PUBLIC HEALTH ASSESSMENT
BLACKBIRD MINE ENVIRONMENTAL
COBALT, LEMHI COUNTY, IDAHO
This section of the public health assessment describes previous environmental sampling conducted at the Blackbird Mine site and identifies contaminants of concern found in specific site media.
ATSDR selects contaminants of concern based upon the following:
It is emphasized that identification of a contaminant of concern in this section does not mean that exposure to it will cause adverse health effects. Instead, the selected contaminants are those that will be evaluated further in subsequent sections of the public health assessment.
The data tables presented in this section include the following abbreviations and/or acronyms:
EMEG = Environmental Media Evaluation Guide RMEG = Reference dose-based Media Evaluation Guide LTHA = Lifetime Health Advisory MCL = Maximum Contaminant Level MCLG = Maximum Contaminant Level Goal ND = not detected ppm = parts per million (mg/L water or mg/kg soil) ppb = parts per billion (ug/L water or ug/kg soil) mg/kg = milligram per kilogram ug/L = microgram per liter
Comparison values for ATSDR public health assessments are media-specific concentrations that are used to select environmental contaminants for further evaluation. These values include Environmental Media Evaluation Guides (EMEGs), Reference dose-based Media Evaluation Guides (RMEGs), Cancer Risk Evaluation Guides (CREGs), and other relevant guidelines.
EMEGs are media-specific screening values derived by ATSDR from ATSDR minimal risk levels (MRLs), while RMEGs are derived from EPA reference doses (RfDs). ATSDR MRLs and EPA RfDs are estimates of daily exposure to a contaminant that are unlikely to cause adverse, non-carcinogenic health effects.
CREGS are media-specific screening values derived by ATSDR from EPA cancer slope factors. CREGs represent estimated contaminant concentrations based on one excess cancer in a million persons exposed to that contaminant over a lifetime.
Lifetime Health Advisories (LTHAs), which are derived by EPA, represent the level of a contaminant in drinking water (with a margin of safety) at which adverse, non-carcinogenic health effects would not be anticipated during a lifetime (70 years) exposure.
Maximum Contaminant Levels (MCLs) represent contaminant concentrations that EPA deems protective of public health (considering the availability and economics of water treatment technology) over a lifetime (70 years) at an exposure rate of two liters per day.
Maximum Contaminant Level Goals (MCLGs) are drinking water health goals set by EPA at
levels at which no known or anticipated adverse human health effect occurs and which allows an
adequate margin of safety. When there is no safe level for a contaminant, the MCLG is set at
zero. While MCLs are enforceable, regulatory concentrations, MCLGs are not.
A. Environmental
Numerous investigations regarding the sources, fate, and impacts of hazardous substances released from the Blackbird Mine site have been conducted since the late 1960s. Major investigations include those by the U.S. Forest Service; the University of Idaho; Environmental Research and Technology; Noranda Mining Inc.; the U.S. Department of Energy; the Idaho Division of Environmental Quality; and RCG/Hagler, Bailly, Inc.; and Ecology and Environment Inc. The results of these studies are discussed below.
Note: ATSDR has not attempted to differentiate between "on-site" and "off-site" contamination in this public health assessment because 1) exact site boundaries could not be determined from available information; 2) wastes from past site operations have been deposited outside the areas where mining and ore processing activities occurred (e.g., tailings impounded on West Fork Blackbird Creek); 3) contaminants from the site have impacted surface waters far downstream of the actual site (such as Panther Creek), and 4) the exact location where samples were collected could not be determined in some cases. Contaminants found in levels exceeding background levels in the area are assumed to be site-related.
Surface Deposits
The following is a discussion of hazardous substances found in surface deposits at the site. These deposits include mine tailings, mill debris, waste rock piles, and dredge spoils. (Surface deposits are described more thoroughly in the Pathways Analyses section of this document.) Surface deposit materials have been deposited throughout the site in creeks and their floodplains, and, as such, are widespread in creek sediment and floodplain soil. For this reason, floodplain soil and creek sediment samples from areas impacted by site wastes are treated as surface deposits in this public health assessment.
