NC0004774_Buck CAP Part I_Appx C_Final_20151120

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ELECTRIC POWER
RESEARCH INSTITUTE&1emorandum
Octobere9,e2015e
TO:cEdeSullivancandeTylereDubosee e
FROM:d3rucecHensele e
SUBJECT:e BUCKdVIODEUREVIEWe
Summary
EPRIdiase; evieweddhed3uckanodelcreportcandcfl lesq)rovidedd)yDukecEnergy,diDRe
Engineering,dnc.,canddhedJniversitywfCNortheCarolinaeCharlotte. eThecreviewavascperformede
byeTamescRumbaugh�EnvironmentalcSimulations,dnc.),exithdnputd)yeChunmiaoeZhengcande
myself d3asedwndhiscreview,dtaiswuroopiniondhat,asubjectdodheacaveatsd)elow,dhisanodele
iseset-upcandeneetsdtseflowe3nddransporta;alibrationwbjectivesesufficientlyttoeneetatsc finale
obj ectivewfapredictingwffectswfocorrectiveaactionaalternative swnegroundwateroquality. eThee
caveatscassociatedawithdhisaDpinioneare: e
• Constantdieadsazseddocrepresentesomecboundariesanayq)rovideeancanmitigatedesourcee
ofowatereforasimulationwfcanyocorrectiveaactionaalternativesdhatcpotentiallyainvolvee
pumpingeieardhosed:)oundaries. odfxorrectivecactionsdnvolveepumping,xonsidercane
alternativedodheoconstantcheadsebelowdayere5 arepresentingdheeYadkineRiver. e
• Boroncandearsenicawerecaddeddoetheanodel&iaeconstantwoncentrationcboundaries.e
Usew fdhisd)oundarywonditionenayanakeeitodifficultdordhec nodeldocsimulatee
cappingca s aacremedialcstrategy. e
Specific Comments
Model Report, Setup, and Calibration
a) Is the objective/purpose oj'modeling clearly defined?
Yes.eTheo)bj ectivecandcpurposea)fdhecmodelingeisoclearlyadefinedaincSectionel .2aase
consistingoDfdhreeemaineactivities: o�developmentoufcaocalibratedcsteady-stateeflowanodelwfe
currentoconditions,odevelopmentdofcaahistoricaldransientanodeleDfw,onstituentdransporte
calibrateddowurrentoconditions, candq)redictiveesimulationsaDfadifferentacorrectiveeactione
options.e
b) Is the site description adequate?
Yes.oSectionel .1 e)fdheareportq)rovidescaodescriptiona)fdheasitedhateiscadequateefore
evaluatingetheenodelaforcbothdloweanddransportq)urpo ses. e
c) Is the conceptual model well described with appropriate assumptions?
Yes.xThe(vonceptualc nodelesectionaeontains(subsectionsodiscussingdhecaquiferasysteme
framework,dheegroundwaterdlowcsystem, diydrologicd)oundaries,diydraulicd:)oundaries,e
sourcescandasinks,evatercbudget,anodeledeconstituentswfdnterest,candoconstituentdransport. w
TheeCSAareportdsareferencedanodescribingeaquiferq)roperties. c-,Theernethodaxseddoo-,stimatee

