1 Chapter 6

Chapter 6—Impacts of historical mining in the Coeur d’Alene River BasinBy Laurie S. Balistrieri1, Stephen E. Box1, Arthur A. Bookstrom1, Robert L. Hooper2, and J. Brian Mahoney2

Pathways of Metal Transfer from Mineralized Sources to Bioreceptors: A Synthesis of the Mineral Resources Program’sPast Environmental Studies in the Western United States and Future Research Directions

BACKGROUNDMining began in the late 1880s in the

Coeur d’Alene mining district in north-ern Idaho (fig. 1). Although only twomines, the Galena and Lucky Friday,currently are operating, more than 90historical mines exist in this region(Bennett and others, 1989). Most of themines are along the South Fork of theCoeur d’Alene River and its majortributaries (Bennett and others, 1989).Total production records indicate thatthis district ranks among supergiants(top 1 percent of world producers) forsilver (34,300 metric tons Ag) and lead(7,290,000 metric tons Pb) and amonggiants (top 10 percent of world produc-ers) for zinc (2,870,000 metric tons Zn)(Long, 1998a, 1998b).

Ore deposits in the district aresteeply dipping quartz veins and sider-ite (FeCO

3) veins containing

stratigraphically controlled Pb-Zn-Ag

ore shoots in Precambrian rocks of theBelt Supergroup (Fryklund, 1964;Hobbs and others, 1965; Zartman andStacey, 1971; Bennett andVenkatakrishnan, 1982; Leach andothers, 1988; Criss and Fleck, 1990).The veins are separated into two majortypes by ore mineralogy: (1) lead- andzinc-rich veins having argentiferousgalena (PbS) and sphalerite (ZnS) and(2) silver-rich veins having argentifer-ous tetrahedrite [(Cu, Ag)

10(Fe,

Zn)2(As, Sb)

4S

13] and minor galena and

sphalerite. The vein types are spatiallyseparated, may represent one or twoages of mineralization, and were depos-ited from fluids of metamorphic origin(Leach and others, 1998; Long, 1998a).Pyrite (FeS

2) is ubiquitous but variable

in abundance in the veins. Most veinscontain small amounts of chalcopyrite(CuFeS

2). Minor minerals include

arsenopyrite (FeAsS) and pyrrhotite1United States Geological Survey2University of Wisconsin Eau Claire

CONTENTSBackground 1Discussion of mining impacts 3 What is known about the distributions, con-

centrations, and speciation of Pb andZn in the Coeur d’Alene River basin? 3

Particulate lead. 3 Dissolved zinc 4 Solid-phase speciation 5

What is known about the processes that mobi-lize Pb and Zn from their sources andthen act to physically andbiogeochemically redistribute them? 7

Physical processes 7 Biogeochemical processes 8 Modeling of coupled physical and bio-

geochemical processes 10 What is known about impacts of Pb and Zn to

biota, and can specific processes that in-fluence bioavailability be identified? 12

What are the major gaps in knowledge re-maining from this research? 13

Acknowledgments 14References 14

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(Fe1-x

S). Host rocks are primarilyquartzite and argillite, which containsome interbedded carbonate-bearingrocks. Studies at the Lucky FridayMine indicate that wall rocks aroundveins are altered and typically contain10 to 15 percent carbonate minerals.Concentric zonation with respect tothree carbonate minerals [siderite(FeCO

3), ankerite [CaFe(CO

3)

2], and

calcite (CaCO3)] is common in the

altered wall rocks (Gitlin, 1986). Thepredominant gangue minerals aresiderite and quartz. The absolute andrelative abundances of sulfide andgangue minerals vary significantlybetween different vein systems.

Milling and ore concentration prac-tices varied over time in the districtbecause of changing technology andeconomics. Early ore separation meth-ods, which included coarse crushingand gravity (“jig”) mineral separationmethods, were not very efficient. Jigtailings produced before 1915 rangedfrom coarse gravel to fine powder andwere still very rich in metals. Develop-ment of more efficient flotation meth-ods between 1915 and 1925 resulted intailings with finer grain size (fine sandand finer) and lower metal concentra-tions. Most tailings were deposited

directly into the Coeur d’Alene Riverand its tributaries before environmentalregulations required the installation oftailings ponds in 1968. A preliminaryaccounting by Long (1998b) has esti-mated that 56 million metric tons oftailings containing 2,200 metric tons ofAg, 800,000 metric tons of Pb, and atleast 650,000 metric tons of Zn weredumped into the river system. Streamtransport, especially during major floodevents, has redistributed and continuesto redistribute metal-enriched sedimentfrom its sources for distances of morethan 240 km downstream throughoutthe channel of the South Fork and mainstem of the Coeur d’Alene River andtheir floodplains, into Lake Coeurd’Alene, and into the Spokane River(Horowitz and others, 1993; Horowitzand others, 1995; Bookstrom andothers, 2001; Box and others, 2001).Because the river gradient is steeperand the flow faster in the upper Coeurd’Alene River system, the major reposi-tories of the discharged mine tailingswere the channel and floodplain of thelower Coeur d’Alene River (that is,between Cataldo and Harrison) andLake Coeur d’Alene.

The Bunker Hill lead smelter inKellogg (see fig. 1) operated between

1917 and 1982 (Bennett and others,1989). This smelter released more than3,300 metric tons of Pb to the atmo-sphere between 1965 and 1981. Anarea of 54 km2 surrounding the smelterwas listed by the U.S. EnvironmentalProtection Agency (EPA) as one of thenation’s largest Superfund sites in1983 (U.S. Environmental ProtectionAgency, 1994). The listing wasprompted, in part, by very high levelsof Pb in the blood of children living inKellogg. A Natural Resource Damages(NRD) lawsuit filed by the Federalgovernment and two Native Americantribes is awaiting a decision after 2months of court testimony in 2001.The EPA completed a 3-year RemedialInvestigation/Feasibility Study (RI/FS)for the entire Coeur d’Alene Basin in2001. The proposed plan, in its publiccomment period as of May 2002,recommends a 30-year, $300 millionremedial program as the first incre-ment of a longer remediation schedule.EPA is expected to issue a Record ofDecision laying out its remediationplan in mid-2002. The State of Idahohas completed some remediationprojects and is currently doing severalmore within the district but outside ofthe Superfund site.

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Although our data encompass awide range of elements, the followingdiscussion of our work focuses on thebehavior of Pb and Zn in the near-surface environment because of theirimportance to environmental andhealth issues in the Coeur d’AleneRiver basin. As discussed in the intro-ductory chapter (ch. 1), we examinethe results of our work in light of fourquestions:

1. What is known about the distribu-tions, concentrations, and specia-tion of Pb and Zn in this riverbasin?

2. What is known about the processesthat release Pb and Zn from theirsources and then act to physicallyand biogeochemically redistributethem?

3. What is known about the impactsof Pb and Zn on biota and can weidentify specific processes thatinfluence bioavailability?

4. What additional work needs to bedone to provide a more thoroughunderstanding of Pb and Zn cy-cling in this basin?

Our work was done as part of theCoeur d’Alene Project that was fundedprimarily by the Mineral ResourcesProgram of the U.S. Geological Survey.

The EPA and U.S. Fish and WildlifeService provided supplemental funding.