Sampling data for site surface deposits have been collected during three previous site investigations. The combined data from these investigations, which are discussed below, are summarized in Table 1.
In the summer of 1980, a study by the University of Idaho found elevated levels of arsenic, cobalt, copper, and iron in site sediments and tailings. The highest contaminant levels were found in stream sediments impacted by acid drainage and surface runoff from the site [6].
In October 1992, RCG/Hagler-Bailly conducted an extensive investigation of site surface deposits. A total of 28 samples were collected from surface deposits in the Big Deer Creek and Blackbird Creek drainage basins. (See Figures 3 and 4 for the surface deposit sampling locations). The sampling results revealed significantly elevated concentrations of arsenic (16,900 mg/kg max.), cobalt (7,410 mg/kg), copper (20,200 mg/kg), iron (234,000 mg/kg), nickel (410 mg/kg), and zinc (298 mg/kg) in waste rock piles, mill debris, tailings, and/or floodplain soil throughout the site. The highest contaminant levels were generally found in waste piles from the open surface pit and in mill debris recently dumped on the tailing impoundment. Chromium, lead, and manganese concentrations in the surface deposit samples were not greater than average background concentrations near the site [1].
The most recent sampling of site surface deposits was conducted by an Ecology and Environment
Inc., Technical Assistance Team (TAT) in April 1993. The TAT collected five samples of mine
tailings and mill waste from the tailings impoundment. The analysis of these samples showed
arsenic, copper, nickel, and zinc at elevated levels, similar to the levels found in the October
1992 RCG/Hagler-Bailly study. No results were reported, however, for cobalt, iron, or
manganese [9].
Table 1.
Rock, Mill
Debris, Dredge Spoils)
| CONTAMINANT | Background Concentration Range (mg/kg) (soil/sediment samples from unimpacted areas) |
SURFACE DEPOSITS CONCENTRATION RANGE (mg/kg) | Comparison Value | |
| mg/kg | Source | |||
| Arsenic | 11.1 - 148 | <50 - 16,900 | 200 | RMEG |
| Chromium | 18.2 - 105 | 13.3 - 98.4 | 4,000 | RMEG |
| Cobalt | 13.5 - 130 | 26.5 - 7,410 | none | none |
| Copper | 15 - 225 | 100 - 29,000 | none | none |
| Iron | 11,000 -42,300 | 10,422 - 234,000 | none | none |
| Lead | 4.1 - 4.9 | 0.8 - 14.4 | none | none |
| Manganese | 383 - 1,060 | 64.7 - 657 | 4,000 | RMEG |
| Nickel | 14.7 - 54.2 | 4.9 - 410 | 10,000 | RMEG |
| Zinc | 24.1 - 47.9 | ND(5.6) - 298 | 200,000 | RMEG |
Groundwater
Sampling data from several previous investigations are available for groundwater discharged from mine adits and site seeps. These data are summarized in Table 2 and discussed below [1].
In 1969, the Idaho Mining Company collected 120 samples of water from the 6850 adit and 115 samples from the 7265 adit, and found cobalt concentrations as high as 77,200 ug/L and copper concentrations over 90,000 ug/L.
From 1974-1976, Baldwin collected 57 and 16 samples from the 6850 and 7265 adits, respectively. These samples contained a maximum of 315,000 ug/L cobalt, 1,670,000 ug/L copper, and 52,200 ug/L manganese. Baldwin also collected 34 samples from site seeps and found cobalt at a maximum of 106,000 ug/L, copper at maximum of 200,000 ug/L, and manganese at a maximum of 43,000 ug/L.
In 1986, Bechtel collected a single sample from the 7265 adit and found a copper concentration of 140,000 ug/L. Bechtel (in 1984) also sampled 5 seeps and found copper concentrations up to 625,000 ug/L.
The Idaho DEQ collected 4 samples between 1979 and 1992 from the 6850 adit and found the following maximum contaminant levels: cobalt, 31,000 ug/L; copper, 58,300 ug/l; manganese, 4,490 ug/L; nickel 387 ug/L; and zinc 247 ug/L. In 1981, the DEQ collected a single sample from a waste pile seep and found cobalt at 103,800 ug/L, and copper at 210,500 ug/L.