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rechargeeisodiscussedealongavithereferences. wTheerationaled)ehinddhewhoicewfu�onstituentse
toebeemodeleddsadiscussed.e
d) Is the numerical model properly set up (steady state or transient; initial condition;
boundary conditions; parameterization; etc)?
i) Appropriateness of the simulatore
Thecaseo)fcN40DFLOW-NWTaandcT\4T3DMSdoesimulateegroundwatereflowcandacontaminante
transport,erespectively,eared)otheappropriateefordheemodelingwbj ectiveseandcrepresenteane
industryestandardeincehoiceaDfcs emulators. e
ii) Discretization: temporal and spatial (x y notably z)
Thecspatialadiscretizationefordhisanodelascaeconstante20cft, avhicheisemoredhancadequatedoe
delineateadifferencesdnesimulatedcheadseandwoncentrationseforeallcreasonable(valibrationcande
predictivecpurposes. e
Fordransportesimulations,dhecCouranteNumberc ndctheeGridcPecletcNumberacancbewseddoe
determineavhetherodiscretizationascnumericallyeappropriatecforcaegivenanodel.cdndhisanodel,e
transportdimeestepsearec utomaticallywalculatedd)ydheesimulatorebasedauneacspecifiede
CouranteNumber(constrainto)fel.oeThiso-,nsuresdhatdemporalodiscretizationasc ppropriateefore
theesp atialediscretizationmfdheemodel. e
TheeGridePecletcNumber4Pe_gride=ell/a)ovancbecaseddoxvaluateavhethermumericale
dispersionodominatesoconstituentdransportd)asedoonespatialodiscretizationeandcphysicale
dispersion. oiGridePecletenumberscpreferablydessdhane2candeaoanoredhanel Oeareegenerallye
recommendeddoeminimizemumericalodispersion. e
Thedateralodiscretizationa Axo=a ye=e20cft)cfordheo,-ntireanodelearea,xoupledexithdhee
longitudinaladispersivitya)fc80cfeete ilecresultsdneaeGridd'ecletMumberaofCO.25dndheaentiree
modelearea. ceThedransversedateralodispersivitywfc8cfteresultseincacGridePecletalumberoDfe2.5,e
whicheisevellewithinetheodesirederange. e
Thewerticalodiscretizationeiswariablednocontrastdodhediorizontalodiscretization. eB ecauseca e
considerableeportionwfdhewarlydransporteindheemodeleisvertical, especialaconsiderationmfe
thisadiscretizationdsavarranted.00Grid(cellsd)eneathdheeashepondeindicateocelldhicknesseso Az)e
indayerse5 dhroughe7crangeefromeaboutel 2doe3 5 eft. wThedransverseeierticalodispersivity�av)dse
8.Oeftandheanodel.xThiso:esultsaneacgridcPeclet(numbero Pe_gride (Az/av)d:)etweeneaboutel.5e
ande4.4,ealsoe,vithindheedesirederangewfePecletaiumbers. eel.,ayercgehaseadhicknessewhiche
variesefromaboutcO.2dtdoe29eftdndhecsourcecarea. orThisxquatesdoeao: angeoDfwerticalegride
PecletcnumbersaDfcO.025 doe3.6. oeLayersc9candel Odiavecawonstantdhicknesswfc4Oeftewitheae
Pecletaiumberaofc5efor(yerticalodispersivity. xThuseallaDfdhecPecletaiumbersefordongitudinal,e
transverse,c ndwerticaledispersivityeareewithindheedesiredcrange.e
0
iii) Hydrologic framework — hydraulic properties

