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PUBLIC HEALTH ASSESSMENT

BLACKBIRD MINE
COBALT, LEMHI COUNTY, IDAHO


ENVIRONMENTAL CONTAMINATION AND OTHER HAZARDS

This section of the public health assessment describes previous environmental samplingconducted at the Blackbird Mine site and identifies contaminants of concern found in specificsite media.

ATSDR selects contaminants of concern based upon the following:

  1. concentrations of contaminants on and off the site;

  2. sampling locations and frequency, field data quality, and laboratory data quality;

  3. comparison of on-site and off-site concentrations with health assessment comparison valuesfor noncarcinogenic and carcinogenic endpoints; and

  4. community health concerns.

It is emphasized that identification of a contaminant of concern in this section does not mean thatexposure to it will cause adverse health effects. Instead, the selected contaminants are those thatwill 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 thatare used to select environmental contaminants for further evaluation. These values includeEnvironmental Media Evaluation Guides (EMEGs), Reference dose-based Media EvaluationGuides (RMEGs), Cancer Risk Evaluation Guides (CREGs), and other relevant guidelines.

    EMEGs are media-specific screening values derived by ATSDR from ATSDR minimal risklevels (MRLs), while RMEGs are derived from EPA reference doses (RfDs). ATSDR MRLsand EPA RfDs are estimates of daily exposure to a contaminant that are unlikely to causeadverse, 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 millionpersons exposed to that contaminant over a lifetime.

    Lifetime Health Advisories (LTHAs), which are derived by EPA, represent the level of acontaminant in drinking water (with a margin of safety) at which adverse, non-carcinogenichealth effects would not be anticipated during a lifetime (70 years) exposure.

    Maximum Contaminant Levels (MCLs) represent contaminant concentrations that EPA deemsprotective of public health (considering the availability and economics of water treatmenttechnology) 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 atlevels at which no known or anticipated adverse human health effect occurs and which allows anadequate margin of safety. When there is no safe level for a contaminant, the MCLG is set atzero. While MCLs are enforceable, regulatory concentrations, MCLGs are not.

    A. Environmental Contamination

    Numerous investigations regarding the sources, fate, and impacts of hazardous substancesreleased from the Blackbird Mine site have been conducted since the late 1960s. Majorinvestigations include those by the U.S. Forest Service; the University of Idaho; EnvironmentalResearch and Technology; Noranda Mining Inc.; the U.S. Department of Energy; the IdahoDivision of Environmental Quality; and RCG/Hagler, Bailly, Inc.; and Ecology and EnvironmentInc. The results of these studies are discussed below.

    Note: ATSDR has not attempted to differentiate between "on-site" and "off-site" contaminationin this public health assessment because 1) exact site boundaries could not be determined fromavailable information; 2) wastes from past site operations have been deposited outside the areaswhere mining and ore processing activities occurred (e.g., tailings impounded on West ForkBlackbird Creek); 3) contaminants from the site have impacted surface waters far downstream ofthe actual site (such as Panther Creek), and 4) the exact location where samples were collectedcould not be determined in some cases. Contaminants found in levels exceeding backgroundlevels 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. (Surfacedeposits 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, floodplainsoil and creek sediment samples from areas impacted by site wastes are treated as surfacedeposits in this public health assessment.

    Sampling data for site surface deposits have been collected during three previous siteinvestigations. The combined data from these investigations, which are discussed below, aresummarized 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 werefound 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 surfacedeposits. A total of 28 samples were collected from surface deposits in the Big Deer Creek andBlackbird Creek drainage basins. (See Figures 3 and 4 for the surface deposit samplinglocations). The sampling results revealed significantly elevated concentrations of arsenic (16,900mg/kg max.), cobalt (7,410 mg/kg), copper (20,200 mg/kg), iron (234,000 mg/kg), nickel (410mg/kg), and zinc (298 mg/kg) in waste rock piles, mill debris, tailings, and/or floodplain soilthroughout the site. The highest contaminant levels were generally found in waste piles from theopen 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 averagebackground concentrations near the site [1].

    The most recent sampling of site surface deposits was conducted by an Ecology and EnvironmentInc., Technical Assistance Team (TAT) in April 1993. The TAT collected five samples of minetailings and mill waste from the tailings impoundment. The analysis of these samples showedarsenic, copper, nickel, and zinc at elevated levels, similar to the levels found in the October1992 RCG/Hagler-Bailly study. No results were reported, however, for cobalt, iron, ormanganese [9].