DISCUSSION OF MININGIMPACTS

What is known about the distribu-tions, concentrations, and specia-tion of Pb and Zn in the Coeurd’Alene River basin?

Particulate Lead Pb exists primarily in the particulate orsolid phase rather than the dissolvedphase. This is because of the low solubil-ity of Pb minerals and the high affinity ofdissolved Pb for metal oxide particles atneutral pH. Health problems in the basinfor humans and wildlife are linked tohigh concentrations of particulate Pb insurface soils and sediment and to inges-tion of those particles. Elevated concen-trations of particulate Pb are associatedwith soils that formed over mineralizedrocks in the area (Gott and Cathrall,1980), tailings from mills that processedthe mineralized rock (Long, 1998b), andatmospheric fallout from smelters thatoperated in the mining district (U.S.Environmental Protection Agency, 1994).There are no new sources of particulatePb from smelters or tailings today be-

cause of closure of the smelters andenvironmental regulations that prohibitthe dumping of tailings into rivers.However, historically produced particu-late Pb from smelter fallout and milltailings is constantly being redistributedby wind and water. Because Superfundwork focused on cleaning up smelterfallout in houses and yards, the biggestremaining challenge is grappling with theenvironmental and health impacts offluvially distributed tailings.The origin of the fluvially depositedtailings is the historical milling andprocessing of ore within the district andsubsequent disposal of tailings into theriver system. The concentration ofmetals in tailings from mills in theCoeur d’Alene mining district decreasedirregularly through time as ore concen-tration methods improved (fig. 2).Gravity separation or jigging was the oreconcentration method used between1885 and 1925. Data from the historicalMorning Mill, the remnants of which arejust west of Mullan, indicates thattailings contained between 4 and 9percent Pb and Zn during this time (fig.2). Flotation methods, used between1925 and 1968, produced tailings con-taining lower metal concentrations (<1.5percent Pb and Zn) (fig. 2).

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The distribution of Pb as a function ofdepth in the sediments of the Coeurd’Alene River valley reflects the onset ofmining and history of milling practiceswithin the district (Bookstrom andothers, 2001; Box and others, 2001).Before mining began in the late 1880s,the concentration of Pb was <30 ppm inthe silty clay and fine sand of the basin(Bookstrom and others, 2001). Similarconcentrations are observed today in thedeepest portion of cores collected fromtransects across the river channel atKillarney (between Rose Lake andHarrison) and from the adjacent flood-plain (fig. 3). Changes in milling prac-tices over time also are reflected in thevarying concentrations of Pb with depthacross this transect. Sediments mixedwith early jig tailings that were depos-ited before about 1925 have the highestconcentrations of Pb (up to 36,000 ppm).A sharp drop in Pb concentration to lessthan 10,000 ppm, followed by a gradualupward decrease in Pb contents to 3,000-5,000 ppm, mark sediments from the eraof flotation methods. A gradual upwardcoarsening trend from silt at the base tomedium sand at the top is typical of theriver channel and bank deposits. Deposi-tion rates are still high on the river banks(average of 0.8 cm/yr) and little, if any,

diminution of sedimentation rate ormetal content in river bank or LakeCoeur d’Alene sediments has been notedsince the dumping of tailings dumpinginto the river was stopped in 1968(Horowitz and others, 1993; Box andothers, 2001).

In sediments finer than 175 mm in thebed of the Spokane River, the Pb contentranges from background concentrations(<30 ppm) to about 2,500 ppm, whereasZn concentrations vary from about 50 to5,000 ppm (fig. 4). A mixing modelsuggests these sediments are composedof three types of material that havedifferent sources: (1) background mate-rial with low Pb (20 ppm) and low Zn(50 ppm) concentrations, (2) material,possibly an authigenic flocculent, that ispoor in Pb (50 ppm) and rich in Zn(5,000 ppm), and (3) material derivedfrom the Coeur d’Alene River that hasmoderately high concentrations of bothPb (2,500 ppm) and Zn (4,000 ppm)(Box and Wallis, 2002).

Calculations of the volume of sedimentand associated Pb in various areas of theriver basin were recently done using digitalmaps of the South Fork and lower Coeurd’Alene River and chemical analyses ofmany sediment samples (Bookstrom andothers, 1999; Bookstrom and others, 2001;

Box and others, 2001). These calculationsindicate that there are 200,000±100,000metric tons of Pb in the South Fork drain-age basin, 250,000±62,000 metric tons inthe lower Coeur d’Alene River valleybetween Cataldo and Harrison, and292,000±145,000 metric tons in LakeCoeur d’Alene. Estimates have not yetbeen made for the North Fork drainagebasin or the Spokane River. About 99percent of the Pb contained in thesesediments was added as a result of mining-related activities. Of the Pb in the lowerCoeur d’Alene River valley, approximately59 percent is in the floodplain, 37 percentin the river channel, and 4 percent in theriverbanks. The estimated sum of Pb addedto sediments of the South Fork Rivervalley, Coeur d’Alene River valley, andLake Coeur d’Alene (739,000 + 305,000metric tons) amounts to about 87 percentof the estimated Pb (850,000 + 10,000metric tons) that was dumped into tribu-tary streams by the mills in the miningdistrict.

Dissolved Zinc

Although large amounts of particulateZn reside in the Coeur d’Alene Riverbasin, it is the dissolved form of Zn thatgoverns water quality in this regionbecause of its impact on the health of

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biota, particularly fish. Because of thisimpact, we compare concentrations ofdissolved Zn observed in the basin to theCriterion Continuous Concentration(CCC) for Zn, which is the highestconcentration of total recoverable Zn towhich aquatic life can be exposed for anextended period of time (4 days) withoutdeleterious effects (U.S. General Ser-vices Administration, 1999). Within thebasin, total recoverable Zn in watersamples typically is equal to dissolvedZn (Brennan and others, 2000; Brennanand others, 2001). The CCC for Zn inIdaho is a function of the hardness of thewater (U.S. General Services Adminis-tration, 1999). For example, for a rangein hardness of 15 to 65 mg/L, as ob-served in the Coeur d’Alene River, thecorresponding CCC for Zn ranges from21 to 73 mg/L (U.S. General ServicesAdministration, 1999). A water qualitycriterion for pH has also been set andranges from 6.5 to 9 for freshwater (U.S.Environmental Protection Agency,1999).

Dissolved Zn concentrations areplotted as a function of pH in figure 5for different types of water (adit drain-age, ground water from deep wells,porewater in the upper 30 cm of water-saturated sediments, water from tailings

seeps, and river water) affected by oredeposits or mining wastes within theCoeur d’Alene River basin. Both pH anddissolved concentrations of Zn showlarge variations, and many samples,particularly of ground water, do not meetwater quality criteria (Mink and others,1971; U.S. Geological Survey, 1973;McCulley Frick and Gilman, 1994;Balistrieri and others, 1998; GolderAssociates, 1998; TerraGraphics Envi-ronmental Engineering, 1998; Balistrieriand others, 2000; McCulley Frick andGilman, 2000). Values of pH range froma low of 2.72 at the Kellogg Tunnel (aditdrainage) to a high of 9.1 in the Coeurd’Alene River. Dissolved Zn concentra-tions range from 1.2 mg/L to 759 mg/L,and vary significantly at near-neutral pHvalues. Table 1 summarizes the rangeand median values for pH and dissolvedZn concentrations in the various waters.Except for water from the KelloggTunnel, ground water under tailings-bearing floodplain sediments and tail-ings piles has the lowest pH values andhighest dissolved Zn concentrations.Porewater in metal-contaminated sedi-ment mostly tends to be slightly acidic(median pH = 6.57) and can have moder-ately high dissolved Zn concentrations(up to 70 mg/L). Most adit drainage,

except from the Kellogg Tunnel, hasslightly alkaline pH values (median pH= 7.34) and moderately high dissolvedZn concentrations (up to 58 mg/L).Water from rivers is mostly near neutraland tends to have the lowest dissolvedZn concentrations, although the medianvalue is still above the CCC.