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Hydraulicq)ropertiesevereegroupedd)yanaterialdype�ash,edike,esaprolite,ealluvium,etransitione
zone,candd)edrock)oxvhichcareebasedoancslugetestscanddhediydrostratigraphyoofdheesitee
de scrib eddndheeC SAereport. eeThiscapproachdscreasonable. w
iv) Boundary conditions
Theemodeld:)oundaryeconditionsxonsistoafxonstantdleadseforetheeYadkineRivereandodrainsefore
thecannamedF-tributarieseanddowcareas. oeRechargeascapplieddne2¢onescatoratescDfe6anchescpere
yearefordheeashcbasinseande5 dnchescpereyearefordhecrestoofdheernodel. olo-flowd)oundariese
representcsurfaceodivides,exhichc recassumeddocalso(coincidesvithegroundwaterodivides.x
Theseeareeallereasonable.e
Theetransportemodeleusedoconstantoconcentrationeboundariesetodnputemass/concentratione
fromdheeashcbasins. eThesed)oundariesewereq)laceddndayersel ,e2cande3. cRechargeo,vasenote
usedetocaddoconcentrationdodheemodel. eThiseselectionaDfdransporternodeleboundarye
conditionsdlasetwo(potentialeramifications: e
• IfdhereeiseaegridepositionovithindheesimulatedesourceeareaexvhereeDneeoremoreocellse
areedrydneallcsourcedayers,dhenerechargeefromeinfiltrationethroughdheeashcbasineine
theseeareasexwillwnteretheemodelexithcaxoncentrationoofezero,ewhichewouldmoteagreee
withdheoconceptualemodeleforethisefacility. ofortunatelydhisodoesmotoaccureindhee
modelecalibration.e
• Theq)lacementoDferonstantxoncentration(cellsdbeneatheihecashq)ondemaydnhibitcthee
model'scabilityetoesimulateccapping,ebecausedateraleflowethroughetheseoconstante
concentrationeeellsavillocontinueetoeaddemass/concentrationdodheanodeleevene
thoughdeachingeandeinfiltrationemayebeegreatlyereducedebyethe(cap. cSimulationoafe
other(correctivecactions,00therdhanwxcavation,exwillcalsod)ycaffectedcbecausedhee
concentrationeaddeddodheemodelexillmotebecrepresentativeoofdheocappedefacility. e
v) Initial conditions in transient simulations
Theeflowemodeldscrundnesteadyestate,e,vherednitialoconditionsearemotcrelevanteapartefrome
numericaloconvergence,exvhichexwaseachieved. wThedransientetransportemodeleassumeseaezeroe
concentrationeinitially,ewithetheeashepondsmctingeascaoconstantoconcentrationesourcese
thereafter. eTheseanitialxonditionscareereasonable. w
vi) Convergence criteria and mass balance errors
ThedieaddoleranceandheeNWTq)ackagesoafel e-3asanoreethancadequateeinoensuringcheade
precisioncforethe(purposeseofdheemodel. wTheeflowemassebalanceediscrepancydndhee
MODFLOWeListingcfilewfcO.Oq)ercentasemoredhaneadequatedna-,nsuringaninimaleflowanasse
balancewrrors. wTheecumulativecconcentrationemass(balanceodiscrepancyefrom&lT3DMS dsw
lessethancO.4epercentcforoarseniceandcO.2epereenteford)oron. ceTheseanasscbalancewrrorscaree
moredhaneadequatedne.nsuringaninimaloconstituentanasscbalanceoerrors. e
e) Is the calibration done properly and adequately?

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e
Foreflowxalibrationdodieads,dhecN4eanekbsolute&rroraDverdhee^angedneobservedavaluesdse
7.1 cpercent,evhicheis�belowdheandustrycstandarda)fel0q)ereent. a:ThecscaledcRMSwrroreande
StandardDeviationeareeabouteg.7q)ercent,calsod)elowdheestandardoDfel Oepercent. adneaddition, e
thereeisetoesignificantespatialebiaseindheodistributionoo feresiduals. ae
Thedransport(ralibrationdsereasonableegivendheeuncertaintydnvolvedewithdhisdypeoofe
modeling. adnegeneral,ewellsewithehighoconcentrationscshowdiighesimulatedoconcentrationsefore
boroneandearsenic. oeLikewise,ewellseshowingdowdevels�orebelowadetection)calsowxhibitdowe
predictedeconcentrationseindheemodel.o-,Theernostenotablea-,xceptioneiseatewellscAB-2Sa layere
6)candeAB-2SLa layere7)avheredheemeasuredearsenicdsdiighestdndayero6.xTheemodeldiase
thesecreversed,(butdheehighestaconcentrationseareacomparableebetweendheeftelde
measurementscanddhe cmodelesimulated(values. e
Discretization of calibration parameters
Hydraulicq)ropertiese vereegroupedcbyanaterialdype�ash,adike,esaprolite,calluvium,etransitione
zone,candebedrock). aThisascaereasonablecapproach. oRechargeeisegroupedcbyanfiltratione
withindhecashebasinseandanutsidedheabasins.(eThisasealsoeaereasonableeapproach. e
i) Appropriateness of target as a metric of simulation objectives (e.g., calibrating
primarily to heads when transport is the primary purpose)
Thecflowanodelocalibrationdoeobserveddteadsaseadequate.oSeveral(plotsealsoeshowesimulatede
constituentaeoncentrationsdndhewontextanf(severaleobservedaconcentrations. oDetaileddablese
ofcDbservedcandesimulatedevoncentrationscarecalsocprovideddoodocumentdhedransporte
calibration.e
Is the sensitivity analysis conducted and if so, correctly?
i) Sensitivity Analysis approach (look for parameters which maybe insensitive to flow
but not to transport)
Aeflowemodelesensitivityeanalysisawaseconductedevherebyerechargeerates,epumpingerates,cande
hydraulicwonductivitieso,vereeperturbedeapmndodownebye20%. odtdsestateddhatavaterdevelse
areenostesensitivedodtorizontaldtydraulicoconductivitywfdheeshalloweaquifer,erechargee
outsidedhecashebasins, canddiydraulic wonductivity(ofdhedransition¢one. ceTheeresultsearee
depicteddneTablee4. aThi sdscaereasonableanethodeforeillustratingeflowemodelesensitivity. ac
Thedransportenodelesensitivityeanalysisdncludeddestingcsorptiono arsenicoonly)candq)orosity.
PorosityevaluesaofcO.2eandeO.3 overedestedealongavith&deforearsenicaDfc90eml/grameande45 e
ml/gram. aThisdseaereasonableemethodefordllustratingdransportenodelesensitivity.e
Model Files:
a) Can the model be run with the input files provided by the developer?
Yes. ce
b) Do the model results match those presented in the report?
i) Independent check of input data vs. conceptual model/report
Modeldnputseareeconsistentavithavhateisadescribedeinethecreport. e