In October 1992, RCG/Hagler collected 9 groundwater discharge samples from seeps and adits,
including the 6850 and 7265 adits. (The sampling locations are shown in Figures 5 and 6.) The
analytical results indicated that concentrations of arsenic (930 ug/L max.), cobalt (74,900 ug/L),
copper (124,000 ug/L), iron (159,000 ug/L), manganese (13,400 ug/L), nickel (1,390 ug/L), and
zinc (2,100 ug/L) in water from the adits and seeps were significantly elevated above background
surface water concentrations. Lead levels in the seep and adit discharges were slightly elevated
over background levels, while chromium levels were not elevated.
Table 2
| CONTAMINANT | Background Concentration Range (unimpacted surface water)(ug/L) |
GROUNDWATER CONCENTRATION RANGE (ug/L) | Comparison Value | |
| ug/L | Source | |||
| Arsenic | ND(1.6) - 2.1 | ND(1.6) - 930 | 10 | RMEG |
| Chromium | ND(2.9) | ND(2.9) - 5.0 | 100 | LTHA/ MCL |
| Cobalt | ND(1.0) - 6.3 | ND(1.3) - 315,000 | none | none |
| Copper | ND(1.0) - 7.5 | 8.5 - 1,670,000 | 1,000 | MCLG |
| Iron | 35.6 - 151 | 138 - 210,000 | none | none |
| Lead | ND(1.1) - 1.3 | ND(1.2) - 3.9 | 15 | ACTION LEVEL |
| Manganese | ND(0.6) - 3.0 | 3.9 - 52,200 | 200 | RMEG/ MCLG |
| Nickel | ND(10.6) | ND(10.6) - 1,390 | 700 | RMEG |
| Zinc | ND(5.7) - 7.8 | ND(5.2) - 2,100 | 2,000 | LTHA |
Surface Water
Since the late 1960s, many site investigations have documented elevated concentrations of contaminants, including arsenic, cobalt, copper, iron, manganese, nickel, and zinc, in creeks downstream of the site mining facilities. These investigations indicate that Bucktail, Big Deer, Meadow, Blackbird, and Panther Creeks have been adversely affected by the site. The data from these investigations are summarized in Table 3 [1].
The most recent investigation of area surface waters was conducted by RCG/Hagler in October
1992. A total of 28 surface water samples were collected from area creeks including Bucktail,
South Fork Big Deer, Big Deer, Meadow, Blackbird, West Fork Blackbird, and Panther Creeks.
Background surface water samples were collected at 5 locations: 1) West Fork Blackbird Creek
above the tailings dam; 2) Blackbird Creek above the water supply pond; 3) South Fork Big Deer
Creek above Bucktail Creek; 4) Big Deer Creek above South Fork Big Deer Creek; and 5)
Panther Creek above Blackbird Creek (see Figures 5 and 6 for the surface water sampling
locations). The October 1992 sampling results, which are included in Table 3, indicated that
arsenic, cobalt, copper, iron, manganese, nickel, and zinc have been released from the site to
surface waters in the Big Deer Creek and Blackbird Creek drainage basins. In fact, these
contaminants were found in Bucktail, South Fork Big Deer, Big Deer, Meadow, West Fork
Blackbird, and Blackbird Creeks at levels significantly elevated above background surface water
levels. Contaminant concentrations were somewhat elevated in Panther Creek downstream of its
confluence with Blackbird Creek relative to upstream Panther Creek levels. In general,
contaminant concentrations in area surface waters decreased with increasing distance from
contamination sources (i.e., surface deposits, adit discharges, seeps) [1].