Solid-phase speciation

We have conducted two studies on thespeciation of metal-enriched particles inthe Coeur d’Alene River valley. Theintent was to look at changes in mineral-ogy and geochemical availability ofparticulate Pb and Zn as they are dis-persed from their primary sources assulfide minerals (galena and sphalerite)in the ore deposits and to determine howthe redox characteristics of the deposi-tional environment influence the miner-alogy and geoavailability of Pb and Zn.Our conclusions are based on mineral-ogical and geochemical leach studies ofthe particles.

The first study looked at the specia-tion of Pb in particles from paired sitesat three locations within the miningdistrict. At each location, the paired sitesare the floodplain, which containstailings from the jig era, and thenearby river channel. Both types of

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site are oxidizing environments.Mineralogical (R.L. Hooper and C.Rowe, unpublished data, 2000) andleach data using the methods ofGasser (Gasser and others, 1996) forthese particles are shown in table 2.The Pb, Fe, and Mn contents of thesesamples vary substantially, consider-ably higher concentrations generallyoccurring in sediment from the flood-plain. The mineralogical data indicatethe importance of Fe and Mn oxidesas host phases for Pb (also see fig. 6)and, in some cases, the formation ofsubstantial amounts of Pb carbonatesand sulfates. Trace amounts ofsphalerite are present in all samples.The sequential extraction data are inaccord with the mineralogical data inthat they indicate large fractions of Pbassociated with Fe and Mn oxides(that is, in the EDTA or HNO

3 leach)

or, in the case of sample 205, angles-ite (that is, in the MgCl

2 leach).

Results from the leach simulatinggastric conditions suggest that amajor fraction of Pb in most of thesesamples would be mobilized in thehuman stomach. This work indicatesthat the speciation of particulate Pbchanges from a sulfide mineral to Pbcarbonates and sulfates or Pb associ-

ated with Fe and Mn oxides within ashort distance (<10 km) from the oredeposits. These results are consistentwith observations of mineralogicalchanges in Pb downstream from lead-zinc-fluorite-barite deposits in north-east England (Hudson-Edwards andothers, 1996).

The second study looked at thespeciation of Pb and Zn in particles as afunction of depth from four differentenvironments (river bed, levee banks,wetlands, and lateral lakes) in the lowerCoeur d’Alene River valley using acombination of mineralogical andchemical techniques (SEM, TEM, andsequential leaches) (Hooper andMahoney, 2000, 2001). Care was takento maintain the redox characteristics ofthe samples during collection, storage,and analyses. A sequential extractionmethod (Tessier and others, 1979) wascalibrated by determining the mineral-ogy after each extraction step (fig. 7).The individual steps in the sequentialextraction scheme generally are notspecific for given mineral phases.However, patterns of metal release,considering all of the extraction stepsalong with the calibration results,provide information about the domi-nant phases in the samples.

Periodic flooding transports pri-mary ore minerals (sulfides) andsecondary mineral phases (oxides andcarbonates) from upstream tailingsdeposits into the lower river valley.Preliminary results of our analyses ofparticles in the lower river valleysuggest that their mineralogy is verycomplex and that they contain consid-erable amounts of amorphous andnanocrystalline material. The fate ofparticles, which may involve mineraldissolution, metal mobilization andmigration, and mineral precipitation,depends on the redox characteristics,permeability, organic content, andmicrobial activity of the depositionalenvironment. Particles in the bed ofthe river below the sediment-waterinterface are in a reducing environ-ment, which acts as a sink for detritalsulfides and carbonates (fig. 8).Authigenic Fe, Pb, and Zn sulfidesappear to form near the sediment-water interface. Because of water-level changes throughout the year,particles in the levee environment,near the edge of the river, cyclebetween dry and wet conditions. Thisresults in oxidizing zones containingoxide-coated grains interspersed withreducing zones dominated by detrital

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and authigenic carbonate and sulfidephases. Unexpectedly, detrital sphaler-ite is present in oxidized levee samples,indicating that some fraction of thetotal amount of the mineral is resistantto oxidation. Sediment at the top oflevees resides in oxidizing environ-ments, and samples from these environ-ments, contain small amounts of detritalgalena (PbS) and greater amounts ofcerrusite (PbCO

3) and Pb-Fe-Mn oxides

(fig. 8). In some samples Pb is associ-ated with Mn oxides, and in others it isassociated with Fe oxides. Zn existsprimarily with Fe-Mn oxides. Thewetland environment is anoxic, andmost of the particulate Pb and Zn existas microcrystalline and nanocrystallineto amorphous authigenic sulfidesassociated with biofilms, rootlets, andbacteria. Anoxic conditions also exist inthe sediments of the lateral lakes.Particles in the lateral lakes containnanocrystalline inorganic and biogenicsulfides in the upper third of the metal-enriched sediment and increasingamounts of silt-size detrital sulfides(especially sphalerite) closer to thepremining surface. In both the wetlandand lateral lake environments, micro-bial activity is extremely effective inremoving metals from the water and

producing a nanocrystalline biofilm onparticles that is characterized by ZnSand nonstoichiometric PbS, FeS, andmixed metal sulfides.

What is known about the pro-cesses that mobilize Pb and Znfrom their sources and then act tophysically and biogeochemicallyredistribute them?

Physical processes

Several physical processes play impor-tant roles in determining the distributionand concentration of Pb and Zn in theCoeur d’Alene River basin, includingthose involved in historical miningpractices; hydrologic transport andseasonal fluctuations in water levels;sorting of particles by size fractionsduring flood events; mixing of differentsource waters; and transport of dissolvedmetals across the sediment-water inter-face by molecular diffusion. Each ofthese is discussed here.

The milling practices and subsequentdisposal of tailings into the river systembefore 1968 were important factors indetermining the present day geochemicalcharacteristics of the basin. Long (1998b)estimated that 109 million metric tons ofmetal-enriched mill tailings were pro-

duced by jigging and flotation methodswithin the district. About 51 percent ofthose were disposed of in the Coeurd’Alene River and its tributaries, 37percent were placed in impoundments orused as stope fill, and 12 percent werestockpiled along the floodplain. Hydro-logic transport, especially during floodevents, resulted in sorting of this metal-enriched material and in the deposition offluvial tailings deposits not only withinthe mining district, but also throughoutthe lower Coeur d’Alene River valley, inLake Coeur d’Alene, and in the SpokaneRiver. There is a potential long-termsource of metal-enriched material to thefloodplain, Lake Coeur d’Alene, and theSpokane River because a large fraction ofPb (about 41 percent of Pb in the lowerCoeur d’Alene River valley) resides or isstored in the river channel and riverbanks(Box and others, 2001) and is subject tomovement during high flows.