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ii) Check of water balance vs. conceptual model
Thexonceptualanodeledoesalotepresenteaecomprehensiveaiumericaloxaterdbalance. e,Watere
entersctheanodeleasarechargedromcprecipitationeanddhearechargearatesmoteddndhea;onceptuale
modelcareeconsistentavithdhoseandheanodel.xTheeconstantdleadscalongctheeYadkineRivercaree
primarilycanwxitd7oundaryavhichdseconsistentavithdheeconceptualoxaterdbalance.oDrainse
repre sentingdributarycstreamscandevetlandsaremovedhearemainingarechargedevater. a e
iii) Independent check of model results vs. those reported
Independentlyegeneratedanodelaresultscarexonsistentevithevhatasod escribedanctheareport. e

Draft Groundwater Flow and Transport Model
Buck Steam Station
Rowan County, NC
Prepared for:
HDR Engineering, Inc.
Hydropower Services
440 S. Church St, Suite 1000
Charlotte, NC 28202
Investigators:
William G. Langley, Ph.D., P.E.
Dongwook Kim, Ph.D.
UNC Charlotte / Lee College of Engineering
Department of Civil and Environmental Engineering
EPIC Building 3252
9201 University City Blvd.
Charlotte, NC 28223
November 17, 2015

TABLE OF CONTENTS
1 Introduction...............................................................................................................................
1.1
General Setting and Background...................................................................................
1.2
Study Objectives............................................................................................................
2 Conceptual Model....................................................................................................................
2.1
Geology and Hydrogeology (HDR 2015).......................................................................
2.2
Hydrostratigraphic Layer Development (HDR 2015).....................................................
2.3
Ash Basins and Ash Storage Area (HDR 2015)............................................................
2.4
Groundwater Flow System.............................................................................................
2.5
Hydrologic Boundaries...................................................................................................
2.6
Hydraulic Boundaries.....................................................................................................
2.7
Sources and Sinks.........................................................................................................
2.8
Water Budget.................................................................................................................
2.9
Modeled Constituents of Interest (COI)..........................................................................
2.10
Constituent Transport.....................................................................................................
3 Computer Model.......................................................................................................................
3.1
Model Selection..............................................................................................................
3.2
Model Description...........................................................................................................
4 Groundwater Flow and Transport Model Construction............................................................
4.1
Model Hydrostratigraphy................................................................................................
4.2
GMS MODFLOW Version 10.........................................................................................
4.3
Model Domain and Grid.................................................................................................
4.4
Hydraulic Parameters.....................................................................................................
4.5
Flow Model Boundary Conditions..................................................................................
4.6
Flow Model Sources and Sinks......................................................................................
4.7
Flow Model Calibration Targets.....................................................................................
4.8
Transport Model Parameters.........................................................................................
4.9
Transport Model Boundary Conditions...........................................................................
4.10
Transport Model Sources and Sinks..............................................................................
4.11
Transport Model Calibration Targets..............................................................................
5 Model Calibration to Current Conditions..................................................................................
5.1
Flow Model Residual Analysis.......................................................................................
5.2
Flow Model Sensitivity Analysis.....................................................................................
5.3
Transport Model Calibration and Sensitivity...................................................................
6 Predictive
Simulations of Closure Scenarios...........................................................................
6.1
Existing Conditions Scenario.........................................................................................
6.2
Ash Basin Cap -in -Place Scenario..................................................................................
6.3
Excavation Scenario.......................................................................................................
7 Summary and Conclusions......................................................................................................
7.1
Model Assumptions and Limitations...............................................................................
1
1
2
2
2
2
4
6
6
6
6
6
7
7
7
7
7
.8
.8
.9
10
11
11
12
12
12
13
13
13
13
13
14
14
15
15
18
21
24
24
Appendix C

