PUBLIC HEALTH ASSESSMENT
COBALT, LEMHI COUNTY, IDAHO
The Blackbird Mine Site is an inactive cobalt and copper mine located in Lemhi County, Idaho. Mining activities were conducted at the site intermittently from the early 1900s until 1982. The mining and processing operations created a 12 acre unreclaimed surface pit, underground mining tunnels, and 2 million cubic yards of mine tailings. Currently, the Noranda Mining Company is conducting an EPA ordered removal action at the site to prevent a potential large-scale release of mine tailings from the tailings impoundment on the West Fork Blackbird Creek.
Heavy metals, including arsenic, cobalt, copper, manganese, nickel, and zinc have been released to area surface waters from acid mine drainage and contaminated runoff from site surface deposits (e.g. tailings and waste rock piles) and from mine adits and groundwater seeps. The discharges of metals have severely impacted the aquatic biota of area creeks including Meadow Creek, Big Deer Creek, Bucktail Creek, Blackbird Creek, and to a lesser extent, Panther Creek. Persons who fish Panther Creek below Blackbird Creek or Big Deer Creek could potentially be exposed to heavy metals by eating fish caught in the creek. The significance of this potential exposure pathway cannot be evaluated, however, because the levels of metals in these fish are unknown.
The Blackbird Mine site may pose a public health hazard for persons, such as hikers, campers, or site trespassers, who inadvertently drink water from area creeks impacted by site contaminants, including Blackbird, Meadow, Bucktail, South Fork Big Deer, and Big Deer Creeks. These persons could experience gastrointestinal effects as a result of ingesting heavy metals, such as arsenic, cobalt, copper, iron, and zinc, in the creek waters. However, warning signs which have been posted along Blackbird Creek should discourage persons from drinking water from this creek. Exposure to metals in the other contaminated creeks is less likely since these creeks are located in higher, more remote areas of the site and, as a result, are more difficult to access.
Other persons, such as former mine employees, previous site investigators, recent site workers, forest service personnel, national forest users (e.g., hikers, fisherman), and/or site trespassers, may be exposed to metals 1) in site surface deposits (e.g., tailings, waste rock) through incidental ingestion, inhalation, and skin contact, and 2) in area creeks impacted by the site through skin contact with surface water and sediment. However, the significance of these exposures is either minimal or cannot be determined from currently available information.
Former mine employees and past site workers, including workers involved in the recent diversion channel and spillway construction, were also subject to exposure to metals through inhalation of airborne solids. Exposures were most likely during site activities which generated significant amounts of fugitive dust, such as blasting, drilling, and earthmoving. Although there is insufficient data to determine if adverse health effects occurred from these exposures, ATSDR is recommending that appropriate occupational safety and health practices be utilized to minimize airborne exposure to any current or future on-site workers.
Human exposure to site-related contaminants in groundwater is unlikely since few persons in the
site area use groundwater as a potable water supply and regional transport of groundwater is
The Blackbird Mine Site is located approximately 20 miles southwest of Salmon, Idaho, in Lemhi County within the Salmon National Forest (see Figures 1 and 2). This inactive cobalt and copper mine is in an area of high mountain ridges and deep canyons, and ranges in elevation from 6,600 feet to 8,200 feet. The site covers approximately 830 acres of private patented mining claims and 10,000 acres of unpatented claims. The site is divided by a ridge into two drainage basins: the Big Deer Creek basin to the north (including Bucktail, South Fork Big Deer, and Big Deer Creeks), and the Blackbird Creek basin to the south (including Meadow, West Fork Blackbird, and Blackbird Creeks). Big Deer Creek and Blackbird Creek both discharge into Panther Creek which in turn flows into the Salmon River approximately 20 miles below Big Deer Creek [1,2].
In the late 1800s, the Blackbird Mine area was discovered to contain substantial quantities of mineral resources, including cobalt and copper. Mining of cobalt and copper at the site began in the early 1900s. Since that time, various companies have extracted cobalt and copper at the site from underground shafts and an open surface pit. The most extensive period of production was from 1949 to 1967. The current owner, Noranda Mining Company, has not operated the mine since 1982 [1,2,3].