Table 3
| CONTAMINANT | Background Concentration Range (unimpacted surface water) (ug/L) |
SURFACE WATER CONCENTRATION RANGE (ug/L) |
Comparison Value | |
| ug/L | Source | |||
| Arsenic | 1 - 2.1 | <1 - 160 | 10 | RMEG |
| Chromium | ND(2.9) | ND(2.9) - 3,710 | 100 | LTHA/ MCL |
| Cobalt | ND(1.0) - 388 | <1 - 625,000 | none | none |
| Copper | ND(1.0) - 295 | <1 - 2,220,000 | 1,000 | MCLG |
| Iron | 30 - 510 | ND(6.8) - 25,400 | none | none |
| Lead | ND(1.1) - 1.3 | ND(0.4) - 35.0 | 15 | ACTION LEVEL |
| Manganese | ND(0.6) - 3.0 | 1.2 - 258,000 | 200 | RMEG/ MCLG |
| Nickel | ND(10.6) | <9.0 - 932 | 700 | RMEG |
| Zinc | ND(5.7) - 14.1 | ND(2.7) - 2,800 | 2,000 | LTHA |
B. Quality
Assurance and Quality ControlIn preparing this public health assessment, ATSDR has relied on the information provided in the
referenced documents. We assume that adequate quality assurance and quality control measures
were following regarding chain of custody, laboratory procedures, and data reporting. The
validity of the analyses, conclusions, and recommendations in this public health assessment is
contingent upon the completeness and reliability of the referenced documents.
C. Physical
The Blackbird Mine site has features typical of inactive mines in mountainous areas, including
old mine equipment and structures, open mine adits, steep roads, sheer drops, large waste rock
piles, and a tailings impoundment dam. These features could pose physical hazards to persons
trespassing on the site property, especially children. However, due to the site's remote location
and lack of nearby residences, access by children is unlikely.
PATHWAYS
To determine whether individuals may be exposed to contaminants from a site, ATSDR evaluates the environmental and human components, or pathways, leading to human contact with contaminants. This pathway analysis considers five elements: 1) a source of contamination; 2) an environmental media (such as air, water, or soil) in which contaminants are present or are transported; 3) a point of exposure; 4) a route of exposure (such a inhalation, ingestion, or skin contact); and 5) an exposed population.
ATSDR classifies an exposure pathway as completed or potential. Completed exposure pathways require that all five pathway elements exist and indicate that exposure to a contaminant is likely in the past, present, or future. Potential exposure pathways are those for which one or more of the five pathway elements are missing, or not clearly defined, but could exist. Potential exposure pathways indicate that people may have been exposed in the past, may be occurring now, or may occur in the future. A possible exposure pathway can be eliminated when one or more of the pathway elements is missing and will never exist.
Completed and potential exposure pathways for the Blackbird Mine site are summarized in
Tables 4 and 5, respectively. The discussion that follows includes only those exposure pathways
that are believed to be important or relevant to the site.
Table 4
| PATHWAY NAME | TIME | |||||
| SOURCE | MEDIUM | POINT OF EXPOSURE | ROUTE OF EXPOSURE | EXPOSED POPULATION | ||
| Surface Deposits | Mine ore/ wastes |
Surface Deposits (e.g., tailings, waste rock) |
Mine site (esp. tailings & waste rock disposal areas) | Ingestion Skin Contact |
Site workers, Trespassers | Past Present Future |
| Surface Waters | Mine ore/ wastes, Acid mine drainage |
Surface Water & Sediments | Area creeks, Mine adits & seeps | Ingestion Skin contact |
Trespassers,
National Forest
users (e.g. hikers),
Site workers |
Past Present Future |
| Air | Mine ore/ wastes |
Ambient Air | Mine site & surrounding area | Inhalation | Site workers | Past Present Future |
Table 5
. Potential Exposure Pathways| PATHWAY NAME | TIME | |||||
| SOURCE | MEDIUM | POINT OF EXPOSURE | ROUTE OF
EXPOSURE |
EXPOSED
POPULATION |
||
| Groundwater | Mine
ore/wastes, Acid mine drainage |
Groundwater | Downstream residences | Ingestion | Forest service personnel, Downstream residents and inn guests | Past Present Future |
| Fish | Mine
ore/wastes, Acid mine drainage |
Fish | Residences, Fishing and/or Camping Sites | Ingestion | Recreational users of Panther Creek | Past Present Future |
A. Completed
Exposure PathwaysSurface Deposits
Previous mining and ore processing activities at the Blackbird Mine have resulted in contaminated surface deposits at the site. These deposits include waste rock piles, mine tailings, dredge spoils, and mill debris. Waste rock piles consist of material extracted to reach the ore and then discarded without being processed. The piles were generally deposited near the adit (or mine opening) from which the rock was obtained, often in surface water drainage areas. In addition, a large amount of waste rock from the open surface pit (Blacktail Pit), where significant surface mining was conducted, was deposited in the headwaters of Blacktail and Meadow Creeks. Waste rock at the site contains several different types of sulfide materials that can release acid and high levels of metals when deposited on the surface. Mine tailings are a by-product of the ore milling processing that was conducted at the site. More than 2 million cubic yards of tailings generated by the ore processing operations were deposited in the Blackbird Creek drainage basin. Most of the tailings were disposed of behind a large dam on the West Fork of the Blackbird Creek. However, some tailings were deposited directly into Blackbird Creek or along its banks. Dredge soils include sediments dredged from Blackbird Creek and placed along the banks of the creek. Mill debris, which was deposited in several small piles on top of the tailings impoundment, likely consists of low grade concentrate from past ore processing operations.