7.2 Model Predictions....................................................................................................................25
REFERENCES.................................................................................................................................. 26
Appendix C

TABLES
Table 1. Description of MODFLOW and MT3DMS Input Packages Utilized
Table 2. Hydraulic Conductivity in Model
Table 3. Observed vs. Predicted Hydraulic Head (ft msl)
Table 4. Effective Porosity in Model
Table 5. Transport Model Calibration Results
Table 6. Predicted Advective Travel Time Results
Table 7. Arsenic Transport Parameter Sensitivity Analysis
Table 8. Boron Transport Parameter Sensitivity Analysis
Appendix C

FIGURES
Figure 1. Conceptual Groundwater Flow Model/Model Domain
Figure 2. Model Domain North -South Cross Section (A -A') Through Secondary Ash Basin
Figure 3. Model Domain East-West Cross Section (B-B') Through Primary and Secondary Ash
Basins
Figure 4. Numerical Model Boundary Conditions
Figure 5. Model Recharge Areas and Contaminant Source Zones (Constant Concentration
Cells)
Figure 6. Observation Wells in Shallow Groundwater Zone
Figure 7. Observation Wells in Deep Groundwater Zone
Figure 8. Observation Wells in Bedrock Groundwater Zone
Figure 9. Hydraulic Conductivity Zonation in S/M1/M2 Layers (Model Layers 5-7)
Figure 10. Modeled Hydraulic Head (feet) vs. Observed Hydraulic Head (feet)
Figure 11. Hydraulic Head (feet) in M2 Saprolite Layer (Model Layer 7)
Figure 12. Hydraulic Head (feet) in North -South Cross Section (C-C') through Primary and
Secondary Ash Basins
Figure 13. Hydraulic Head (feet) in East-West Cross Section (C-C') through Primary and
Secondary Ash Basins
Figure 14 Particle Tracking Results (see Table. 6 for Advective Travel Times)
Figure 15. Predicted Antimony (pg/L) in Monitoring Well GWA-3S for Model Scenarios 1-3
Figure 16. Predicted Antimony (pg/L) in Monitoring Well GWA-4S for Model Scenarios 1-3
Figure 17. Predicted Antimony (pg/L) in Monitoring Well GWA-5S for Model Scenarios 1-3
Figure 18. Predicted Antimony (pg/L) in Monitoring Well GWA-12S for Model Scenarios 1-3
Figure 19. Predicted Antimony (pg/L) in Monitoring Well GWA-4D for Model Scenarios 1-3
Figure 20. Predicted Antimony (pg/L) in Monitoring Well GWA-9D for Model Scenarios 1-3
Figure 21. Predicted Antimony (pg/L) in Monitoring Well GWA-22D for Model Scenarios 1-3
Figure 22. Predicted Antimony (pg/L) in Monitoring Well GWA-3BRU for Model Scenarios 1-3
Figure 23. Predicted Antimony (pg/L) in Monitoring Well GWA-5BRU for Model Scenarios 1-3
Figure 24. Predicted Antimony (pg/L) in Monitoring Well GWA-12BRU for Model Scenarios 1-3
Figure 25. Predicted Boron (pg/L) in Monitoring Well GWA-3S for Model Scenarios 1-3
Figure 26. Predicted Boron (pg/L) in Monitoring Well GWA-5S for Model Scenarios 1-3
Figure 27. Predicted Boron (pg/L) in Monitoring Well GWA-9D for Model Scenarios 1-3
Figure 28. Predicted Boron (pg/L) in Monitoring Well GWA-22D for Model Scenarios 1-3
Figure 29. Predicted Boron (pg/L) in Monitoring Well GWA-3BRU for Model Scenarios 1-3
Figure 30. Predicted Boron (pg/L) in Monitoring Well GWA-513RU for Model Scenarios 1-3
Figure 31. Predicted Boron (pg/L) in Monitoring Well GWA-9BR for Model Scenarios 1-3
Appendix C iv