The mining and processing of cobalt and copper from the area resulted in the creation of approximately a 12-acre unreclaimed surface pit, 10 miles of underground mine workings (tunnels), 4.8 million tons of waste rock, 2 million tons of mine tailings, and numerous mine adits and portals located throughout the site. The open surface pit and associated waste piles are located in the headwaters of Bucktail Creek, a tributary of Big Deer Creek. Waste rock piles, which range in size from several hundred to 2 million cubic yards, and are scattered along several miles of Meadow and Blackbird Creeks near the mine openings from which they were extracted [1,2].
Mine tailings, a by-product of the ore milling processes that were conducted at the site, were originally dumped directly into Blackbird Creek. However, in the early 1950s, an earthen dam was constructed on the West Fork Blackbird Creek, and since then over 2 million cubic yards of tailings have been deposited in the impoundment behind the dam. In addition, periodic spills from breaks in the pipelines that carried the tailings from the mill to the tailings impoundment have resulted in large quantities of tailings being deposited along and into Blackbird Creek .
In 1993, the Noranda Mining Company began an EPA-ordered removal action at the mine tailings impoundment in order to prevent a potentially catastrophic failure of the tailings dam and resulting release of tailings from the impoundment. The removal action involves the construction of a surface diversion channel across the top of the tailings impoundment and slurry wall upstream of the of the impoundment. The surface channel, which is designed for a 500-year storm event, will replace the existing concrete culvert which currently conveys the West Fork Blackbird Creek underneath the impoundment. The existing culvert is badly deteriorated and is inadequate to carry runoff from a major storm event. A complete collapse of the culvert would cause excess water to accumulate behind the tailings impoundment which could jeopardized the stability of the dam. If the dam were to fail, a catastrophic release of tailings (and associated heavy metals) into Blackbird Creek, Panther Creek, and possibly the Salmon River could occur. The surface channel and slurry wall will also help prevent runoff and groundwater from contacting the tailings pile, thereby reducing metal loadings to Blackbird Creek .
Previous investigations have shown elevated levels of heavy metals, including arsenic, cobalt, copper, manganese, nickel and zinc, in mine drainage from underground mine workings and surface runoff from tailings, waste rock, and unprocessed ore. The results of these sampling investigations are discussed in detail in the Environmental Contamination and Other Hazards section of this document. Discharges of these contaminants have adversely impacted fish and other aquatic life in Blackbird, Big Deer, and Panther Creeks. Since 1981, a wastewater treatment plant has treated contaminated mine drainage from several mine adits which previously discharged directly into Blackbird Creek. However, some adits continue to discharge contaminated mine water to site surface waters.
The Blackbird Mine site was proposed for inclusion on the National Priorities List (NPL) in May 1993. Under CERCLA, ATSDR is required to conduct a public health assessment of all sites proposed to the NPL within one year of proposal.
On November 18, 1993, Steve Richardson, Tina Forrester, and Greg Thomas of ATSDR visited the Blackbird Mine site with a representative of the Noranda Mining Company. The following observations were made during the site visit:
- The site is located in a remote, mountainous area and is accessible by a single unpaved forest service road.
- The mine is currently inactive.
- Evidence of past mining activities was widespread through out the site, including mine roads, a surface mining pit, scattered waste rock piles, open mine adits, old mine buildings and equipment, remains of the old ore processing mill, and the large tailings dam and impoundment.
- There are no residences located close to the site. A tavern (the Panther Creek Inn), located at the confluence of Blackbird and Panther Creeks, is the closest occupied dwelling to the site.
- The Cobalt District Ranger Station is located upstream of the site along Panther Creek. At the time of ATSDR's visit, the station was in the process of being closed for the winter.
- The old Cobalt townsite, located on Panther Creek approximately 2 miles downstream of the Panther Creek Inn, consists of several rustic buildings which currently serve as private residences.
- Several houses were noted along Panther Creek downstream of Cobalt.