Surface deposits at the site contain heavy metals, including arsenic, cobalt, copper, iron, nickel and zinc. The highest contaminant levels were generally found in waste rock piles from the open surface pit and in mill debris recently dumped on the tailings impoundment. Over the years, a number of people have likely come in contact with contaminants in site surface deposits including former mine employees, previous site investigations, current on-site remediation workers, forest service personnel, and site trespassers. Exposure to these contaminants would likely have occurred through incidental ingestion, inhalation, and possible skin contact. Of those groups, former mine employees would have been at greatest risk for significant exposure since they would have spent much more time at the site and would have a much greater opportunity for close contact with site contaminants. Current site workers, who are involved in the on-going site removal activities (i.e., construction of tailings diversion channel), are also subject to exposure to contaminants, especially from mine tailings.
Surface Waters
Heavy metals, including arsenic, cobalt, copper, iron, manganese, nickel, and zinc, have been released from the site into area surface waters (i.e., creeks) by several mechanisms.
First, metals have been released directly from metal-containing materials, such as tailings and waste rock, spilled or dumped into the surface waters themselves. Second, metals have been released into area creeks indirectly from site surface deposits (e.g, waste rock and tailings piles). Specifically, surface runoff (i.e., stormwater, snowmelt) and groundwater discharged from seeps, flowing over and through the surface deposits, causes physical erosion and leaching of soluble metals within the deposits. In addition, acid produced by the oxidation and dissolution of iron sulfide minerals leaches metals from other sulfide minerals within the surface deposits. Third, groundwater contaminated by contact with site surface deposits or by acid mine water can discharge metals into area surface waters directly or via seeps or mine adits.
As discussed above, acid mine water (usually referred to as acid mine drainage) is formed when iron sulfide minerals are oxidized and dissolved as a result of contact with oxygen and water. The acid mine drainage, which is characterized by a low pH and high sulfate content, is primarily generated in underground mine workings. However, acid mine drainage can also be formed in surface deposits, such as tailings and waste rock piles, that contain iron sulfides. The acid produced can dissolve other sulfides which do not produce acid themselves, thereby releasing sulfate and heavy metals. At the Blackbird Mine site, acid mine drainage discharged from underground mine workings (via seeps and adits) and from surface deposits has contaminated surface waters of area creeks with arsenic, cobalt, copper, iron, manganese, nickel, and zinc.
The oxidation of primary sulfides by the acid in acid mine drainage can also result in the formation of alteration minerals, primarily on the surface of tailings deposits and waste rock piles. The alteration minerals are generally very soluble in water, especially water that is acidic. Leachate tests conducted on site surface deposit samples that contained alteration minerals generally showed high levels of metals, including cobalt, copper, iron, manganese, nickel, and zinc. Therefore, it is likely that these metals are leached to site groundwaters and surface waters as alteration minerals are dissolved by rainfall runoff, snowmelt, or shallow groundwater.
