DWQ-2024-000291

STATEMENT OF BASIS
Barrick Mercur Mine Reclamation Project
Closure Phase Period Renewal
Ground Water Quality Discharge Permit No. UGW450002
January 5, 2024
Basis For Permit Renewal
BarrickResources (USA), Inc.operatedgoldminingandprocessingfacilitiesatMercurfrom1982through1998. DuringthisperiodgroundwaterqualitydischargepermitUGW450001wasobtainedfor Valley Fill
Leach Area 3 (VFL3) and UGW450002 was obtained for the Reservation Canyon TailingsImpoundment.Alsoduringthatperiod,theDivisionissuedStipulationandConsentOrder Docket No. GW90-03-A to
resolve operational issues associated with Valley Fill Leach Area 2 (VFL2). Effective April 1998, the mine entered full closure status.
UGW450001expiredinDecember1999.TheConsentOrderforVFL2remainedineffectduring themodeldemonstrationperiodthrough2001. UGW450002 will expire in April 2018. In light of the closurestatusofthemineandtheinter-relationshipsofthefacilitiesdiscussedabove,consolidating
the Consent Order stipulations and both groundwater permits into a single enforceable regulatory toolin2000wasdeemedappropriate.ThisapproachincorporatedintoUGW450002theapplicable termsandconditionsofUGW450001.Thepermitalsoreferencedthetermsandconditionsofthe
ConsentOrderforVFL2.UGW450001terminatedwiththeeffectivedateofpermitmodificationto UGW450002 in 2000.
ThePermitteemaintainedarecordofcompliancewiththeconditionsofpermitUGW450001, includingtheVFL2ConsentOrder,throughthepreviouspermitterm priortoincorporationinto UGW450002inAugust2000.ThePermitteehasalsomaintainedarecordofcompliancewiththe
conditionsofUGW450002bothpriorandsubsequenttotheincorporationofUGW450001andthe VFL2 Consent Order into UGW450002 in August 2000. No adverse effects to ground water, the environmentorpublichealthareknowntohave
occurredduetotheoperationofVFL3,VFL2,or thetailingimpoundmentduringthisperiod. BarrickwillcontinuetotransferneutralizedVFL3 draindownwaterandtailingsimpoundmentincidental seepage to
the East Bay (a lined facility integraltotheReservationCanyonTailingsImpoundment)throughtheendoftheclosureperiodas neededuntilsuchtimethattreatmentoftheeastbaywaterhasmettheapprovedgoalsandobjectives
fordischargetoanonsitelocationunderPermitUGW450002.Barrickhascompletedthecessation ofoperationsandreclamationofVFL3associatedwiththispermitaswellasthecompleteclosureof VFL2.PermitUGW450001isincorporatedintoUGW450002onthebasisthat:1)allgroundwater
protectionlevelswillcontinuetobemet;2)thesampling,monitoringandreporting proceduresaredeemedadequatetodeterminecompliancewiththeapplicablerequirements;3)there isnoexpectedimpairmentofpresentorfuturebeneficialusesofgroundwater;and4)finalclosure
of VFL3 will be completed under the provisions of UGW450002.I.DESCRIPTION OF FACILITIES
ValleyFillLeachArea3Description -BarrickMercurMineoperated(VFL3)forthe extraction of gold using cyanide solutions fromJanuary, 1991 through 1997. The facility is nowreclaimedandawaitingfinal,permanentclosure.
The facility is located in the SW1/4, SW1/4,Sec32,T.5S,R3WandtheNW1/4,Sec5,T.6S.,R.3W inMercurCanyoninthe southernOquirrhMountainrangeofTooeleCounty. The facility is limited to one cell
approximately1,700feetlongand750feetwide.Attheendofthefacility'slifeitcontained approximately5milliontonsofspentheapleachorewithanaveragedepthof150feet.The heapwasneutralizedduring1997andcoveredduring1998.
In1997,averticalsolution dewateringwellwasputinplacetopumpinconcertwiththepumpingcisterntheremaining fluidsfrom thisleachareaandtransportviapumpingandpipingtotheEastBaylinedcell withintheReservationCanyonTailingImpoundment.AfterthefreedrainingfluidsinVFL3
achieve model-predicted flow rates, the wells will be removed and final closure will be complete. Residualwatershavebeenmodeled de minimis as to probable impact to ground water at the
property boundary.
ReservationCanyonTailingImpoundmentFacilityDescription -Barrickoperatedatailingimpoundmentat the MercurMine forthedisposaloftailings fromthebeneficiationand processingofgoldfrom itsgoldmillingoperation.
Thetailingimpoundmentislocatedin ReservationCanyoninthesouthernOquirrh MountainrangeontheTooele/UtahCounty lineinSection5ofTownship6SouthandRange3West Salt Lake Base and Meridian.Thetailingfacilityconsistsofasaddle
dam,maindam,upstreamlevee,internalEastBaylinedcell,approximately27milliontonsof depositedmilltailing,andalldrainsandexternalcontainmentpondsassociatedwiththemain damandsaddledam.Thetailingtreatmentsystemisnolongerinuseasthemillingoperations
have been dismantled and removed.