    Table 1.

    Contaminant Concentrations in Surface Deposits (e.g., Tailings, Waste
    Rock, Mill Debris, Dredge Spoils)
    CONTAMINANTBackground
    Concentration
    Range (mg/kg)
    (soil/sedimentsamples fromunimpacted areas)
    SURFACEDEPOSITSCONCENTRATION RANGE (mg/kg)Comparison Value
    mg/kgSource
    Arsenic11.1 - 148<50 - 16,900200RMEG
    Chromium18.2 - 10513.3 - 98.44,000RMEG
    Cobalt13.5 - 13026.5 - 7,410nonenone
    Copper15 - 225100 - 29,000nonenone
    Iron11,000 -42,30010,422 - 234,000nonenone
    Lead4.1 - 4.90.8 - 14.4nonenone
    Manganese383 - 1,06064.7 - 6574,000RMEG
    Nickel14.7 - 54.24.9 - 41010,000RMEG
    Zinc24.1 - 47.9ND(5.6) - 298200,000RMEG

    Groundwater

    Sampling data from several previous investigations are available for groundwater dischargedfrom 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 115samples from the 7265 adit, and found cobalt concentrations as high as 77,200 ug/L and copperconcentrations 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/Lcopper, and 52,200 ug/L manganese. Baldwin also collected 34 samples from site seeps andfound cobalt at a maximum of 106,000 ug/L, copper at maximum of 200,000 ug/L, andmanganese at a maximum of 43,000 ug/L.

    In 1986, Bechtel collected a single sample from the 7265 adit and found a copper concentrationof 140,000 ug/L. Bechtel (in 1984) also sampled 5 seeps and found copper concentrations up to625,000 ug/L.

    The Idaho DEQ collected 4 samples between 1979 and 1992 from the 6850 adit and found thefollowing 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 froma 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.) Theanalytical 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), andzinc (2,100 ug/L) in water from the adits and seeps were significantly elevated above backgroundsurface water concentrations. Lead levels in the seep and adit discharges were slightly elevatedover background levels, while chromium levels were not elevated.

    Table 2.

    Contaminant Concentrations in Groundwater Samples (Seep & Adit Discharges)
    CONTAMINANTBackground
    Concentration
    Range(unimpactedsurfacewater)(ug/L)
    GROUNDWATERCONCENTRATION RANGE (ug/L)Comparison Value
    ug/LSource
    ArsenicND(1.6) - 2.1ND(1.6) - 93010RMEG
    ChromiumND(2.9)ND(2.9) - 5.0100 LTHA/
    MCL
    CobaltND(1.0) - 6.3ND(1.3) - 315,000none none
    CopperND(1.0) - 7.58.5 - 1,670,0001,000MCLG
    Iron35.6 - 151138 - 210,000nonenone
    LeadND(1.1) - 1.3ND(1.2) - 3.915ACTIONLEVEL
    ManganeseND(0.6) - 3.03.9 - 52,200200RMEG/
    MCLG
    NickelND(10.6) ND(10.6) - 1,390700RMEG
    ZincND(5.7) - 7.8ND(5.2) - 2,1002,000LTHA

    Surface Water

    Since the late 1960s, many site investigations have documented elevated concentrations ofcontaminants, including arsenic, cobalt, copper, iron, manganese, nickel, and zinc, in creeksdownstream 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 fromthese investigations are summarized in Table 3 [1].

    The most recent investigation of area surface waters was conducted by RCG/Hagler in October1992. 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 Creekabove the tailings dam; 2) Blackbird Creek above the water supply pond; 3) South Fork Big DeerCreek 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 samplinglocations). The October 1992 sampling results, which are included in Table 3, indicated thatarsenic, cobalt, copper, iron, manganese, nickel, and zinc have been released from the site tosurface waters in the Big Deer Creek and Blackbird Creek drainage basins. In fact, thesecontaminants were found in Bucktail, South Fork Big Deer, Big Deer, Meadow, West ForkBlackbird, and Blackbird Creeks at levels significantly elevated above background surface waterlevels. Contaminant concentrations were somewhat elevated in Panther Creek downstream of itsconfluence 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 Concentrations in Surface Water Samples
    CONTAMINANTBackground
    Concentration
    Range(unimpactedsurface water)
    (ug/L)
    SURFACE WATER
    CONCENTRATION RANGE (ug/L)
    Comparison Value
    ug/LSource
    Arsenic1 - 2.1<1 - 16010RMEG
    ChromiumND(2.9)ND(2.9) - 3,710100 LTHA/
    MCL
    CobaltND(1.0) - 388<1 - 625,000nonenone
    CopperND(1.0) - 295<1 - 2,220,0001,000MCLG
    Iron30 - 510ND(6.8) - 25,400nonenone
    LeadND(1.1) - 1.3ND(0.4) - 35.015ACTION
    LEVEL
    ManganeseND(0.6) - 3.01.2 - 258,000200RMEG/
    MCLG
    NickelND(10.6) <9.0 - 932700RMEG
    ZincND(5.7) - 14.1ND(2.7) - 2,8002,000LTHA