In addition to causing high metal levels in the surface waters of area creeks, acid mine drainage from the site has also resulted in metal contamination of creek sediments. Specifically, as surface waters contaminated by acid mine drainage mix with cleaner downstream creeks, the pH of the water increases, and dissolved metals (especially iron) precipitate from solution as metal oxides and hydroxides. The metals can also be removed from solution by either co-precipitation with or adsorption onto iron hydroxides, which produce orange-brown stains on rocks and in streambeds. (Note: During the November 1993, ATSDR site visit, extensive orange-brown staining was observed along the Blackbird Creek streambed.) The resulting transfer of metals from the water column to the stream bottom can cause significant metal contamination of the creek sediments. At the Blackbird site, high levels of metals, including cobalt, copper, and iron, have been found in creek sediments by previous sampling investigations.
In the past, a number of people have likely been exposed to metals in area surface waters impacted by the site including former mine employees, previous site investigations, current on-site remediation workers, forest service personnel, site trespassers, and users of the national forest (e.g., hikers, fisherman). Exposure to these contaminants would likely have occurred through drinking of water from the creeks (ingestion) and through skin contact. For example, former mine employees or site workers may have occasionally used water from one of the site creeks for drinking water purposes while working at the site. This was probably an uncommon occurrence since potable water for the mine office, shop, mill, and other associated buildings was supplied by a small reservoir which impounded water on upper Blackbird Creek. This reservoir was upgradient from the mine and was not impacted by site contamination. Trespassers and area hikers, however, would be more likely to drink water from the creeks since they would probably be less aware of creek contamination and would likely have no other source of drinking water. A few years ago, it was reported that two hikers drank water from one of the area creeks (possibly Bucktail Creek), became ill, and were hospitalized for metal poisoning. (ATSDR has been unable to confirm this report.) Since then, the U.S. Forest Service has posted signs along Blackbird Creek below the site indicating that the creek is not safe for drinking. These signs have probably reduced the likelihood of further human exposures to contaminants in the creek. However, it is unknown whether other contaminated creeks in the site area, especially those in the higher, more remote areas of the site, are similarly posted. Hikers and fisherman would also be likely to wade in or walk through area creeks, especially during the warmer, summer months when fishing and recreation activities most often occur. As such, these persons could be exposed to metals in the creek waters and bottom sediments through contact with their legs, ankles, and feet.
Ambient Air
Ambient air at the Blackbird Mine site is subject to contamination by site activities which
generate airborne solids and fugitive dust. In the past, these activities have included blasting of
rock during exploration or mining operation; drilling of wells or boreholes; earthmoving
operations; road construction; and vehicular traffic on mine roads. Currently, site activities
involving the construction of the surface diversion channel across the tailings impoundment and
associated spillway are potential sources of airborne emissions. In particular, the excavation and
regrading of tailings on top of the tailings pile, the drilling of and installation of rock bolts for the
channel spillway, and the movement of trucks and construction equipment, are likely to generate
substantial amounts of airborne solids (e.g., tailings, soil) and fugitive dust. Site workers
involved in those activities have likely inhaled some of the airborne particles, and, as a result,
have likely been exposed to metals contained in or on the particles. In September 1993, for
example, representatives of the U.S. Bureau of Reclamation and the EPA oversight contractor
observed a drilling crew working without respiratory protection during the installation of rock
bolts for the spillway apron. Because of the large amounts of dust being generated by the drilling
operations, the representatives suggested that either respirators be worn by the drilling crew or
water be used for dust suppression [10,11].
B. Potential
Groundwater
As discussed above, groundwater at the Blackbird Mine site has been contaminated by contact with underground mine workings and surface deposits (e.g, tailings, waste rock). Specifically, acid mine drainage formed by the oxidation of iron sulfides in underground mine workings and in surface deposits has leached metals, including arsenic, cobalt, copper, manganese, nickel, and zinc, into site groundwaters. In addition, the infiltration of stormwater through the bottom of the Blacktail Pit, a large source of mining-induced recharge, is believed to be a significant contributor to groundwater contamination at the site. Contaminated groundwater is discharged to area creeks directly as underflow and indirectly from seeps and mine adits.
According to a USFS groundwater hydrology report, no significant groundwater resources have been developed in the site area. In addition, the report indicates that regional transport of groundwater beyond the immediate site drainage basins is negligible.