Pb and Zn data for particles in theriver bed and on the levee banks (Boxand others, 2001) and for particlessuspended in the water of the Coeurd’Alene River during two flood events(Box and others, in press) are used toillustrate the importance of sources ofsediment to the river (fig. 9).Riverbanks and natural levees of the

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Coeur d’Alene River and alluvialterraces of the South Fork have lowerZn than Pb concentrations because Znis preferentially leached from sedi-ments stored in oxidizing environ-ments. In contrast, bed sediments in theriver channel are more enriched in Znthan Pb. The major rain-on-snow floodof 1996 began suddenly, when LakeCoeur d’Alene was low and hydraulichead between the river and the lake washigh. Floodwaters ran red with oxidizedsuspended sediment, and Zn/Pb ratios ofsuspended sediment were less than one,indicating that most of the suspendedsediment was mobilized from oxidizingenvironments. By contrast, the major1997 spring runoff flood began gradu-ally and continued for about a month,with relatively clear waters in the upperbasin, sluggish currents along the Coeurd’Alene River, and floodwater backingup from Lake Coeur d’Alene as itoverfilled. During this 1997 and previ-ous spring runoff floods, Zn/Pb ratios ofsuspended sediment were greater thanone, indicating that fines, winnowed outof riverbed sediment, predominated oversediment from oxidizing environments.In both events, however, sandyriverbank deposits were derived frommobilization of nearby bed sediments.

Another physical process that influ-ences the distribution of elements ismixing of different source waters. Aditdrainage within the district that is en-riched in dissolved elements mixes withrivers and creeks that have lower concen-trations of elements (Balistrieri andothers, 1998). The North Fork of theCoeur d’Alene River supplies less metal-enriched water and sediment to the lowerCoeur d’Alene River than the South Forkat their confluence above Cataldo. Also,variations in metal loading along theSouth Fork and its tributaries suggestmixing of surface water with more metal-enriched ground water (Barton, 2002).

Dissolved Zn, other metals, and nutri-ents can be supplied to Lake Coeurd’Alene by inflowing rivers and bytransport across the sediment-waterinterface (benthic flux). Benthic fluxeswere determined from concentrations inthe water at the bottom of the lake and inporewater in the sediment using Fick’sFirst Law and time-series data from in-situ benthic flux chambers (Balistrieri,1998; Kuwabara and others, 2000). Theresults indicate that transport of dissolvedelements and species is controlled bymolecular diffusion and that the magni-tudes of the benthic fluxes of dissolvedZn, Cd, phosphate, and nitrogen species

into the water column of the lake aresimilar to fluxes supplied to the lake bythe St. Joe and Coeur d’Alene Rivers.

Biogeochemical processes

Water-rock interactions act to mobilizeand redistribute elements within the riverbasin. Microorganisms mediate many ofthese reactions. Oxidation reactionsinvolving primary sulfide minerals in theore deposits result in the release ofmetals, sulfate, and in some cases (forexample, pyrite oxidation) acid to thewater. This acidity can be neutralized bythe dissolution of buffering minerals,primarily carbonates such as calcite orankerite. The relative molar amounts ofpyrite and carbonate minerals in thedeposits and host rocks that react or thereacting pyrite-to-calcite ratio can bepredicted from the composition of drain-age from adits (Balistrieri and others,1999; Balistrieri and others, 2002). Thepredicted reacting pyrite-to-calcite ratios(assuming precipitation of ferrihydrite)for deposits in the Coeur d’Alene miningdistrict range from 0.02 to 0.5 for near-neutral drainage to about 1 for the acidicdrainage from the Kellogg Tunnel at theBunker Hill mine site (fig. 10). Data fordrainage from other polymetallic vein

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deposits in the Colorado Mineral Belt andthe Humboldt River Basin, Nevada, arealso shown in figure 10 for comparison(Plumlee and others, 1993; Plumlee andothers, 1999; Nash, 2000). Theoretically,neutralization of acid generated duringoxidation of one mole of pyrite requiresbetween 2 and 4 moles of calcite (that is,reacting pyrite-to-calcite ratios between0.25 and 0.5) (Cravotta and others, 1990).Data for water draining polymetallic veindeposits in Idaho, Colorado, and Nevadaare consistent with the theoretical predic-tions, showing drainage pH values thatrange from near neutral to alkaline whenreacting pyrite-to-calcite ratios for thedeposits are <0.3.

The precipitation of secondary miner-als such as carbonates (cerrusite andsmithsonite), sulfates (Zn sulfate andanglesite), and oxides (Fe and Mnoxyhydroxides and Feoxyhydroxysulfates) and adsorption ofdissolved elements onto the secondaryoxide phases occur after mobilization ofspecies from the primary sulfide miner-als. The identity and composition of theseprecipitates were determined usingmineralogical, chemical, and modelingtechniques. We conducted several sets ofexperiments that mixed surface waterwith ground water, adit drainage, or

porewater and assessed the ability ofthermodynamic models to predict theprecipitation of mineral phases andadsorption of metals onto metal oxidephases (Paulson and Balistrieri, 1999;Tonkin and others, 2002) usingPHREEQC (Parkhurst and Appelo, 1999)and a database containing sorptionparameters for elements onto hydrousferric oxide (Dzombak and Morel, 1990).

Many important conclusions resultedfrom this work. First, thermodynamicmodeling successfully predicted observedpH changes, precipitation of ferrihydrite,and removal of Cd, Cu, Pb, Zn, and, insome cases, As in the mixing experiments(fig. 11). Second, the relative efficiencyof removal of metals by adsorption ontoFe oxide is Pb>Cu>> Zn~Cd. Third, Feoxide is a stronger adsorbent than Aloxide, and adsorbed organic matter is animportant adsorbent for Zn and Cd.Fourth, the adsorption characteristics offerrihydrite and schwertmannite can bedescribed by the same set of adsorptionparameters (that is, site density, surfacearea, and adsorption complexationconstants). Fifth, more metal is re-moved by adsorption if Fe oxides thatprecipitate during the mixing of acidicground water and near-neutral surfacewater remain suspended in the water

(transported scenario) rather than beingseparated from the water and remainingin the aquifer (retained scenario) alonga flow path. Because pH increasesalong the flow path, greater metalremoval occurs in the transported thanin the retained case because the zone ofprecipitation of Fe oxide, which occursat a lower pH, is not separated from thezone of adsorption of metals onto Feoxide, which occurs at a higher pH.

The influence of organic matterdiagenesis on redox state has beendemonstrated in porewater studies in thesediments of Lake Coeur d’Alene and insediments along the river’s edge and inmarshes of the lower Coeur d’AleneRiver valley (Balistrieri, 1998; Balistrieriand others, 2000). Organic matterdecomposition occurs using a thermody-namically predictable sequence ofoxidants (oxygen, nitrate, Mn oxide, Feoxide, and sulfate) and results in redoxconditions that range from oxic tosuboxic, or to anoxic and sulfidic asdepth increases in the sediment (Froelichand others, 1979). Redox state, in turn,influences the mobility of elements,particularly Zn, because of the release ofassociated elements during reduction ofoxide phases under suboxic conditionsand the insolubility of authigenic metal

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sulfide phases under anoxic and sulfidicconditions. Porewater data from sedi-ments in the lower Coeur d’Alene Rivervalley suggest that Zn is more mobile(that is, higher concentrations inporewater) under oxidizing than underreducing conditions, most likely becauseof formation of authigenic Zn sulfidesunder anoxic and sulfidic (reducing)conditions.