    B. Quality Assurance and Quality Control

    In preparing this public health assessment, ATSDR has relied on the information provided in thereferenced documents. We assume that adequate quality assurance and quality control measureswere following regarding chain of custody, laboratory procedures, and data reporting. Thevalidity of the analyses, conclusions, and recommendations in this public health assessment iscontingent upon the completeness and reliability of the referenced documents.

    C. Physical and Other Hazards

    The Blackbird Mine site has features typical of inactive mines in mountainous areas, includingold mine equipment and structures, open mine adits, steep roads, sheer drops, large waste rockpiles, and a tailings impoundment dam. These features could pose physical hazards to personstrespassing on the site property, especially children. However, due to the site's remote locationand lack of nearby residences, access by children is unlikely.

    PATHWAYS ANALYSES

    To determine whether individuals may be exposed to contaminants from a site, ATSDRevaluates the environmental and human components, or pathways, leading to human contact withcontaminants. 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 aretransported; 3) a point of exposure; 4) a route of exposure (such a inhalation, ingestion, or skincontact); and 5) an exposed population.

    ATSDR classifies an exposure pathway as completed or potential. Completed exposurepathways require that all five pathway elements exist and indicate that exposure to a contaminantis likely in the past, present, or future. Potential exposure pathways are those for which one ormore of the five pathway elements are missing, or not clearly defined, but could exist. Potentialexposure pathways indicate that people may have been exposed in the past, may be occurringnow, or may occur in the future. A possible exposure pathway can be eliminated when one ormore of the pathway elements is missing and will never exist.

    Completed and potential exposure pathways for the Blackbird Mine site are summarized inTables 4 and 5, respectively. The discussion that follows includes only those exposure pathwaysthat are believed to be important or relevant to the site.

    Table 1.

    Completed Exposure Pathways
    PATHWAY NAMEEXPOSURE PATHWAY ELEMENTS TIME
    SOURCEMEDIUMPOINT OF EXPOSUREROUTE OF EXPOSUREEXPOSED POPULATION
    Surface Deposits Mine ore/
    wastes
    Surface Deposits
    (e.g., tailings,waste rock)
    Mine site (esp.tailings & wasterock disposalareas)Ingestion
    Skin Contact
    Site workers,TrespassersPast
    Present
    Future
    Surface WatersMine ore/
    wastes,
    Acid minedrainage
    Surface Water &SedimentsArea creeks, Mine adits &seepsIngestion
    Skin contact
    Trespassers,National Forestusers (e.g. hikers),

    Site workers

    Past
    Present
    Future
    AirMine ore/
    wastes
    Ambient AirMine site &surrounding areaInhalationSite workersPast
    Present
    Future

    Table 5.

    Potential Exposure Pathways
    PATHWAYNAME EXPOSURE PATHWAY ELEMENTS TIME
    SOURCEMEDIUMPOINT OF EXPOSUREROUTE OF EXPOSUREEXPOSED POPULATION
    GroundwaterMineore/wastes,
    Acid minedrainage
    GroundwaterDownstream residencesIngestionForest servicepersonnel,Downstream residents and innguestsPast
    Present
    Future
    FishMineore/wastes,
    Acid minedrainage
    FishResidences,Fishing and/orCamping SitesIngestionRecreationalusers of PantherCreekPast
    Present
    Future