ValleyFillLeachAreaNo.2Description -BarrickMercurMineoperatedVFL2forthe extractionofgoldusingcyanidesolutions. The facility was closed in July 1993, was neutralizedinSeptember1994,andcoveredbyNovember1995.Thefacilityremainssubject
to the conditions of Stipulation and Consent Order now contained in Permit UGW450002. Those conditions remaining are ground water monitoring and dewatering of the leach pad. ThefacilityislocatedintheNE1/4,Sec8,T.6S,R3WandtheSE1/4,Sec5,T.6S.,R.3Win
thesaddlebetweenManningandMercurCanyoninthesouthernOquirrhMountainrangeof TooeleCounty.Thefacilityislimitedtoonecellapproximately1200feetlongand500feet wide.Final cover placement on
VFL2 was completedinSeptember1995.During1998,aninfiltrationmanholewasinstalledthroughthecovertoaccommodate the infiltration of incidental area flows and seepage in Manning Canyon. Barrickintendstogrouttheleakagecollectionpipeclosed,and
reclaim theleakagecollectionsystem area. Barrickcompletedthe5-yearpost-closure monitoringoftheleakagecollectionsysteminApril2001anddemonstratedthatpost-closure monitoringresultsmetpreviousmodeledpredictionsforthesystemanddrilledouttheVF2
liner.Residualwatershavebeenmodeleddeminimisastoprobableimpacttogroundwaterat the property boundary.II.GROUND WATER
Class-Basedonthetotaldissolvedsolidsdatafrom elevenmonitoringwellsatthesitethe groundwaterisdefinedasbothClassIAandClass II. The average dissolved solids values fromthe wells range from345
mg/l to 2,124 mg/l.
Background-Whengreaterthan50%ofthebackgroundsamplesforaparticularconstituent weredetectable,backgroundwasdeterminedbyestimatingthemeanandstandarddeviationof all background samples.
Protection Levels- Class IA is pristine ground water. ClassIIgroundwaterisprotectedfor useasdrinkingwaterorothersimilarbeneficialusebytheGroundWaterQualityProtection Regulations,UACR317-6.ProtectionLevelsaredeterminedbasedonthecriteriaofUAC
R317-6.4 taking into account naturally occurring degradation in accordance with UACR317-6-6.10.
GroundWaterMonitoring -ThePermitteehasinstalledelevenmonitoringwellsatthesite. Drywellsarenotusedascompliancemonitoringpointsunderthispermit.WellsMW-1,MW-
2,MW-9,MW-10,MW-11,MW-13,MW-15,MW-16,MW-17,MW-18,andMW-19willbe used as compliance monitoring wells. These wells will be monitored for metals, inorganic ions,pH,cyanide,nitrate,nitrite,ammoniaandtotaldissolvedsolids.Routinemonitoringwill
be on a semiannual basis. Reporting will be on a semiannual basis.
III. CLOSURE AND RECLAMATION
Permanentclosureandfinalreclamationof theVFL3andtheReservationCanyontailing impoundmentwasinitiatedin1998aspartofamine-wideclosure.Underpreviousversionsof these permits, permanent closure
and final reclamation requirements that are protective of groundwaterwereincorporated. Theseinclude the following activities that have been implemented.
TAILINGS IMPOUNDMENT-Placementofperforateddrainagepipeswithadraingravelcoverintheconcretedrainage aprons,encapsulatingthegraveldrainswith filterfabric,andcoveringof drainswith subsoil
and top soil.-Coveringandre-vegetativeseedingofthedownstreamembankmentsoftheMainButtress andLeveeButtresswithaminimumone-footthicklayerofsubsoilandaminimumone- foot thick layer of topsoil.
- Coveringandre-vegetativeseedingoftheareabetweentheLeveeButtressandthe Saddle Dam-DesignandconstructionofastormwaterdiversionchannelthroughtheSaddleDamto permitfreedrainageofstormwaterthatfallsbetweentheLeveeButtressandtheSaddle
Dam.-Re-gradingcrestheightoftheButtressEmbankmentrockfillontothetailingsbeach leavinganormalsix-foothighinterimrockfillbermabovethetailingssurfaceforstorm water control and freeboard.-Placement
of cover systemover the tailing surface.-Installationofanincidentalareaflowandseepagepipelineconnectiontoaninfiltration manhole in the Valley Fill Leach Area No. 2 facility.-Upgradingexisting,andconstructionofadditionalinterimstormwaterdiversion
channels.
VALLEY FILL LEACH AREA 3-Dismantling and removal ofprocess facilities.-Implementationofpermanentclosureandfinalreclamationbyre-grading,re-contouring, shaping,placementofasoilcoversystem
(minimum 3feetofsubsoilandminimum 1 foot of top soil) and re-vegetative seeding of the Valley Fill Leach Area No. 3 facility.
VALLEY FILL LEACH AREA 2-Dismantling and removal ofprocess facilities.-Completionofcontouring,shaping,placementofasoilcoversystem(minimum3feetof subsoilandminimum 1footoftopsoil)andre-vegetativeseedingof
theValleyFill Leach Area No. 2 facility.