ATSDR is not aware of any use of groundwater for water supply purposes in the site area, except as discussed below. The Cobalt Ranger Station, which is located about 6 miles from the site, reportedly uses a spring as potable water source. However, this spring is located upgradient of the Blackbird site and, therefore, is unlikely to affected by site contamination. The Panther Creek Inn, which is located at the confluence of Blackbird Creek and Panther Creek, is reported to obtain its water from a "sand spike" (likely a shallow well point) in the creek floodplain. This water source has been sampled in the past; however, ATSDR was unable to obtain the sampling results. Therefore, at the present time, it cannot be confirmed that the inn's drinking water has not been impacted by contaminants from the site.
Other persons living in the site area include the remaining residents of the town of Cobalt (estimated population 13) and a few permanent or seasonal residents along Panther Creek downstream of Cobalt. The source of drinking water for these persons is unknown, but is not likely be significantly impacted by site contamination due to the significant distance and the presence of hydrologic barriers between the site and the residences.
Fish
Acid and heavy metals, especially copper, in drainage from the Blackbird Mine site have adversely impacted creeks in the Blackbird and Big Deer Creek drainage basins to the point that point that fish are essentially non-existent in these creeks. Blackbird Creek and Big Deer Creek, in turn, have discharged contaminants into Panther Creek, resulting in a severe reduction in the number of fish that inhabit the lower portion of the creek [5].
Since fish are reportedly absent from Blackbird, Meadow, Bucktail, and Big Deer Creeks, the
potential for human exposure to metals as a result of consuming fish from these creeks is
minimal. However, 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. Exposure to
metals in Panther Creek is possible since fish can bioaccumulate metals, especially cobalt,
copper, manganese, and zinc, either directly from ingesting metal contaminated creek water and
sediment or indirectly by consuming other fish that have accumulated metals. This is especially
true for predatory fish, such as trout, and bottom dwelling fish, which tend to accumulate higher
levels of metals. However, since no fish tissue sampling data are available, the actual levels of
metals in Panther Creek fish are unknown. As a result, ATSDR cannot evaluate the significance
of this potential exposure pathway.
PUBLIC
A. Toxicological Evaluation
Introduction
In this section, we will discuss the health effects of current and potential exposure to contaminants of health concern at Blackbird Mine Tailings. In the toxicological implications section, we will only discuss pathways of exposure that are considered to be completed in the past, present, and future. Individuals that have worked at the site in different capacities (miners, forest service rangers, remediation workers) and occasional trespassers (hikers or hunters) may have been exposed to contaminants in surface deposits, surface water, and air. These individuals could have been exposed to these contaminants by incidental ingestion, dermal contact, or inhalation of the site contaminants.
We are unable to evaluate exposure occurring from inhalation of site contaminants since no ambient air data is available for review. Records were unavailable to review the past occupational practices at the mine. Certain metals that have been found in the surface deposits including cobalt, copper, arsenic, iron, manganese can be absorbed and enter the blood stream after they are inhaled. The amount of absorption via inhalation is dependent on the particulate size of the metal absorbed.
Operations such as rock blasting and drilling may have produced dust that workers could have inhaled. Site files indicate that in September 1993, representatives of the U.S. Bureau of Reclamation and an EPA oversight contractor observed a drilling crew with no respiratory protection during the installation of rock bolts for a spillway apron. Because a substantial amount of dust was generated by the drilling operation, representatives suggested that respirators be worn by the drilling crews or that water be utilized for dust suppression. No ambient air data was available to evaluate the potential for exposure of this event. Site files indicate that air monitoring had been conducted at the onset of site activities. The monitoring results did not indicate that exposure to particulate matter had exceeded occupational safety guidelines. No speciated data on the composition of the particulate was available for review.
Dermal exposure to metals in surface water could have occurred or may occur from wading or hand washing in the surface water of the creek. Dermal absorption of site contaminants from the surface water does not represent a significant pathway of exposure. No adverse health effects are expected to occur from these activities since there is minimal absorption of the metals through the skin from the short duration of these activities.