    A. Completed Exposure Pathways

    Surface Deposits

    Previous mining and ore processing activities at the Blackbird Mine have resulted incontaminated 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 andthen discarded without being processed. The piles were generally deposited near the adit (ormine opening) from which the rock was obtained, often in surface water drainage areas. Inaddition, a large amount of waste rock from the open surface pit (Blacktail Pit), where significantsurface mining was conducted, was deposited in the headwaters of Blacktail and MeadowCreeks. Waste rock at the site contains several different types of sulfide materials that canrelease acid and high levels of metals when deposited on the surface. Mine tailings are aby-product of the ore milling processing that was conducted at the site. More than 2 millioncubic yards of tailings generated by the ore processing operations were deposited in the BlackbirdCreek drainage basin. Most of the tailings were disposed of behind a large dam on the West Forkof the Blackbird Creek. However, some tailings were deposited directly into Blackbird Creek oralong its banks. Dredge soils include sediments dredged from Blackbird Creek and placed alongthe banks of the creek. Mill debris, which was deposited in several small piles on top of thetailings impoundment, likely consists of low grade concentrate from past ore processingoperations.

    Surface deposits at the site contain heavy metals, including arsenic, cobalt, copper, iron, nickeland zinc. The highest contaminant levels were generally found in waste rock piles from the opensurface pit and in mill debris recently dumped on the tailings impoundment. Over the years, anumber of people have likely come in contact with contaminants in site surface depositsincluding former mine employees, previous site investigations, current on-site remediationworkers, forest service personnel, and site trespassers. Exposure to these contaminants wouldlikely have occurred through incidental ingestion, inhalation, and possible skin contact. Of thosegroups, former mine employees would have been at greatest risk for significant exposure sincethey would have spent much more time at the site and would have a much greater opportunity forclose contact with site contaminants. Current site workers, who are involved in the on-going siteremoval activities (i.e., construction of tailings diversion channel), are also subject to exposure tocontaminants, especially from mine tailings.

    Surface Waters

    Heavy metals, including arsenic, cobalt, copper, iron, manganese, nickel, and zinc, have beenreleased 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 andwaste rock, spilled or dumped into the surface waters themselves. Second, metals have beenreleased 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 solublemetals within the deposits. In addition, acid produced by the oxidation and dissolution of ironsulfide 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 candischarge 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 wheniron 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 primarilygenerated in underground mine workings. However, acid mine drainage can also be formed insurface deposits, such as tailings and waste rock piles, that contain iron sulfides. The acidproduced can dissolve other sulfides which do not produce acid themselves, thereby releasingsulfate and heavy metals. At the Blackbird Mine site, acid mine drainage discharged fromunderground mine workings (via seeps and adits) and from surface deposits has contaminatedsurface 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 theformation of alteration minerals, primarily on the surface of tailings deposits and waste rockpiles. 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 mineralsgenerally showed high levels of metals, including cobalt, copper, iron, manganese, nickel, andzinc. Therefore, it is likely that these metals are leached to site groundwaters and surface watersas 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 drainagefrom the site has also resulted in metal contamination of creek sediments. Specifically, assurface waters contaminated by acid mine drainage mix with cleaner downstream creeks, the pHof the water increases, and dissolved metals (especially iron) precipitate from solution as metaloxides and hydroxides. The metals can also be removed from solution by either co-precipitationwith or adsorption onto iron hydroxides, which produce orange-brown stains on rocks and instreambeds. (Note: During the November 1993, ATSDR site visit, extensive orange-brownstaining was observed along the Blackbird Creek streambed.) The resulting transfer of metalsfrom the water column to the stream bottom can cause significant metal contamination of thecreek 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 watersimpacted by the site including former mine employees, previous site investigations, currenton-site remediation workers, forest service personnel, site trespassers, and users of the nationalforest (e.g., hikers, fisherman). Exposure to these contaminants would likely have occurredthrough 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 sitecreeks for drinking water purposes while working at the site. This was probably an uncommonoccurrence since potable water for the mine office, shop, mill, and other associated buildings wassupplied by a small reservoir which impounded water on upper Blackbird Creek. This reservoirwas upgradient from the mine and was not impacted by site contamination. Trespassers and areahikers, however, would be more likely to drink water from the creeks since they would probablybe less aware of creek contamination and would likely have no other source of drinking water. Afew years ago, it was reported that two hikers drank water from one of the area creeks (possiblyBucktail Creek), became ill, and were hospitalized for metal poisoning. (ATSDR has been unableto confirm this report.) Since then, the U.S. Forest Service has posted signs along BlackbirdCreek below the site indicating that the creek is not safe for drinking. These signs have probablyreduced the likelihood of further human exposures to contaminants in the creek. However, it isunknown whether other contaminated creeks in the site area, especially those in the higher, moreremote areas of the site, are similarly posted. Hikers and fisherman would also be likely to wadein or walk through area creeks, especially during the warmer, summer months when fishing andrecreation activities most often occur. As such, these persons could be exposed to metals in thecreek 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 whichgenerate airborne solids and fugitive dust. In the past, these activities have included blasting ofrock during exploration or mining operation; drilling of wells or boreholes; earthmovingoperations; road construction; and vehicular traffic on mine roads. Currently, site activitiesinvolving the construction of the surface diversion channel across the tailings impoundment andassociated spillway are potential sources of airborne emissions. In particular, the excavation andregrading of tailings on top of the tailings pile, the drilling of and installation of rock bolts for thechannel spillway, and the movement of trucks and construction equipment, are likely to generatesubstantial amounts of airborne solids (e.g., tailings, soil) and fugitive dust. Site workersinvolved 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, forexample, representatives of the U.S. Bureau of Reclamation and the EPA oversight contractorobserved a drilling crew working without respiratory protection during the installation of rockbolts for the spillway apron. Because of the large amounts of dust being generated by the drillingoperations, the representatives suggested that either respirators be worn by the drilling crew orwater be used for dust suppression [10,11].

