Draft environmental assessment for Montana Tunnels Mining, Inc., operating permit no. 00113 : tailings impoundment expansion

54 Pages·1994·1.2 MB·English

by  Montana. Department of State Lands

DEPARTMENTOFSTATELANDS
MARCRACICOT,GOVERNOR ' 162SELEVENTHAVENUE
^—STATE OF MONTANA
[phone] HELENA,MONTPA.NO.AB5O9X62200-11660011
STATEDOCUMENTSCOLLECT!C.
November23,1994 MAR 3 1395
MONTANASTATELIBRARY
HELEN1A51,5MEO.N6TtAhNAAVE5.9620
DearReader:
EnclosedforyourreviewisaDraftEnvironmentalAssessment(EA)preparedbythe
DepartmentofStateLands(DSL)andtheBureauofLandManagement(BLM). TheEA
evaluatesaproposalbyMontanaTunnelsMining,Inc.toraisethetailingsimpoundment
embankmentfromthepresentlypermittedelevationof5515feettotheelevationof5600feet.
PubliccommentonthisEAwillbereceivedbytheagenciesuntil5:00p.m.December
16,1994. CommentsshouldbeaboutadequacyoftheEAinassessingissues,newinformation
notconsideredthatmayinfluencetheanalyses,andclarification. Commentsshouldbespecific.
Theagencieswillusethesecommentsandagencyresponses,theEA,andtheapplicationtomake
afinaldecisiononthepermit. Thedecisionmaybetoapprove,approvewithmodifications,or
denytheproposal.
CommentswillbeacceptedbycallingBobWinegarat444-2074orbywritingto:
BobWinegar
MontanaDepartmentofStateLands
POBox201601
Helena,MT 59620-1601
Thankyouforyourtimeandconsideration. PleasecallDSLifyouhaveanyquestions.
Sincerely,
RobertC.Winegar
ProgramManager
HardRockBureau
ReclamationDivision
SM/rhv " ' • 1! .
"ANEQUALOPPORTUNITYEMPLOYER"

DraftEnvironmentalAssessment
for
MontanaTunnelsMining,Inc.
OperatingPermitNo.00113
TailingsImpoundmentExpansion
Preparedby
MontanaDepartmentofStateLands
and
U.S.DepartmentoftheInterior
BureauofLandManagement
November23, 1994
i
TABLEOFCONTENTS
CHAPTBAE..RPPI:URROPPPOUOSRSEPEODASNAEDCATNNIEDOENNDEEDFORACTION 111
BackgroundandProjectLocation 1
TailingsImpoundmentConstructionSummary 2
C. SCOPINGPROCESS 7
IssuesIdentifiedandEliminatedfromFurtherConsideration 7
SignificantIssues 7
D. REASONABLYFORESEEABLEACTIVITIES 8
E. AGENCYROLESANDRESPONSIBILITIES 8
MontanaDepartmentofStateLands(DSL) 8
BureauofLandManagement(BLM) 8
StateHistoricPreservationOffice(SHPO) 9
MontanaDepartmentofHealthandEnvironmentalSciences 9
AirQualityBureau(AQB) 9
WaterQualityBureau(WQB) 9
DepartmentofNaturalResourcesandConservation(DNRC) 9
HardRockMiningImpactBoard 10
CHAPTERII: SUMMARYOFPROPOSALSANDALTERNATIVES 11
A. COMPANYPROPOSEDALTERNATIVE 11
EmbankmentConstructionMethods 11
FinalReclamation H
B. AGENCYMODIFIEDALTERNATIVE 12
EmbankmentConstructionMethods 12
FinalReclamation 12
C. NOACTIONALTERNATIVE 12
CHAPTERIII: AFFECTEDENVIRONMENT 14
A. SEISMICITY 14
BC.. HSOYIDLROLOGY ..... U14
DE.. WVIELGDELTIAFTEION ' 1154
GF.. AWQEUTALTAINCDSS ' ' 1155
CHAPTERIV: ENVIRONMENTALCONSEQUENCES 16
A. EFFECTSOFCOMPANYPROPOSEDALTERNATIVE 16
DisturbedAcreage 16
Reclamation 16
Hydrology 18
Soil 18
Vegetation 18
Wildlife [ ' ' ' ' is
Aquatics 19
Wetlands 19

B. EFFECTSOFAGENCYMODIFIEDALTERNATIVE 19
C. EFFECTSOFNOACTIONALTERNATIVE 20
D. UNAVOIDABLEADVERSEEFFECTS 20
E. SHORT-TERMUSESANDLONG-TERMPRODUCTIVITY 20
F. IRREVERSIBLEANDIRRETRIEVABLECOMMITMENTSOF
RESOURCES 20
G. CUMULATIVEIMPACTS 20
SUMMARY
21
LISTOFPREPARERS 22

I: PURPOSEANDNEEDFORACTION
A. PROPOSEDACTION
OnJanuary27,1994,theMontanaDepartmentofStateLands(DSL)receivedan
applicationtoamendoperatingpermit#00113fromMontanaTunnelsMining,Inc.(MTMI), a
whollyownedsubsidiaryofPegasusGold,Corp. Theamendmenttothepermitisforexpansion
ofthecurrenttailingsimpoundmentfacilityusingthemodifiedupstreamconstructionmethod.
Theexpansionwillraisetheembankmentfromthecurrentlypermittedelevationof5515feet
MSLtotheproposedelevationof5600feetMSL.
Theexpansionwouldincreasethecapacityofthefacilityfrom49milliontonsto67
milliontonsandentailanincreaseindisturbanceof73acres(6.2acresinthetailingsdam,66.8
acresforthetailingspond). Iftheexpansionisallowed,thetotalareacoveredbythe
embankmentraiseandexpandedpondwouldincreasefrom181acresto254acres.
Theanalysesinthisdocumentsupplementspreviousanalysesandwillbeusedinagency
decisionmaking. TheDSLandtheBureauofLandManagement(BLM)mustreviewand
evaluatetheproposalanddeterminewhethertoapprove,approvewithmodifications,ordenythe
proposal.
B. PURPOSEANDNEED
MTMIrecoversgold,silver,lead,andzincfromtheMontanaTunnelsmine. These
mineralsareusedprimarilyforindustrialpurposes. MTMIhasidentifiedanadditional18
milliontonsofminableorereserves. Thepurposeandneedoftheimpoundmentexpansionisto
increasethecapacityofthetailingsfacilitytoallowforthestorageoftailingsfromtheprocessing
ofexistingandnewreserves. Thenewreserveswouldexpandtheminelifeapproximately4
yearsfrom1997totheyear2001.
BackgroundandProjectLocation
MontanaTunnelsislocatedapproximately 10airmilesduenorthofBoulder,MT,and15
aiinrTm7iNl,esRs4ouWt,hJoeffHfeerlseonna,CoMuTn.ty,TMheTpe(Frimgiutrebo1u)n.daFriyguirnecl2uddeespipcatrststhoefmSiecnteiosniste8a,nd9,th1e6,and17
surroundingareaaswellasperennialandephemeralstreams. Figure3depictsthegeneral
facilitylayoutatMTMI.
TheMontanaTunnelspermithistoryissummarizedasfollows:
Date Action
00113 2/20/86 1500acresformineandfacilities
Amd001 nodate plantsiterelocation
Amd002 5/1/86 decreaseinproduction/permitareareducedto1497
acres
1