Guidelines For Metal Leaching and Acid Rock Drainage at Minesites in British Columbia.docx

Guidelines For Metal Leaching and Acid Rock Drainage at Minesites in British Columbia.docx

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GuidelinesForMetalLeachingandAcidRockDrainageatMinesitesinBritishColumbia

GuidelinesForMetalLeachingandAcidRockDrainageatMinesitesinBritishColumbia

WilliamA.PriceandJohnC.Errington

MinistryofEnergyandMines

August1998

TABLEOFCONTENTS

ACKNOWLEDGMENTS

1.INTRODUCTION

1.1PurposeofGuidelines

1.2MetalLeachingandAcidRockDrainage

1.3DevelopmentofGuidelines

2.GUIDINGPRINCIPLES

3.PREDICTION

3.1PredictionPrinciples

3.2PhasedApproach

3.3AvoidingErrors

3.4PredictionManual

3.5Step1-IdentifyandCharacterizeGeologicalMaterials

3.6Step2-PredicttheMetalLeachingandARDPotential

3.6.1TestProcedures

3.7Step3-DevelopMitigationandMonitoringPrograms

4.MEASURESTOPREVENTORREDUCEMETALLEACHINGANDARD

4.1MitigationPrinciples

4.2PreventionandReductionofML/ARD

4.3AvailableMitigationStrategies

4.4EffectivenessofDifferentMitigationStrategies

4.5SelectionoftheBestMitigationStrategy

4.6ContingencyPlanning

4.7InformationRequirements

5.UNDERWATERSTORAGE

5.1GeneralConsiderations

5.2InformationandDesignRequirements

5.3ConstructedSurfaceImpoundments

5.4FloodedPitsandUndergroundWorkings

5.5UndergroundBulkheads

5.6NaturalWaterBodies

6.BLENDINGOFPAGANDNPAGWASTES

6.1GeneralConsiderations

6.2NeutralizationMechanisms

6.3ProblemsWithDemonstratingEffectiveness

6.4InformationandDesignRequirements

7.COVERS

7.1GeneralConsiderations

7.2InformationandDesignRequirements

8.DRAINAGECOLLECTIONANDTREATMENT

8.1GeneralConsiderations

8.2InformationandDesignRequirements

8.3Long-termActiveChemicalTreatment

8.4CommercialAcidLeaching

8.5PassiveDrainageTreatment

9.MITIGATIONOFSPECIFICMINECOMPONENTS

9.1ModificationstoTailings

9.2ModificationstoOpenPitsandUndergroundWorkings

9.3ConstructionMaterials

10.GEOTECHNICALANDHYDROLOGICALCONSIDERATIONS

10.1GeneralRequirements

10.2DrainageManagement

10.3GeotechnicalRequirements

10.4DischargeandReceivingEnvironmentObjectives

11.BRITISHCOLUMBIAMINEREGULATION

11.1PermittingandMineApproval

11.2FinancialSecurity

11.3OperationalMonitoring

11.4AnnualReclamationReports

11.5ML/ARDPredictionandPreventionPlans

11.6HistoricMinesiteswithMetalLeachingandARDConcerns

11.7Exploration

12.COMMITMENTTOIMPROVEDPRACTICESANDREGULATION

12.1Research

REFERENCES

FOOTNOTES

Acknowledgments

TheseguidelineshavebeencreatedwithassistancefrommembersoftheMinistryofEnergyandMines’MetalLeaching/AcidRockDrainageExpertAdvisoryCommittee:

∙GarryAlexander--MinistryofEnvironment,LandsandParks

∙StephenDay--Norecol,DamesandMoore

∙KeithFerguson--PlacerDomeNorthAmericaLtd.

∙GlendaFerris--NorthernEcologyActionCommittee

∙WalterKuit--ComincoLtd.

∙KevinMorin--MinesiteDrainageAssessmentGroup

∙AlanYoung--EnvironmentalMiningCouncil

Attherequestoftheauthorsdetailedreviewswerealsocarriedoutby:

∙PeriMehling--MehlingEnvironmentalManagement

∙GillesTremblay--MENDSecratariat

Theauthorsgratefullyacknowledgetheextensivetechnicalcontributionsandthetimedevotedtothisprojectbytheaboveindividuals.However,theirsupportshouldnotbeconstruedasanendorsement,inwholeorinpart,bythemorbytheorganizationstheyrepresent.

KimBellefontaine,MinistryofEnergyandMines,isthankedfortheextensiveimprovementsshemadetotheclarityandtogeologicalaspectsofthedocument.TimEaton,MinistryofEnergyandMines,checkedgeotechnicalaspectsofthereport.BobHartandJimHofwebberprovidedmuchofthedetailregardingdischargeandreceivingenvironmentobjectivesandtherequirementsoftheMinistryofEnvironment,LandsandParks.ValuablecontributionswerealsomadebyGrace Harris,Carol HowellandSylviaVanZalingenoftheMinistryofEnergyandMines;Laura DuncanoftheEnvironmentalMiningCouncil;andvariousregionalreviewersoftheMinistryofEnvironment,LandsandParks.