Figure 32. Predicted Chromium (pg/L) in Monitoring Well GWA-3S for Model Scenarios 1-3
Figure 33. Predicted Chromium (pg/L) in Monitoring Well GWA-5S for Model Scenarios 1-3
Figure 34. Predicted Chromium (pg/L) in Monitoring Well GWA-12S for Model Scenarios 1-3
Figure 35. Predicted Chromium (pg/L) in Monitoring Well GWA-41D for Model Scenarios 1-3
Figure 36. Predicted Chromium (pg/L) in Monitoring Well GWA-3BRU for Model Scenarios 1-3
Figure 37. Predicted Chromium (pg/L) in Monitoring Well GWA-5BRU for Model Scenarios 1-3
Figure 38. Predicted Chromium (pg/L) in Monitoring Well GWA-12BRU for Model Scenarios 1-3
Figure 39. Predicted Cobalt (pg/L) in Monitoring Well GWA-3S for Model Scenarios 1-3
Figure 40. Predicted Cobalt (fag/L) in Monitoring Well GWA-4S for Model Scenarios 1-3
Figure 41. Predicted Cobalt (pg/L) in Monitoring Well GWA-5S for Model Scenarios 1-3
Figure 42. Predicted Cobalt (pg/L) in Monitoring Well GWA-9S for Model Scenarios 1-3
Figure 43. Predicted Cobalt (pg/L) in Monitoring Well GWA-12S for Model Scenarios 1-3
Figure 44. Predicted Cobalt (pg/L) in Monitoring Well GWA-41D for Model Scenarios 1-3
Figure 45. Predicted Cobalt (pg/L) in Monitoring Well GWA-91D for Model Scenarios 1-3
Figure 46. Predicted Cobalt (pg/L) in Monitoring Well GWA-22D for Model Scenarios 1-3
Figure 47. Predicted Cobalt (pg/L) in Monitoring Well GWA-3BRU for Model Scenarios 1-3
Figure 48. Predicted Cobalt (pg/L) in Monitoring Well GWA-5BRU for Model Scenarios 1-3
Figure 49. Predicted Cobalt (pg/L) in Monitoring Well GWA-12BRU for Model Scenarios 1-3
Figure 50. Predicted Hexavalent Chromium (pg/L) in Monitoring Well GWA-3S for Model
Scenarios 1-3
Figure 51. Predicted Hexavalent Chromium (pg/L) in Monitoring Well GWA-4S for Model
Scenarios 1-3
Figure 52. Predicted Hexavalent Chromium (pg/L) in Monitoring Well GWA-5S for Model
Scenarios 1-3
Figure 53. Predicted Hexavalent Chromium (pg/L) in Monitoring Well GWA-41D for Model
Scenarios 1-3
Figure 54. Predicted Hexavalent Chromium (pg/L) in Monitoring Well GWA-91D for Model
Scenarios 1-3
Figure 55. Predicted Hexavalent Chromium (pg/L) in Monitoring Well GWA-22D for Model
Scenarios 1-3
Figure 56. Predicted Hexavalent Chromium (pg/L) in Monitoring Well GWA-3BRU for Model
Scenarios 1-3
Figure 57. Predicted Hexavalent Chromium (pg/L) in Monitoring Well GWA-5BRU for Model
Scenarios 1-3
Figure 58. Predicted Sulfate (pg/L) in Monitoring Well GWA-41D for Model Scenarios 1-3
Figure 59. Predicted Sulfate (fag/L) in Monitoring Well GWA-91D for Model Scenarios 1-3
Figure 60. Predicted Sulfate (pg/L) in Monitoring Well GWA-5BRU for Model Scenarios 1-3
Appendix C v