    B. Potential Exposure Pathways

    Groundwater

    As discussed above, groundwater at the Blackbird Mine site has been contaminated by contactwith 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 andin surface deposits has leached metals, including arsenic, cobalt, copper, manganese, nickel, andzinc, into site groundwaters. In addition, the infiltration of stormwater through the bottom of theBlacktail Pit, a large source of mining-induced recharge, is believed to be a significantcontributor to groundwater contamination at the site. Contaminated groundwater is discharged toarea creeks directly as underflow and indirectly from seeps and mine adits.

    According to a USFS groundwater hydrology report, no significant groundwater resources havebeen developed in the site area. In addition, the report indicates that regional transport ofgroundwater 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, exceptas 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 ofthe Blackbird site and, therefore, is unlikely to affected by site contamination. The PantherCreek Inn, which is located at the confluence of Blackbird Creek and Panther Creek, is reportedto obtain its water from a "sand spike" (likely a shallow well point) in the creek floodplain. Thiswater source has been sampled in the past; however, ATSDR was unable to obtain the samplingresults. Therefore, at the present time, it cannot be confirmed that the inn's drinking water hasnot 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 Creekdownstream of Cobalt. The source of drinking water for these persons is unknown, but is notlikely be significantly impacted by site contamination due to the significant distance and thepresence of hydrologic barriers between the site and the residences.

    Fish

    Acid and heavy metals, especially copper, in drainage from the Blackbird Mine site haveadversely impacted creeks in the Blackbird and Big Deer Creek drainage basins to the point thatpoint 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 thenumber of fish that inhabit the lower portion of the creek [5].

    Since fish are reportedly absent from Blackbird, Meadow, Bucktail, and Big Deer Creeks, thepotential for human exposure to metals as a result of consuming fish from these creeks isminimal. However, persons who fish Panther Creek below Blackbird Creek or Big Deer Creekcould potentially be exposed to heavy metals by eating fish caught in the creek. Exposure tometals in Panther Creek is possible since fish can bioaccumulate metals, especially cobalt,copper, manganese, and zinc, either directly from ingesting metal contaminated creek water andsediment or indirectly by consuming other fish that have accumulated metals. This is especiallytrue for predatory fish, such as trout, and bottom dwelling fish, which tend to accumulate higherlevels of metals. However, since no fish tissue sampling data are available, the actual levels ofmetals in Panther Creek fish are unknown. As a result, ATSDR cannot evaluate the significanceof this potential exposure pathway.

    PUBLIC HEALTH IMPLICATIONS

    A. Toxicological Evaluation

    Introduction

    In this section, we will discuss the health effects of current and potential exposure tocontaminants of health concern at Blackbird Mine Tailings. In the toxicological implicationssection, we will only discuss pathways of exposure that are considered to be completed in thepast, 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) mayhave been exposed to contaminants in surface deposits, surface water, and air. These individualscould have been exposed to these contaminants by incidental ingestion, dermal contact, orinhalation of the site contaminants.