Modeling of coupled physical andbiogeochemical processes

Metal distributions and concen-trations in the environment are a resultof the interaction of many physicaltransport processes and biogeochemicalreactions. Understanding the dominantprocesses is critical for successful designof remediation activities and for long-term management of ecosystems af-fected by human activities. Developmentof mathematical models that describemetal cycling in such systems synthe-sizes our understanding of how thesystem works by identifying and de-scribing dominant processes and poten-tially allows for sensitivity tests to assesshow a system might respond to perturba-tions. Models can also assess our under-standing of system behavior by compar-ing observations and predictions during

and after remediation activities. Onesuch model describing the behavior ofdissolved Zn in Lake Coeur d’Alene isdiscussed here.

We used a mass balance approach toexamine various processes that controlthe concentration of dissolved Zn inLake Coeur d’Alene (L.S. Balistrieri andP.F. Woods, unpublished data, 2002).Lake Coeur d’Alene is treated as asingle, completely mixed system (that is,a one-box model) (fig. 12). The follow-ing equation describes changes in dis-solved Zn concentrations in the lake as afunction of time (dC

Zn/dt):

dCZn

/dt = IZn

+ PZn

- OZn

- RZn

(1)

where IZn

accounts for all external inputsof dissolved Zn to the lake, P

Zn accounts

for all internal sources of dissolved Znto the lake, O

Zn accounts for fluxes of

dissolved Zn out of the lake, and RZn

accounts for internal removal of dis-solved Zn from the water column. Allterms have units of mg/L per day.

Dissolved Zn enters the lake throughriver inlets (Coeur d’Alene, St. Joe, andSt. Maries Rivers) and leaves through asingle outlet (Spokane River). Theseprocesses are depicted by the I

Zn and O

Zn

terms in equation 1. Benthic fluxes of

dissolved Zn, represented by the PZn

termin equation 1, act as an additional sourceof dissolved Zn to the lake, whereasscavenging of dissolved Zn to particulateZn and sedimentation, depicted by R

Zn,

removes dissolved Zn from the watercolumn of the lake.

Calculations were done using thecomputer program AQUASIM (Reichert,1994), which allows for simulations ofaquatic systems. Discharge and dis-solved concentrations in the rivers forthree water years (WY1999-2001; notethat water year 2000 runs from October1, 1999 to September 30, 2000) wereused (Brennan and others, 1999;Brennan and others, 2000; Brennan andothers, 2001) (fig. 13). Discharge duringthe 3 water years was variable; WY2000had 90 percent of the discharge ofWY1999, whereas WY2001 had only 37percent of the discharge of WY1999.

Several assumptions were made in themodeling:

1. The inflow is equal to the outflow;in other words, the volume of thelake does not change over time.This assumption is a good approxi-mation because the lake volumechanges by less than 9 percentthroughout the year (Woods andBeckwith, 1997).

11 Chapter 6

2. The volume of the lake is 2.8 x 1012

L and the surface area of the lake-bottom sediment is 1.08 x 1012 cm2

(Woods and Beckwith, 1997).3. The exchange of dissolved Zn

across the sediment-water interfaceis by molecular diffusion; therefore,a molecular diffusion coefficient isused to describe this process. Thisassumption is supported by thework of Kuwabara and others(2000). The average value of themolecular diffusion coefficient ofdissolved Zn at bottom watertemperatures in Lake Coeurd’Alene is 0.279 cm2 per day (Liand Gregory, 1974; Balistrieri,1998).

4. A range in the concentration ofdissolved Zn in the porewater justbelow the sediment-water interfaceis used to calculate the input ofdissolved Zn to the lake by benthicfluxes. Dissolved Zn concentrationsof 1,070 (25th percentile), 1,210(median), and 1,650 (75th percen-tile) mg/L are used, based on 10published values (Balistrieri, 1998;Kuwabara and others, 2000); theseconcentrations do not vary season-ally in the model calculations.

5. Scavenging of dissolved Zn to

particulate Zn and subsequentsedimentation is described by afirst-order rate coefficient (k

scav),

and scavenging of dissolved Znderived from the riverine input isthe same as scavenging of dissolvedZn derived from the benthic fluxsource. In other words, there is nodifference in the chemical behavioror speciation of dissolved Zn fromthe two sources.

Model results depend on the formula-tion of the model (for example, theprocesses considered and their param-eterization) and the measured data thatare used. Assuming that all of the impor-tant processes are incorporated into themodel, then the most reliable data arethe physical characteristics of the systemsuch as lake volume and surface area ofsediment, the measured discharge anddissolved Zn concentrations for theinflows and outflow, and the moleculardiffusion coefficient for dissolved Zn.The least well known data are theporewater concentrations of dissolvedZn, which determine the benthic flux,and the parameterization of the removalof dissolved Zn from the water column.Little information is available on spatialvalues and no information on seasonalvalues of dissolved Zn in the porewater

just below the sediment-water interfacein Lake Coeur d’Alene. The removal ofdissolved Zn from the water column isassumed to be by transformations to theparticulate phase and settling of par-ticles. No sediment trap data are avail-able to support this assumption. Inaddition, this removal is assumed tofollow first-order kinetics. Limitedinformation from in situ microcosmstudies in lakes suggests that removal ofdissolved metals from the water columnfollows a first-order rate equation(Santschi and others, 1986; Andersonand others, 1987).

Model results indicate that the relativeimportance of inputs of dissolved Zn toLake Coeur d’Alene from rivers andbenthic flux varies through the year andfrom year to year (fig. 14A,B). Thebenthic flux contribution to dissolved Znconcentrations in the lake was largerthan the river contributions duringOctober of the first two water years(WY99-WY00); otherwise, contribu-tions from the inflowing river domi-nated. During WY01, which was a low-discharge year, the supply of dissolvedZn to the lake by benthic flux dominatedduring the first 6 months (Octoberthrough March), whereas the supplyfrom inflowing rivers was dominant

12 Chapter 6

during the subsequent 4 months (Aprilthrough July). Benthic flux was theprimary input of dissolved Zn to thelake for the remainder of the wateryear. Low discharge results in lessinput of dissolved Zn to the lake fromrivers and a higher proportion of inputfrom benthic flux. In addition, therelative importance of sources ofdissolved Zn to the lake will changeas cleanup efforts within the miningdistrict and lower Coeur d’AleneRiver valley proceed.