- Drainage from the old mine, associated tailings and waste rock has coated the Blackbird Creek streambed with orange-red iron deposits.
- The wastewater treatment plant was operating to treat acid mine drainage from the underground mine workings.
- Construction activities for the West Fork Blackbird Creek diversion channel, across the tailings impoundment, and associated spillway were on-going. These activities were scheduled to be completed by spring 1994.
No permanent dwellings are located on the Blackbird Mine site. A temporary construction trailer, which is being used during the on-going removal activities, is the only occupied structure on-site. The closest permanent dwelling to the site is the Panther Creek Inn, a tavern located approximately 5 miles southeast of the mine at the confluence of Blackbird and Panther Creeks. The inn has been occupied year-round in recent times (at least since 1980). Potable water for this facility is reportedly provided by a "sand spike" which is located at the mouth of Blackbird Creek .
The U.S. Forest Service's Cobalt Ranger Station is located approximately 6 miles from the site (as shown in Figure 1) and is occupied on a seasonal basis from May to November. The potable water for this facility is provided by a spring (Dummy Creek) which is upgradient of Blackbird Mine .
The unincorporated town of Cobalt, Idaho, is located about 2 miles downstream on Panther Creek from the confluence of Blackbird Creek (see Figure 1). During the 1950s, this town provided residences for employees of the Blackbird Mine. All buildings owned by Noranda Mining Company were auctioned or otherwise disposed of in 1987. The remaining structures belong to private individuals who lease them from Noranda. The current population of Cobalt is reported to be 13 . At the present time, the water supply for these persons is unknown .
At least two other residences (summer or year-round) are located on Panther Creek downstream of the town of Cobalt. The source of potable water for these residences is unknown, but, nevertheless, is unlikely to be affected by contamination from the Blackbird Mine site [3,4].
The Blackbird Mine site consists of 830 acres of patented mining claims (private land), and approximately 10,000 acres of unpatented mining claims located on National Forest System Lands (public lands) under authority of the 1872 Mining Law. Approximately 2,750 acres of unpatented mining claims have surface rights which rest with the claimant under 30 U.S.C. The surface rights on the remaining unpatented mining claims are administered by the U.S. Bureau of Land Management [3,5].
The majority of the unpatented mining claims and private land are owned by Hannah Mining, Noranda Exploration Inc., and the Blackbird Mining Company. The latter is a limited partnership which consists of both Hannah Mining and Noranda Mining Inc .
The site is located in the Salmon River Mountains within the Northern Rocky Mountain Range in central Idaho. Streams have cut deep canyons through these mountains, creating slopes which are very steep and rocky. Elevations in the area range from 3,000 feet at the Salmon River to peaks of 9,000 feet near the mine itself. The area is characterized by a wet season from November to March (mostly snowfall), and a dry season from July to September .
The eastern boundary of the River of No Return Wilderness, the largest primitive area in the continental United States, is approximately 5 miles northwest of the site. The Bighorn Crags, a popular recreation area, are about 11 miles west of the site [3,5,6].
Natural Resources Use
As previously discussed, the Blackbird Mine site is located within the drainage basins of Blackbird Creek and Bucktail Creek, both of which are tributaries of Panther Creek. However, the majority of the mine complex is located within the Blackbird Creek watershed, which consists of approximately 21 square miles. This creek, with an elevation ranging from 8,000 to 5,000 feet, is characterized by steep slopes. Large portions of the Blackbird Creek watershed have been disturbed as a result of past mining operations . A small reservoir is located on upper Blackbird Creek upstream of the mine. During the past mining operations, this reservoir was used as a potable water supply for the mine employees .
Panther Creek, with a mainstem of 43 miles (elevation 7000 to 3000 feet), has a watershed area of approximately 600 miles. The average annual discharge of the creek is about 300 cubic feet per second (CFS) near the mouth. The typical high flow period is April through June (due to snowmelt) during which flooding and stream scouring are common. The principal use of the creek is recreational (i.e. sport fishing) and agricultural. Portions of the watershed, mainly in the Blackbird and Big Deer Creek drainages, are disturbed as a result of past mining activities and timber operations. Road construction along major portions of the creek and livestock grazing along upper and lower reaches have also disturbed portions of the watershed .