    We are unable to evaluate exposure occurring from inhalation of site contaminants since noambient air data is available for review. Records were unavailable to review the pastoccupational practices at the mine. Certain metals that have been found in the surface depositsincluding cobalt, copper, arsenic, iron, manganese can be absorbed and enter the blood streamafter they are inhaled. The amount of absorption via inhalation is dependent on the particulatesize of the metal absorbed.

    Operations such as rock blasting and drilling may have produced dust that workers could haveinhaled. Site files indicate that in September 1993, representatives of the U.S. Bureau ofReclamation and an EPA oversight contractor observed a drilling crew with no respiratoryprotection during the installation of rock bolts for a spillway apron. Because a substantialamount of dust was generated by the drilling operation, representatives suggested that respiratorsbe worn by the drilling crews or that water be utilized for dust suppression. No ambient air datawas available to evaluate the potential for exposure of this event. Site files indicate that airmonitoring had been conducted at the onset of site activities. The monitoring results did notindicate that exposure to particulate matter had exceeded occupational safety guidelines. Nospeciated 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 orhand washing in the surface water of the creek. Dermal absorption of site contaminants from thesurface water does not represent a significant pathway of exposure. No adverse health effects areexpected to occur from these activities since there is minimal absorption of the metals throughthe skin from the short duration of these activities.

    Dermal contact with mine waste may have occurred in the past, present, or future during miningoperations which produced dust or particulate matter. Metals in surface deposits which exceedenvironmental comparison values include arsenic, cobalt, copper, iron, and manganese. Smallamounts of arsenic can be absorbed through the skin. Occupational studies of exposure toinorganic arsenic indicate that a dermatitis can be produced after prolonged exposure. Exposureto copper dust has been reported to produce eye irritation in factory workers. Some individualsmay be allergic to copper. An allergic contact dermatitis can be produced by contact with themetal. No studies could be located on the health effects in humans after dermal contact withcobalt, iron, or manganese.

    Although there are contaminants that exceed health comparison values in the groundwater, wewill not discuss this pathway since there are no individuals consuming potable water suppliesfrom this source. The local tavern draws it's potable water supply from a sand spike. The forestranger 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 reservoirwhich 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 surfacewater 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 creeksaround the mine including Bucktail, South Fork Big Deer, Big Deer Meadow, West ForkBlackbird, and Blackbird. Blackbird Creek is the most accessible creek to a trespasser enteringthe site. This creek is clearly posted at the entry to the mine. The other creeks are more remoteand located in more mountainous terrain. We will evaluate the potential health effects of anadult (such as a hiker or hunter) consuming two liters of water from the maximum concentrationsof metals found in the impacted creeks on a short term basis (less than 14 days per year) for themetals detected above environmental comparison values in the surface water.

    Arsenic

    Most individuals consuming the surface water from the contaminated creeks would notexperience 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 levelsof arsenic (20-60 ug/kg/day) can produce characteristic symptoms of arsenic toxicity such asgastrointestinal 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 thecontaminated 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 occasionalingestion exposure (less than 14 days per year). Data was reviewed from human studies whereexposure to different levels of cobalt occurred for greater that 14 days but less one year. Basedon these studies, an individual might experience gastrointestinal upset from consuming the waterfrom the contaminated creeks. These gastrointestinal effects may include nausea, vomiting, anddiarrhea [14].

    Copper

    An individual consuming water from the creek may experience signs of gastrointestinal upsetsuch as diarrhea, nausea, vomiting, and abdominal pain and a metallic taste in their mouth at theconcentration of copper detected in the contaminated creeks [15].

    Iron

    Elevated concentrations of iron are commonly found in water supplies. Most elevatedconcentrations of iron are considered to be a nuisance because of the bad taste and staining. Anindividual might experience slight gastrointestinal upset (vomiting) from consuming water fromthe 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 atthe reported concentration of lead [17].

    Manganese

    There are no adverse health effects expected to occur from ingestion of the surface water in thecreeks 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 anindividual consuming water from the creeks as a result of exposure to elevated levels of nickel inthe surface water [19].

    Zinc

    Several studies have indicated that symptoms of gastrointestinal distress have been reported afterindividuals consumed solutions containing zinc at the exposure dose that individuals mightencounter if they consumed two liters from the contaminated creeks. These gastrointestinaleffects included vomiting, diarrhea, and abdominal cramps [20].

    B. Health Outcome Data Evaluation

    There were no relevant health outcome data to review for this site.

    C. Community Health Concerns Evaluation

    ATSDR was unable to identify any community health concerns related to the site.



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