Values of the first-order scavengingrate coefficient that are needed to fitthe measured dissolved Zn concentra-tions in the outflow (Spokane River)range by a factor of 46, from 0.0005to 0.023 per day (f ig. 14C). Thehighest values of this coefficient weredetermined in the third or fourthquarter of the water year and slightlyprecede the minimum in dissolved Znconcentration. For comparison, valuesof scavenging coefficients for dis-solved Zn from whole-lake experi-ments and microcosm studies usingradiotracers range from 0.03 to 0.06per day (Santschi and others, 1986;Anderson and others, 1987). Thesevalues are at the high end of valuesdetermined by the modeling of dis-

solved Zn in Lake Coeur d’Alene.What processes are responsible for

variations in the scavenging rate coeffi-cient? Scavenging rate coefficientsencompass the partitioning of metalbetween dissolved and particulatephases and the settling velocity or fluxof particles (Sigg, 1985). Partitioningbetween dissolved and particulatephases can be described by a distribu-tion coefficient and is a function of theparticle type, particle concentration,pH, ionic strength, and temperature ofthe system. Scavenging rate coeffi-cients are largest when dissolved metalshave a strong affinity for particulatephases and the flux of particles in thesystem is large. Some insight intovariations of scavenging rate coeffi-cients for Zn is given by work done in alake in Switzerland (Sigg and others,1996). Although they examined arelatively pristine lake relative to LakeCoeur d’Alene (Lake Greifen, Switzer-land, where Zn concentrations are 0.65-2.6 mg/L), the chemical behavior of Znshould be similar in the two lakes.Using sediment trap data, they foundthat the sedimentation of Zn (or trans-formations from dissolved to particu-late phases and subsequent settling) wasrelated to sedimentation of algae and

manganese dioxide. Because primaryproductivity is seasonal, they observedcorresponding seasonal variations insedimentation of Zn. About 87 percentof the dissolved Zn that enters LakeGreifen is trapped within the lake, com-pared to 56 percent in Lake Coeurd’Alene. Sigg and others (1996) concludedthat biological mechanisms of uptake andbinding are significant for the removal ofdissolved Zn from the water column inLake Greifen. The largest scavenging ratecoefficients for dissolved Zn determinedfor Lake Coeur d’Alene occur duringperiods when the maximum in biologicalproductivity would be expected. Furtherwork is needed to understand the mecha-nisms and the role of biology in control-ling transformations of dissolved toparticulate Zn in Lake Coeur d’Alene.

What is known about impacts ofPb and Zn to biota, and can spe-cific processes that influencebioavailability be identified?

The health impacts of mining in theCoeur d’Alene River basin on humansand other biota are highly dependent onthe phase of the metal. The criticalphase for Pb is the particulate form,

13 Chapter 6

whereas for Zn it is the dissolved form.Some of the highest levels of Pb in

the blood of children in the UnitedStates were measured in the Coeurd’Alene mining district around theBunker Hill smelter and the eventualSuperfund site (f ig. 15). The primarypathway of Pb into human blood isingestion of Pb-enriched particlesthat are soluble in the stomach.Solubility of the particles depends onthe speciation of Pb in the solidphase (Ruby and others, 1992; Gas-ser and others, 1996). In 1974, oneyear after a f ire destroyed the airemission controls on the Bunker Hillsmelter stack, 98 percent of children1 to 9 years old in the area aroundthe smelter had blood Pb levels >40mg/dL (U.S. Environmental Protec-tion Agency, 1994). Emergencyresponse actions (for example, edu-cation about hygiene, smelter clo-sure, and yard remediation) resultedin lower blood Pb levels, most ofwhich are now below the maximumrecommended level of 10 mg/dL.However, recent studies of blood Pblevels in children living outside ofthe Superfund site, but within theCoeur d’Alene River basin, indicatethat about 15 percent of children

between the ages of 9 months and 9years have higher than recommendedlevels of Pb in their blood(TerraGraphics Environmental Engi-neering and others, 2001). Warningsof potential human exposure to highconcentrations of metals in sedimentand f ish and related health impactsare posted at recreational beachesalong the lower Coeur d’Alene River,Coeur d’Alene Lake, and SpokaneRiver.

High concentrations of Pb in surfacesediments within the basin and dis-solved Zn in rivers also have provedharmful to terrestrial and aquaticwildlife. The metal-enriched marsheswithin the lower Coeur d’Alene Rivervalley are prime resting and feedingareas for migratory birds, and deathsrelated to Pb poisoning during feedingin this area have been reported forwaterfowl (Beyer and others, 1998).High dissolved Zn concentrations inthe South Fork of the Coeur d’AleneRiver and its tributaries have preventedthe re-establishment of a viable fish-ery, despite attempts to improve fishhabitat in streams (T. Maret, unpub-lished data, 1999).

Factors that affect thegeoavailability and, ultimately,

bioavailability of Pb are linked to thespeciation of Pb in the solid phase,which depends on the redox conditionsof the depositional environment. Theimpact of Zn on biota depends on themobilization of this element frommetal-enriched tailings and subsequenttransport and reaction between groundwater and surface water.

What are the major gaps inknowledge remaining from thisresearch?

1. Quantitative and predictive dynamicmodels are needed that provide anunderstanding of the underlyingmechanisms controlling the trans-port, reaction, and fate of Pb, Zn,and other elements in the Coeurd’Alene River basin and other large-scale systems affected by miningactivities. Sensitivity tests with suchmodels would provide informationon the response of large-scalesystems to natural and human-induced perturbations, would iden-tify data gaps, and could be used todirect remediation and managementof the systems.

2. The interrelationships amongprocesses and factors responsible

14 Chapter 6

for chemical speciation, mobiliza-tion, and transport of Pb, Zn, andother elements in the environment(geoavailability) and the uptake ofPb, Zn, and other elements by biota(bioavailability) need to be furtherdefined.

3. The role of microorganisms indetermining chemical speciation,geoavailability, and bioavailabilityfor Pb, Zn, and other elementsneeds to be further evaluated.

ACKNOWLEDGMENTSRobert Seal, Michael Zientek, Tom

Frost, and Peter Vikre of the U.S. Geo-logical Survey provided comments on anearlier draft of this paper. Peter Stauffer’sediting of the manuscript helped im-prove its clarity.

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Balistrieri, L.S., 1998, Preliminary es-timates of benthic fluxes of dis-

solved metals in Coeur d’AleneLake, Idaho: U.S. Geological Sur-vey Open-File Report 98-793, 40 p.

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Balistrieri, L.S., Box, S.E.,Bookstrom, A.A., and Ikramuddin,M., 1999, Assessing the influenceof reacting pyrite and carbonateminerals on the geochemistry ofdrainage in the Coeur d’Alene min-ing district: Environmental Scienceand Technology, v. 33, no. 19, p.3347-3353.

Balistrieri, L.S., Box, S.E., Ikramuddin,M., Horowitz, A.J., and Elrick,K.A., 2000, A study of porewater inwater saturated sediments of leveebanks and marshes in the lowerCoeur d’Alene River valley, Idaho;sampling, analytical methods, andresults: U.S. Geological SurveyOpen-File Report 00-126, 62 p.

Balistrieri, L.S., Box, S.E., andBookstrom, A.A., 2002, Ageoenvironmental model for

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Barton, G.J., 2002, Dissolved cad-mium, zinc, and lead loads fromground-water seepage into theSouth Fork Coeur d’Alene Riversystem, Northern Idaho, 1999: U.S.Geological Survey Water-Re-sources Investigations Report 01-4274, 139 p.

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Bennett, E.H., Siems, P.L., andConstantopoulos, J.T., 1989, The ge-ology and history of the Coeurd’Alene mining district, Idaho, inChamberlain, V.E., Breckenridge,R.M., and Bonnichsen, B., eds.,Guidebook to the Geology of

15 Chapter 6

Northern and Western Idaho andsurrounding area, Idaho GeologicalSurvey Bulletin 28, p. 137-156.