TheMinistryofEnergyandMinesiscommittedtoimprovingexistingpracticesandregulation.Commentsonthisdocumentandotheraspectsofmetalleachingandacidrockdrainageregulationshouldbesubmittedto:

WilliamPrice

MinesBranch

MinistryofEnergyandMines

Bag5000

Smithers,BC V0J2N0

ReturntoTableofContents

1.Introduction

1.1PurposeofGuidelines

Therearenumerousexamplesthroughouttheworldwhereelevatedconcentrationsofmetalsinminedrainagehaveadverseeffectsonaquaticresourcesandpreventthereclamationofminedland.Metalleaching（ML）problemscanoccurovertheentirerangeofpHconditions,butaremostcommonlyassociatedwithacidrockdrainage（ARD）.Onceinitiated,metalleachingmaypersistforhundredsofyears（ArnesenandIversen,1997）.InNorthAmerica,MLandARD（ML/ARD）haveledtosignificantecologicaldamage,contaminatedrivers,lossofaquaticlifeandmultimillion-dollarcleanupcostsforindustryandgovernment.TheARDliabilityassociatedwithexistingCanadiantailingsandwasterockisestimatedtobebetween$2 billionand$5 billion（FeasbyandTremblay,1995）.

PreventingimpactsfromML/ARDisthemostcostlyandtimeconsumingenvironmentalissuefacingtheBritish Columbiaminingindustry.Itisalsooneofthemosttechnicallychallenging.Duetopoorhistoricalpractices,largeremediationcosts,technicaluncertaintyandthepotentialfornegativeenvironmentalimpacts,ML/ARDisamajorissueofpublicandregulatoryconcern.

UnderexistingBritish Columbialegislationandpolicies,miningcompaniesarefullyresponsibleforenvironmentalprotectionandreclamationattheirminesitesandmustdemonstratetheeffectivenessoftheirplansinthedevelopment,operationandclosurephasesofthemine（BCMEMandBCMELP,1998）.Theresponsibilityofregulatoryagenciesistoindicate,asclearlyaspossible,whatconstitutesacceptableminedesignandadequatetechnicalevidence.

Althougheveryrock,wasteandminesiteissomewhatunique,thereareML/ARDinformationneeds,testprocedures,designobjectivesandmanagementrequirementsthatapplyundermostcircumstances.Theprimaryobjectivesofthisdocumentandthecomplementarypredictionmanual（Price,1997）aretodescribegenericrequirementsandoutlinecommonerrors,omissionsandconstraints.Thisinformationwillassistminesindevelopingcomprehensiveproposalsthatincludethenecessarydocumentationandconsiderationofriskforsoundenvironmentalmanagement.

TheguidelineshavealsobeenproducedtoassistregulatorsandmembersofthepublicwhoareinterestedinreviewingML/ARDwork.TheMinistryofEnergyandMines（MEM）endeavorstobetransparentinitsregulationandtocarryoutcomprehensive,wellinformedminereviews.Bydocumentingthetechnicalbasisforpresentpractices,MEMhopestopromotegreaterunderstandingofML/ARDissuesandtoenabletheidentificationofgapsintheknowledgebase.

TheguidelinesprovidegeneraldirectiononML/ARDissuesandmanagementwithoutlimitingoptionsandapproaches.Theyweredevelopedfrompreviousexperience,primarilyinBritish Columbia,anddonotapplytoallminesitesandconditions.Usersoftheguidelines,bothinthisProvinceandinotherbiogeoclimaticregimesorregulatoryjurisdictions,mustconsidersite-specificconditionsandmaterialswhendecidingwhichprinciplesandproceduresapply,andhowtheyshouldbeimplemented.

1.2MetalLeachingandAcidRockDrainage

Metal1leachingandacidgenerationarenaturallyoccurringprocesseswhichmayhavenegativeimpactsonthereceivingenvironment.TheenvironmentalimpactofML/ARDwilldependontheirmagnitude,thesensitivityofthereceivingenvironmentandthedegreeofneutralization,dilutionand/orattenuation.Factorswhichenhancemetalleachingincluderapidlyweatheringmetal-containingminerals,drainageconditionsthatincreasesolubilityandhighflowratesthroughcontaminatedmaterials.

Acidgenerationoccurswhenmineralscontainingsulphideandelementalsulphurareexposedtotheweatheringeffectsofoxygenandwater.Acidityisgeneratedfromtheoxidationofsulphurandtheprecipitationofferriciron.ARDoccurswhentheresultingacidityisentrainedbywater.AlthoughARDhasreceivedmostoftheattention,theprimarysourceoftoxicityaremetals.Elevatedmetalleachingisassociatedwithacidicdrainageduetohighmetalsolubilityandsulphideweatheringratesunderacidicconditions.Formanyrocktypes/environmentalconditions,metalleachingwillonlybesignificantifdrainagepHdropsbelow5.5or6.

However,neutralpHdrainagedoesnotnecessarilypreventmetalleachingfromoccurringinsufficientquantitiestocausenegativeimpacts.Whilethesolubilityofaluminum,ironandcopperisgreatlyreducedinneutralpHdrainage,elementssuchasantimony,arsenic,cadmium,molybdenum,seleniumandzincremainrelativelysolubleandcanoccurinsignificantlyhighconcentrations.UnlikeARD,neutralpHmetalleachingisgenerallyonlyaconcernifdischargeisintoasensitiveresourceand/orwithlittledilution.HighconcentrationsofmetalsinneutralpHdrainageoftenresultfromlocalizedrelativelysmallzonesofacidicweathering.

ThecharacteristiclowpHvaluesandrust-colouredironstainingassociatedwithARDareoftenfoundinnaturalwatercoursesinthevicinityofundisturbed,naturallyweatheredoutcropsofsulphide-bearingrock（i.e.,gossans）.TheProvincialRegionalGeochemicalSurvey,whichhassampledandanalyzedstreamsthroughoutBritish Columbia,hasfoundnumerousoccurrencesofnaturalacidicdrainage（Lettetal.,1996）.Rapidsulphideoxidationinundisturbedareas