summit county proposed acquisition of the 1,800 acre Golden Horseshoe Open Space.
Extensive underground mining occurred in the valley from the late 1850s to the 1960s. Lode mining recovered lead-zinc-silver sulfide and gold ores from an extensive network of tunnels and adits originating on the steep valley sides. Large floating dredge boats were used to placer-mine the valley floor for gold. The placer dredging disrupted French Creek and its associated alluvial valley material. This resulted in large dredge piles covering the French Gulch valley floor and extending upstream approximately one mile east of the former Wellington-Oro Mine.
Ore veins targeted by the underground mines are commonly associated with faults and fractures that serve as a conduit for groundwater flow. In 1934 the mine workings were reported to consist of more than 12 miles of tunnels. In the 1940s, the present owner, B&B Mines, acquired the Wellington-Oro properties.
Sporadic mining and milling operations occurred at the mine from the late 1940's to the early 1970's. The mine workings remain open and are interconnected with a bedrock fault and fracture system. Since this area contains a large quantity of sulfide-bearing minerals, these conditions promote the formation of acid mine drainage. This is caused by the oxidation of sulfur in the presence of water, forming sulfuric acid in the mine pool water which makes the water acidic. Metals such as cadmium and zinc are soluble in acidic water. As a result, acid mine water flowing through the mine workings becomes highly contaminated with dissolved metals, exits the mine in the form of a seep(s), and enters French Creek. The zinc concentration in the seep water is approximately 5,000 times the concentration in French Creek upstream of the mine and is primarily responsible for the absence of fish populations in the downstream portion of French Creek and a segment of the Blue River.
In 1998, mine wastes including roaster fines, tailings, and waste rock were removed from the mine site to an area with reduced potential for human contact. The materials were capped with impermeable clay and clean gravel. Drainage ditches were installed to reduce infiltration of rain and snow melt into the mining wastes. This material provides little or no contribution to the contamination of French Creek and the Blue River.
Site Risk
| Media Affected | Contaminants | Source of Contamination |
| Water, aquatic species and habitat | Zinc and cadmium | Acid mine drainage from Wellington-Oro mine pool |
Beginning in 1989, EPA conducted numerous investigations into surface wastes, groundwater, surface water, geology, ecology, and precipitation. Surface water and groundwater sampling was initiated in an attempt to determine the source(s) and magnitude of metal contamination present in the water and migration pathways leading to French Creek and the Blue River. Based on data collected from 15 sample locations, the Wellington-Oro Mine Pool was found to be the major contributor of zinc and cadmium load from French Creek into the Blue River.
A natural seep identified as FG-6C is the primary conduit of mine pool water into French Creek. Additional unidentified seeps may also be present. The seep flows year round at an average rate of approximately 100 gallons per minute except during spring runoff when flows have been measured as an average high of 500 gallons per minute. The high metal concentrations of zinc and cadmium in the FG-6C seep water have the greatest effect on aquatic species.
The average cadmium and zinc concentrations at FG-6C are 59 µg/l (micrograms per liter) and 123,000 µg/l, respectively, and are much higher than brown trout can tolerate. The pH of the seep water is 6.4, which is slightly acid (neutral water has a pH of 7). The presence of limestone formations in close proximity to the mine workings adds alkalinity to the groundwater after it has dissolved high levels of metals, thereby neutralizing the high pH in the seep.
Cleanup Progress
In October, 2002, EPA signed an Action Memorandum selecting semi-passive water treatment with settling ponds as the preferred cleanup remedy. The remedy was to treat 300 gallons per minute of water contaminated with zinc and cadmium. The cleanup goal was the following:
Reduce metals loading from French Creek into the Blue River in order to support a sustainable brown trout fishery in the Blue River directly downstream of the confluence with French Creek.
- Improve the water quality in French Creek.
- Limit the concentration of dissolved cadmium and zinc in the Blue River to 4.0 µg/l and 225 µg/l, respectively.
- Limit the concentration of dissolved cadmium and zinc in the Blue River to 4.0 µg/l and 225 µg/l, respectively.