Beyer, W.N., Audet, D.J., Morton, A.,Campbell, J.K., and LeCaptain, L.,1998, Lead exposure of waterfowlingesting Coeur d’Alene River ba-sin sediment: Journal of Environ-mental Quality, v. 27, no. 6, p.1533-1538.

Bookstrom, A.A., Box, S.E., Jackson,B.L., Brandt, T.R., Derkey, P.D., andMunts, S.R., 1999, Digital map ofsurficial geology, wetlands, anddeepwater habitats, Coeur d’AleneRiver valley, Idaho: U.S. GeologicalSurvey Open-File Report 99-548,121 p.

Bookstrom, A.A., Box, S.E., Campbell,J.K., Foster, K.I., and Jackson, B.L.,2001, Lead-rich sediments, Coeurd’Alene River valley, Idaho; area,volume, tonnage, and lead content:U.S. Geological Survey Open-FileReport 01-140, 57 p.

Box, S.E., and Wallis, J.C., 2002,Surficial geology along the Spo-kane River, Washington, and its re-lationship to the metal content ofsediments (Idaho-Washingtonstateline to Latah Creekconfluence): U. S. Geological Sur-

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Ikramuddin, M., and Lindsay, J.,2001, Geochemical analyses ofsoils and sediments, Coeur d’Alenedrainage basin, Idaho; sampling,analytical methods, and results: U.S. Geological Survey Open-FileReport 01-139, 206 p.

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Brennan, T.S., Lehmann, A.K., O’Dell,I., and Tungate, A.M., 1999, Waterresources data, Idaho, water year1998 Volume 2. Upper ColumbiaRiver Basin and Snake River Basinbelow King Hill: U.S. GeologicalSurvey Water-Data Report ID-98-2, 386 p.

Brennan, T.S., Campbell, A.M.,Lehmann, A.K., and O’Dell, I.,2000, Water resources data, Idaho,water year 1999 Volume 2. UpperColumbia River Basin and SnakeRiver Basin below King Hill: U.S.Geological Survey Water-Data Re-

port ID-99-2, 440 p.Brennan, T.S., Campbell, A.B.,

Lehmann, A.K., and O’Dell, I.,2001, Water resources data, Idaho,water year 2000, Volume 2. UpperColumbia River Basin and SnakeRiver Basin below King Hill: U. S.Geological Survey Water-Data Re-port ID-00-2, 402 p.

Cravotta, C.A., III, Brady, K.B.C.,Smith, M.W., and Beam, R.L.,1990, Effectiveness of alkaline ad-dition at surface mines in prevent-ing or abating acid mine drainagePart 1. geochemical considerations,in Skousen, J.G., Sencindiver, J.,and Samuel, D.E., eds., Proceed-ings of the 1990 Mining and Recla-mation Conference and Exhibition,p. 221-226.

Criss, R.E., and Fleck, R.J., 1990,Oxygen isotopic map of the giantmetamorphic-hydrothermal systemaround the northern Idahobatholith, U.S.A.: AppliedGeochemistry, v. 5, p. 641-655.

Dzombak, D.A., and Morel, F.M.M.,1990, Surface complexation mod-eling hydrous ferric oxide: NewYork, John Wiley & Sons, 393 p.

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16 Chapter 6

Heath, G.R., Cullen, D., Dauphin,P., Hammond, D.E., Hartman, B.,and Maynard, V., 1979, Early oxi-dation of organic matter in pelagicsediments of the eastern equatorialAtlantic; suboxic diagenesis:Geochimica et CosmochimicaActa, v. 43, p. 1075-1090.

Fryklund, V.C., Jr., 1964, Ore depositsof the Coeur d’Alene district,Shoshone County, Idaho: U.S. Geo-logical Survey Professional Paper445, 103 p.

Gasser, U.G., Walker, W.J., Dahlgren,R.A., Borch, R.S., and Burau,R.G., 1996, Lead release fromsmelter and mine waste impactedmaterials under simulated gastricconditions and relation to specia-tion: Environmental Science andTechnology, v. 30, no. 3, p. 761-769.

Gitlin, E., 1986, Wall rock geochemis-try of the Lucky Friday Mine,Shoshone County, Idaho: Seattle,University of Washington, Ph.D.dissertation, 224 p.

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Gott, G.B., and Cathrall, J.B., 1980,Geochemical exploration studies inthe Coeur d’Alene district, Idahoand Montana: U. S. GeologicalSurvey Professional Paper 1116, 63p.

Hobbs, S.W., Griggs, A.B., Wallace,R.E., and Campbell, A.B., 1965,Geology of the Coeur d’Alene dis-trict, Shoshone County, Idaho: U.S.Geological Survey Professional Pa-per 478, 139 p.

Hooper, R.L., and Mahoney, J.B.,2000, Constraining contaminanttransport; lead and zinc speciationin fluvial subenvironments, lowerCoeur d’Alene River valley, Idaho:Geological Society of America Ab-stracts with Programs, v. 32, no. 7,p. 125.

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and related activities on the sedi-ment trace element geochemistryof Lake Coeur d’Alene, Idaho,USA. Part I. surface sediments:Hydrological Processes, v. 7, p.403-423.

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17 Chapter 6

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Coeur d'Alene

Smelterville KelloggRoseLake

Cataldo

Bunker HillSuperfund site

Wallace

Osburn

Coeur d'Alene mining district

Mullan

Coeurd'AleneLake

North Fork

Harrison

St. Joe River

116°W

Burke

Coeur d'Alene River

SouthForkKingston

Spokane River

Washington0

0 10 KILOMETERS

10 MILESN

Elizabeth Park

47.5°N

OregonIdaho

Montana

Wyoming

AREA OF MAP

Figure 1.—Index map of the Coeur d’Alene River basin. The dark squares are towns.

20 Chapter 6

Figure 2.—Annual production in metric tons and percent metal content of tailings produced at the Morning Mill from 1895 to 1958. Unpublisheddata from K. Long, U.S. Geological Survey.

21 Chapter 6

Winter water level

Channel of Coeur d'Alene River

a b

c

b

d

Medium-grained sand: 3-4,000 ppm Pb

Interbedded fine sand and silt: 4-10,000 ppm Pb

Silt and very fine sand: 15-36,000 ppm Pb

Pre-mining sand and silt: < 30 ppm Pb

10 meters

5 m

eter

s

East West

Core location

abcd

SEDIMENT LAYERS ANDASSOCIATED LEAD CONTENTS

Summer water level

Figure 3.—Stylized cross section showing the Pb content of sediments in cores from the floodplain and channel of the Coeur d’Alene River near Killarney (between RoseLake and Harrison). Data from Box and others (2001).

22 Chapter 6

2,500

2,000

1,500

500

0

0 5 10 15

1,000

4,000

5,000

2,500

Figure 4.—Pb concentrations and Zn/Pb ratios in the <175 mm fraction of bed sediment in the Spokane River compared to resultsof a mixing model involving three different sources of sediment.

