Analysis of suspended sediment, metals, and arsenic released to the Clark Fork River during a pipeline crossing event

50 Pages·2000·1.3 MB·English

by  Suplee, Michael W

MONTANASTATELIBRARY
308640015 66903
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ANALYSISOFSUSPENDEDSEDIMENT,METALS,ANDARSENICRELEASEDTOTHE
CLARKFORKRIVERDURINGAPIPELINECROSSINGEVENT
By
MichaelW.Suplee,Ph.D.
MTDepartmentofEnvironmentalQuality
WaterQualityStandards
July11,2000
STATEDOCUMENTSCOLLECTION
t-tB 122001
MONTANASTATELIBRARY.
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1 Abstract
OnApril1,2000,YellowstonePipelineCompanyreplacedasectionofgaspipeline
whereitcrossesundertheClarkForkRivernearTurah,MT. Duetoheavymetalscontamination
oftheriversedimentsfromhistoricminingandsmeltingintheheadwaters,theDepartmentof
EnvironmentalQualitydesignedasamplingplantomonitorthewatercolumnduringinstream
construction. Samplesfortotalsuspendedsediments(TSS),hardness,andtotalrecoverableCu,
Pb,ZnandAswerecollected305mand1.68kmbelowthework,and366mupstreamofthe
work. Integratedtransectsampleswerecollectedintriplicateateachsiteusingahand-held
depthintegratingsampler. Sampleswerecollectedatall3sitesthedaypriortowork,andthen
during3distinctworkphases;trenching,pullingofthepipeacrossthechannel,andburial.
Sampleswerealsocollected4daysafterworkbeganwhennoinstreamconstructionwas
occurring. Duringtrenching,thematerialliberatedtotheriverwasveryfine,asTSS
concentrations1.68kmbelowtheworkwereequivalentto305mbelow. Furthermore,theMT
acuteaquaticlifestandardwasslightlyexceededbyCu. Aftertrenchingandduringpipepulling,
TSSconcentrationsdroppedrapidlytobackground. Pipeburialcommencedusingtheexcavated
material,andwascompletedusingaborrowmaterial(soil). Theborrowmaterialcausedalarge
increaseinTSSandraisedtheCuconcentrationto57.3ug/L,aconcentrationsimilartowhatis
foundatthissiteduringrunoffandfurther,exceededtheacuteaquaticlifestandardby2.5times.
Theborrowmaterialwasmuchcoarserthanthatoftheriverbottom,andmostlysettledout
beforereachingthelowestsite. Bythe4thdayafterworkbegan,allinstreamconcentrationshad
/ returnedtopre-workvalues. Loadcalculationsbasedonconcurrentflowdayindicatedatotalof
113.4metrictonsofsuspendedsedimentwerereleasedtotheriverfromtheentireproject. This
valueisanorderofmagnitudelowerthantypicaldailyTSSloadsduringClarkForkhigh-flow
events,but5timeshigherthanbackgroundTSSduringtheconstruction. Amongthevarious
workprocedures,burialcontributedapproximately90%oftheTSSload,followedinimportance
bytrenchingandpipepulling.
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Introduction
OnApril1,2000,YellowstonePipeLineCompanyreplacedasectionofgaspipeline
whereitcrossedundertheClarkForkRivernearTurah,Montana. Replacementwasnecessary
duetocontinualdowncuttingoftheriveratthelocation,whichthreatenedtoexposetheexisting
pipe. Replacementinvolveddigginga3.1m-deeptrenchintotheriverbed,dragginganew
sectionofpipeacross,andreburyingit. Water-columnmetalsconcentrationsatthissite
frequentlyexceedstatewaterqualitystandards,particularlycopper(Cu;USGS1997).Metals
contaminationisalegacyof19thand20thcenturyminingnearButte,MT,whereminetailing
washistoricallydumpedintotheClarkForkRiverheadwaters. Thesetailingshave,overtime,
moveddownstreamandhavebeendistributedinthebedsedimentsandfloodplainoftheriver
(AxtmannandLuoma1991). Concernsraisedoverthepotentialreleaseofwater-bornemetals
duringthetrenchingoftheriverbedledtheDepartmentofEnvironmentalQualitytoconduct
samplingduringtheinstreamconstructionprocess. Cu,lead(Pb),zinc(Zn),andarsenic(As)