EPA amended the October Action Memorandum based on the adoption of site-specific water quality standards in French Creek and the Blue River and to allow for alternative water treatment technologies. The new proposed alternative while similar to the original would reduce the treatment of contaminated water to150 gallons per minute.
In May, 2003 the Summit Water Quality Committee submitted a Use-Attainability Analysis, Lower French Gulch and the Blue River Downstream from French Gulch near Breckenridge, Summit County, Colorado to the Colorado Water Quality Control Commission. It provided documentation for site specific water quality standards in the Blue River. This study concluded that aquatic habitat in the Blue River was severely impacted by historic dredge mining. Although sections of the Blue River have been restored, habitat is limited to supporting adult brown trout.
The revisions to the water quality standards were approved by the Colorado Water Quality Control Commission on September 8, 2003, and are summarized below:
1) In French Creek, below the Wellington Oro Mine to the confluence with the Blue River are existing water quality conditions since water quality impacts from historic mining could not be reversed.
2) In the Blue River, for approximately 3 miles downstream from the confluence with French Creek, the standard was revised to 4.0 µg/l for cadmium. The zinc standard is based on mineral hardness with a range between 500 to 800 µg/l.
As part of the Town of Breckenridge and Summit County's Golden Horseshoe Open Space Purchase, a settlement was reached that provides for the construction of a water treatment plant at the Wellington Oro Mine. The Wellington Oro Mine was included as part of the 1,800 acres purchased from B & B Mines.
Based on the settlement agreement and the changes to the water quality standards an alternative has been proposed for water treatment which includes the following components:
- Water discharging from the Wellington Oro Mine at seep FG-6C will be collected.
- The collected water will be pumped to the water treatment facility which will be located at the Wellington Oro Mine. The water treatment facility will be designed, constructed and operated by the Town of Breckenridge and Summit County. EPA will oversee the design, construction, and operations. Design and construction are scheduled to be completed in 2006..
- The maximum pumping rate will be 150 gallons per minute. During spring runoff, flows are expected to exceed this pumping rate. It is expected that flows exceeding 150 gallons per minute will bypass the treatment process and flow into the Blue River.
- A physical/chemical process will be used to remove contaminants from the water. The treatment process will be based on cost, performance, reliability, sludge disposal, and operator preferences.
- The effluent water quality discharged is to have a cadmium concentration of less than 4 µg/l and a zinc concentration of less than 225 µg/l. - Solids generated from the treatment process will be separated from the water prior to discharge. The metal sludge generated will be either disposed of into the abandoned mine workings, sold as a metal concentrate, or disposed of into a solid waste landfill.
- The treated water will be discharged into the French Creek watershed.
- A physical barrier will be constructed in French Creek to prevent non-native trout from migrating from the Blue River into upper French Creek.
- This water treatment system will be operated 24 hours per day, 7 days per week until water discharges from FG-6C no longer pose a risk to the environment.
The cleanup remedy will be considered successful if five years after treatment water quality in Segment 2a of the Blue River meets the standards for zinc and cadmium.
Community Involvement
Since the mid 1990's a citizen's advisory group called the French Gulch Remediation Opportunity's Group (FROG) has met to discuss cleanup actions for the Wellington-Oro mine. Over the years the group has been actively involved with EPA and the State of Colorado in identifying cleanup options for French Gulch. Most recently, the group organized an effort to conduct a use attainability analysis in order to modify the standards for French Creek and the Blue River. In addition, the FROG facilitated the acquisition of the property once owned by B&B Mines. The land has been purchased by Summit County and the Town of Breckenridge to be set aside as Open Space. The FROG is no longer meeting since the conclusion of this purchase has resulted in a consent agreement which embodies the clean up goals identified in the amended Action Memorandum. Both the Town of Breckenridge and Summit County will assume responsibility for implementing the clean up of contaminated water from the Wellington-Oro mine site.Site Documents
Contacts
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EPA Victor Ketellapper Libby Faulk |
Colorado Kevin Mackey |