Dermal contact with mine waste may have occurred in the past, present, or future during mining operations which produced dust or particulate matter. Metals in surface deposits which exceed environmental comparison values include arsenic, cobalt, copper, iron, and manganese. Small amounts of arsenic can be absorbed through the skin. Occupational studies of exposure to inorganic arsenic indicate that a dermatitis can be produced after prolonged exposure. Exposure to copper dust has been reported to produce eye irritation in factory workers. Some individuals may be allergic to copper. An allergic contact dermatitis can be produced by contact with the metal. No studies could be located on the health effects in humans after dermal contact with cobalt, iron, or manganese.
Although there are contaminants that exceed health comparison values in the groundwater, we will not discuss this pathway since there are no individuals consuming potable water supplies from this source. The local tavern draws it's potable water supply from a sand spike. The forest ranger station obtains it's potable water supply from an underground spring (Dummy Creek, upgradient of the mine). The on-site potable water supply was supplied by a small reservoir which impounded water on upper Blackbird Creek. This reservoir is upgradient of the mine, and, according to site file documents, is not contaminated.
The most likely scenario of exposure is a trespasser such as a hiker or hunter consuming surface water from one of the contaminated creeks. Metals including arsenic, chromium, cobalt, copper, iron, lead, manganese, nickel, and zinc have been detected in the surface water of the creeks around the mine including Bucktail, South Fork Big Deer, Big Deer Meadow, West Fork Blackbird, and Blackbird. Blackbird Creek is the most accessible creek to a trespasser entering the site. This creek is clearly posted at the entry to the mine. The other creeks are more remote and located in more mountainous terrain. We will evaluate the potential health effects of an adult (such as a hiker or hunter) consuming two liters of water from the maximum concentrations of metals found in the impacted creeks on a short term basis (less than 14 days per year) for the metals detected above environmental comparison values in the surface water.
Arsenic
Most individuals consuming the surface water from the contaminated creeks would not experience adverse health effects from the arsenic contamination in the surface water. However, there are some individuals that may be sensitive to the effects of arsenic. Ingestion of low levels of arsenic (20-60 ug/kg/day) can produce characteristic symptoms of arsenic toxicity such as gastrointestinal irritation, anemia, neuropathy, skin lesions, vascular lesions, and hepatic injury. The more severe of these effects are produced with the increasing duration of exposure [12].
Chromium
There are no adverse health effects expected to occur from ingestion of the surface water in the contaminated creeks at the reported concentration of chromium for a short term exposure [13].
Cobalt
There were no studies in humans indicating health effects from cobalt from an occasional ingestion exposure (less than 14 days per year). Data was reviewed from human studies where exposure to different levels of cobalt occurred for greater that 14 days but less one year. Based on these studies, an individual might experience gastrointestinal upset from consuming the water from the contaminated creeks. These gastrointestinal effects may include nausea, vomiting, and diarrhea [14].
Copper
An individual consuming water from the creek may experience signs of gastrointestinal upset such as diarrhea, nausea, vomiting, and abdominal pain and a metallic taste in their mouth at the concentration of copper detected in the contaminated creeks [15].
Iron
Elevated concentrations of iron are commonly found in water supplies. Most elevated concentrations of iron are considered to be a nuisance because of the bad taste and staining. An individual might experience slight gastrointestinal upset (vomiting) from consuming water from the contaminated creeks at the iron concentrations reported [16].
Lead
There are no expected health effects to occur in adults ingesting surface water from the creek at the reported concentration of lead [17].
Manganese
There are no adverse health effects expected to occur from ingestion of the surface water in the creeks at the reported concentration of manganese for a short term exposure [18].
Nickel
Gastrointestinal upset such as nausea, vomiting, and diarrhea might be experienced by an individual consuming water from the creeks as a result of exposure to elevated levels of nickel in the surface water [19].
Zinc
Several studies have indicated that symptoms of gastrointestinal distress have been reported after
individuals consumed solutions containing zinc at the exposure dose that individuals might
encounter if they consumed two liters from the contaminated creeks. These gastrointestinal
effects included vomiting, diarrhea, and abdominal cramps [20].
B. Health
There were no relevant health outcome data to review for this site.
C. Community
ATSDR was unable to identify any community health concerns related to the site.
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