Historically, Panther Creek and its tributaries served as a spawning and nursery area chinook salmon and steelhead trout and as a permanent residence for trout and mountain whitefish. In the 1940s the chinook salmon run began to decline and dropped sharply following development of the Blackbird Mine in 1949. In 1954, extensive fish kills, involving around 200 adult chinook salmon, steelhead, resident trout, and mountain whitefish, reportedly occurred in Panther Creek. The fish kills were believed to have been associated with acid releases from the mine. In 1957, Panther Creek was closed to salmon fishing to preserve the remaining run [3,5].
Studies conducted in the late 1960s and 1970s identified the following game fish in Panther Creek: rainbow trout, brook trout, cutthroat trout, and mountain whitefish. Rainbow trout were found more frequently than any other fish species. No fish were found in Blackbird Creek or Big Deer Creek, and fewer fish were found in Panther Creek below the confluence with Blackbird Creek than above the confluence. In addition, "live box" studies showed that the segment of Panther Creek just below the confluence with Big Deer Creek was extremely lethal to juvenile steelhead. Since the late 1960s, the Idaho Department of Fish and Game has stocked hatchery-reared rainbow trout, steelhead trout, and/or chinook salmon in upper Panther Creek above Blackbird Creek .
Currently, aquatic biota are practically non-existent in Meadow, Blackbird, Bucktail, and South Fork Big Deer Creeks, and biota in Big Deer Creek have been severely damaged. In fact, recent surveys and monitoring have indicated that Blackbird Creek and Big Deer Creek are devoid of fish. Panther Creek has also been damaged downstream of Blackbird Creek, such that few fish use that area. However, above its confluence with Blackbird Creek, Panther Creek supports a significant population of game fish, including rainbow trout. The major factor presently limiting the aquatic biota of these streams is poor water quality resulting primarily from contaminants released from the Blackbird Mine site [3,7].
Water quality in Panther Creek has reportedly improved somewhat in recent years (since the mining operations ceased.) This is likely due in part to actions taken at the site to reduce the amounts of metals released into Blackbird Creek, such as isolating waste rock piles from the creek flow and diversion of several adit discharges to the site's wastewater treatment plant.
Previous reports indicate that if the sources of metals from Blackbird Creek and Big Deer were eliminated, Panther Creek could eventually become habitable again for resident fish (such as salmon and trout). However, the possibility of restoring the salmonid and steel head runs in lower Panther Creek is believed to be limited, especially since the streambed is heavily laden with fine sediment and, as a result, is unsuitable for spawning purposes .
The central Idaho region in which the site is located has relatively diverse wildlife resources due to the wide variety of habitat available. Big game in the area include deer, elk, bighorn sheep, mountain goats, moose, and black bear. Small game and game birds are also quite diverse. Big game wildlife habitat values consist of low quality summer range. No big game winter range is present in the area [3,8].
There were no relevant health outcome data to review for this site. The individual most likely to be impacted by site contaminants is an occasional trespasser. The mining town of Cobalt has been essentially abandoned since the livelihood of the residents was dependent on active mining operations which ended more that 12 years ago.
No public availability session was conducted for the site because of the site's remote location and the fact that few individuals living in the immediate area would be impacted by the site. However, ATSDR contacted the district and state health department, the regional EPA office, and the local forest ranger station to determine if individuals had reported concerns about the site. The forest ranger reported that several years ago, hikers consuming water from Bucktail Creek had been treated for metal poisoning. ATSDR has been unable to find documentation of this reported exposure. No other health concerns regarding the site have been reported.
The Blackbird Mine public health assessment was available for public review and comment at the Salmon Public Library, Salmon, Idaho, for a 30-day period ending October 27, 1994. In addition, the public health assessment was sent to several individuals and organizations for review. No comments were received during the public comment period.