/• wereselectedasthemostlikelycontaminants. Totalsuspendedsolids(TSS)werealsosampled,
aswashardness,whichwasusedtocalculateaquaticlifestandards(MTDEQ1998). The
primaryobjectiveofthestudywastodeterminetheextentoftheimpact,bothfromaloadingand
concentrationperspective,resultingfromthissingleinstreamconstructionevent.
MethodsandMaterials
Samplingdesign-spatialandtemporallayout. Sampleswerecollectedat3sites(A,B,C). Site
A(upstreamcontrol)waslocated366mupstreamfromthecrossingsite,siteBwaslocated305
mbelowthecrossingsite,andsiteCwaslocated1.68kmdownstreamofthecrossingsite(Fig.
1). SiteCwassampledtodeterminetheextenttowhichsuspendedmaterialmoveddownstream.
Samplingwasundertakenthedaypriortothechannelcuttinginordertodeterminetherelative
similarityofthe3sites.Theplacingofthepipetheninvolvedthreeworkphases. Thefirstphase
wasthecuttingofa3.1m-deeptrenchintotheriverbottomperpendiculartoriverflow(herein
referredtoas"trenching"). Next,thepipewaspulledinitstrenchfromtheleftbanktotheright
viaacable("pipepulling"). Finally,thepipewasreburiedusingtheexcavatedmaterialand
additionalmaterialbroughtfromaborrowarea("burial"). All3sitesweresampledduringeach
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Fig.1. Pipelinecrossingsiteandlocationof
3samplingsitesontheClarkForkRiver,
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\fc^ ofthesemajorworkevents,duringthepeakofworkactivity. Samplesattheupstreamcontrol
werecollectedasnearintimeaspracticaltotheoccurrenceofagivenworkevent. SiteCwas
alwayssampled40-50minaftersiteB,dependinguponflow. Atmeasuredflows40-50minwas
appropriatetoallowagivenparticletotravelfromsiteBtoC. Thefinalsetofsampleswas
collected4daysaftertheworkwasbegun,atwhichtimenoinstreamworkwasoccurring.
Samplecollectionandanalysis. Threereplicateswerecollectedateachsiteduringeach
sampling. Asystematicsamplingapproachwasused,eachreplicatebeingacompositeof20-25
subsamplescollectedatevenintervalsalongatransectacrossthechannel. Sampleswere
collectedusingadepthintegrating,isokinetic-nozzlesampler(modelDH48;Edwardsand
Glysson1999). Thisapproachresultedinasampleofapproximately2litersperreplicate,each
replicatetakingapproximately5mintocollect. Eachsamplewasanalyzedfortotalrecoverable
Cu,Pb,Zn,andAs,aswellashardnessandTSS. Allsamplebottleswereacidwashed/distilled-
waterrinsedpriortouse,whiletheDH48samplerwasacidwashed/distilled-waterrinsedwhen
takenbetweensites,andbetweenworkevents. Afield-equipmentblankwascollectedatsiteC.
Sampleswereicedandheldinthedark(3daysmaximum)untildeliveredtotheMontana
EnvironmentalLaboratory(Helena,MT)foranalysis. Dissolvedoxygen,temperature,
conductivity,andpHwerealsomeasuredatsiteBusingahand-heldmeter. Ca,Mg,CuandZn
wereanalyzedusingEPAmethod200.7. ThereportingvalueforCuwas1ug/L,forZn,5ug/L.
PbandAswereanalyzedviaEPAmethod200.9,eachwithareportingvalueof1ug/L. TSSwas
analyzedusingEPAmethod160.2,withareportingvalueof1mg/L.
Ameanandstandarddeviationwascalculatedforeachanalyte. Althoughsamplingwas
systematicratherthanrandomized,theformulasforestimatingsamplestatisticswereidenticalto
thosethatwouldbeusedforarandomizedsampling. Thisapproachisapplicablewhenthe
sampledpopulationexistsinarandomorder(Cochran1977),whichwasmostlikelythecasein
thisstudy.
Loadapproximations. Metals,AsandTSSloadingtotheClarkForkRiverwascalculatedusing
USGSflow-datafromtheTurahBridgestation,whichwasavailableontheUSGSwebsite. The
TurahgaugestationislocatedbetweensitesAandB. Foreachcalculation,thereplicatemean
foragivenanalytewasusedastheinstreamconcentration. Grossloadduringagivenwork
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