23 Chapter 6

Figure 5.—Dissolved Zn concentrations and pH values in river water, ground water, porewater, tailings seeps, and adit drainagein the Coeur d’Alene River basin. Also shown are water quality criteria for pH and Criterion Continuous Concentration (CCC) forZn, which is the highest concentration of total recoverable Zn to which aquatic life can be exposed for an extended period of time(4 days) without deleterious effects in Idaho water. See text and table 1 for data sources.

24 Chapter 6

Figure 6.—Scanning electron microscope (SEM) im-age and X-ray intensity maps of a single detrital sili-cate grain coated with Pb/Fe/Mn oxide from thesurficial floodplain soil in Smelterville Flats. A, SEMimage. B, X-ray intensity map of Pb. C, X-ray inten-sity map of Mn. Images suggest that Pb is primarilyassociated with Mn oxide.

Figure 7.—Calibration of a sequential extraction scheme based on the method of Tessierand others (1979) by mineralogical analyses after each extraction step of particlescollected in the Coeur d’Alene River basin.

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Figure 8.—Sequential extraction results for samples collected in the river channel, on top of levee banks, and in wetlands in the lower Coeur d’Alene River valley.

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Figure 9.—Comparisons of the Pb and Zn contents of suspended sediments during the spring floods in 1996 and 1997 in the Coeur d’AleneRiver basin. The 1996 flood was larger than the 1997 flood.

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Figure 10.—Comparisons between the predicted ratio of reacting pyrite-to-calcite minerals (considering pre-cipitation of ferrihydrite and calculated as pyritic SO4/(Ca + Mg) in drainage) and pH in drainage from polymetallicveins in the Coeur d’Alene mining district, the Colorado Mineral Belt, and Humboldt River Basin, Nevada. Seetext for data sources.

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Figure 11.—Comparison of measured and predicted values of pH, and of Pb adsorbed on Fe precipitates formed, during the mixing of Coeur d’Alene River water andporewater from metal-enriched sediments near the river’s edge in Cataldo, Smelterville Flats, Killarney, and Rose Lake. Errors bars on measured particulate Pb data arepropagated error in calculating particulate concentrations from initial and final dissolved Pb concentrations in the mixing experiments. Model predictions were madeusing PHREECQC (Parkhurst and Appelo, 1999) and a sorption database for ferric oxide (Dzombak and Morel, 1990).

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Figure 12.—A one-box model depicting the processes considered in modeling dissolved Zn concentrations in Lake Coeurd’Alene.

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Figure 13.—Discharge data and dissolved Zn concentrations for rivers entering and leaving Lake Coeur d’Alene during wateryears (WY) 1999-2001. Concentrations of dissolved Zn in the St. Joe and St. Maries Rivers are not shown and typically were belowpublished detection limits of <1 or <20 mg/L (note: detection limits varied over time); when detected, concentrations in these riverswere <4 mg/L.

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/L

/L

/L

/L

/L

/L

PS

k

Figure 14.—Results of box model calculations for dissolved Zn in Lake Coeur d’Alene. A, Comparisons of measured and modeled dissolvedZn concentrations as a function of water years (WY) 1999 through 2001, taking into account variable discharge and dissolved Zn concentra-tions in the inflow and outflow and benthic fluxes. Concentrations of dissolved Zn as a function of time in the St. Joe and St. Maries Riverswere assumed to be constant at a value of 1.5 mg/L for the model runs. B, Relative contributions of dissolved Zn to the lake from inflowingrivers and from benthic flux. C, Model values for the scavenging rate coefficient (kscav) that fit observed dissolved Zn concentrations inthe outflow.

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Figure 15.—Concentrations of Pb in the blood of people living within the Bunker Hill Superfund site as a functionof time. Data from U.S. Environmental Protection (EPA) web page (www.epa.gov), search on Bunker HillSuperfund. The U.S. Environmental Protection Agency (EPA) and Centers for Disease Control and Prevention(CDC) determined that concentrations of Pb in blood at or above 10 mg/dL present risks to the health of children.

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Water type Number

Range Median Range Medianof samples

pH Dissolved Zn (mg/L)

Ground waters 246. 3.5-7.6 5.61 0.18-759 38.

Tailings seeps 26. 3.8-8.2 5.93 0.09-498 66.

Porewaters 30. 6.2-7.1 6.57 0.005-70 10.

Adits:Kellogg Tunnel 1. 2.7 615All other adits 61. 5.5-8.3 7.34 0.001-58 5.8

CdA River 117. 4.4-9.1 7.05 0.05-21 3.4

Table 1.—Range and median values of pH and dissolved Zn concentrations in waters in the Coeur d’Alene (CdA) River Basin.

[Data sources: Mink and others, 1971; U.S. Geological Survey, 1973; McCulley Frick and Gillman, 1994; Balistrieri and others, 1998; Golder Associates, 1998; Terragraphics Environmental Engineering, 1998; S.E. Box, unpublished data, 1999; Balistrieri and others, 2000; McCulley Frick and Gilman, 2000.]

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Table 2.—Summary of mineralogical and leach studies of particles in the Coeur d’Alene mining district.

Location Smelterville Flats Smelterville Flats Osburn Flats Osburn Flats Upper Woodland Park Upper Woodland ParkEnvironment floodplain channel floodplain channel floodplain channelSample number 201 202 203 204 205 206Total Pb (ppm) 18,500. 5,760. 34,600. 4,665. 123,800. 5,670.Total Fe (%) 16. 5.3 17. 7.9 14. 7.3Total Mn (ppm) 11,720. 3,765. 17,530. 5,160. 2,485. 3,275.

SEM/EDS and XRD1

Bulk - metallic mineralsMajor dispersed Pb, Mn-Pb ox Pb-Mn ox Cer, Pyr Ang Pb-Fe ox, dispersed PbMinor Mn-Pb ox, Pb-Mn-Fe ox Zn-Pb-Fe ox Pb-Fe ox, Mn-Pb ox Fe-Pb ox, dispersed PbTrace Sph, Cer, Pyr Sid, Cer, Sph Sid, Pyr, Sph, Cer Sid, Cer, Sph Sph Sid, Cer, Sph, Ang

Sequential extraction2

% Pb in MgCl2 leach 4.6 13. 5.5 3.3 39. 9.8

% Pb in NaOH leach 1.7 13. 1.6 11. 17. 16.% Pb in EDTA leach 18. 35. 16. 35. 32. 35.% Pb in HNO3 leach 78. 38. 75. 50. 10. 40.

Gastric leach3

% Pb 44. 73. 39. 61. 16. 76.% Fe .7 4.7 .7 2.3 .8 3.5% Mn 4.5 26. 5.5 17. 1.2 30.

1Mineral abbreviations: ox = oxide, Sph = sphalerite (ZnS), Cer = cerrusite (PbCO3), Pyr = pyrite (FeS2), Sid = siderite (FeCO3), Ang = anglesite (PbSO4) 2Sequential extraction leaches (Gasser and others, 1996) 1 M MgCl2: easily soluble minerals such as Pb sulfate (Ang) 0.5 M NaOH: organically complexed Pb and Pb carbonates (Cer) 0.05 M Na2EDTA: specifically adsorbed Pb, Pb oxides, Pb phosphates, and some amorphous Fe/Mn oxides 4 M HNO3: Pb sulfide (galena) and remainder of Fe/Mn oxides 3Gastric leach: 0.1M HCl/0.1M NaCl for 1 hr at 37°C (Gasser and others, 1996)