Figure 61. Predicted Sulfate (pg/L) in Monitoring Well GWA-9BR for Model Scenarios 1-3
Figure 62. Predicted Vanadium (pg/L) in Monitoring Well GWA-3S for Model Scenarios 1-3
Figure 63. Predicted Vanadium (pg/L) in Monitoring Well GWA-4S for Model Scenarios 1-3
Figure 64. Predicted Vanadium (pg/L) in Monitoring Well GWA-5S for Model Scenarios 1-3
Figure 65. Predicted Vanadium (pg/L) in Monitoring Well GWA-9S for Model Scenarios 1-3
Figure 66. Predicted Vanadium (pg/L) in Monitoring Well GWA-12S for Model Scenarios 1-3
Figure 67. Predicted Vanadium (pg/L) in Monitoring Well GWA-4D for Model Scenarios 1-3
Figure 68. Predicted Vanadium (pg/L) in Monitoring Well GWA-9D for Model Scenarios 1-3
Figure 69. Predicted Vanadium (pg/L) in Monitoring Well GWA-22D for Model Scenarios 1-3
Figure 70. Predicted Vanadium (pg/L) in Monitoring Well GWA-3BRU for Model Scenarios 1-3
Figure 71. Predicted Vanadium (pg/L) in Monitoring Well GWA-5BRU for Model Scenarios 1-3
Figure 72. Predicted Vanadium (pg/L) in Monitoring Well GWA-9BR for Model Scenarios 1-3
Figure 73. Predicted Vanadium (pg/L) in Monitoring Well GWA-12BRU for Model Scenarios 1-3
Figure 74. Initial (2015) Antimony Concentrations (pg/L) in the Shallow Groundwater Zone
Figure 75. Initial (2015) Antimony Concentrations (pg/L) in the Deep Groundwater Zone
Figure 76. Initial (2015) Antimony Concentrations (pg/L) in the Bedrock Groundwater Zone
Figure 77. "Existing" Scenario 1 - 2115 Predicted Antimony (pg/L) in the Shallow Groundwater
Zone
Figure 78. "Existing" Scenario 1 - 2115 Predicted Antimony (pg/L) in the Deep Groundwater
Zone
Figure 79. "Existing" Scenario 1 - 2115 Predicted Antimony (pg/L) in the Bedrock Groundwater
Zone
Figure 80. "Cap -In -Place" Scenario 2 - 2115 Predicted Antimony (pg/L) in the Shallow
Groundwater Zone
Figure 81. "Cap -In -Place" Scenario 2 - 2115 Predicted Antimony (pg/L) in the Deep Groundwater
Zone
Figure 82. "Cap -In -Place" Scenario 2 - 2115 Predicted Antimony (pg/L) in the Bedrock
Groundwater Zone
Figure 83. "Excavate" Scenario 3 - 2115 Predicted Antimony (pg/L) in the Shallow Groundwater
Zone
Figure 84. "Excavate" Scenario 3 - 2115 Predicted Antimony (pg/L) in the Deep Groundwater
Zone
Figure 85. "Excavate" Scenario 3 - 2115 Predicted Antimony (pg/L) in the Bedrock Groundwater
Zone
Figure 86. Initial (2015) Boron Concentrations (pg/L) in the Shallow Groundwater Zone
Figure 87. Initial (2015) Boron Concentrations (pg/L) in the Deep Groundwater Zone
Figure 88. Initial (2015) Boron Concentrations (pg/L) in the Bedrock Groundwater Zone
Appendix C vi

Figure 89. "Existing" Scenario 1 - 2115 Predicted Boron (pg/L) in the Shallow Groundwater
Zone
Figure 90. "Existing" Scenario 1 - 2115 Predicted Boron (pg/L) in the Deep Groundwater
Zone
Figure 91. "Existing" Scenario 1 - 2115 Predicted Boron (pg/L) in the Bedrock Groundwater
Zone
Figure 92. "Cap -In -Place" Scenario 2 - 2115 Predicted Boron (pg/L) in the Shallow
Groundwater Zone
Figure 93. "Cap -In -Place" Scenario 2 - 2115 Predicted Boron (pg/L) in the Deep Groundwater
Zone
Figure 94. "Cap -In -Place" Scenario 2 - 2115 Predicted Boron (pg/L) in the Bedrock
Groundwater Zone
Figure 95. "Excavate" Scenario 3 - 2115 Predicted Boron (pg/L) in the Shallow Groundwater
Zone
Figure 96. "Excavate" Scenario 3 - 2115 Predicted Boron (pg/L) in the Deep Groundwater
Zone
Figure 97. "Excavate" Scenario 3 - 2115 Predicted Boron (pg/L) in the Bedrock Groundwater
Zone
Figure 98. Initial (2015) Chromium Concentrations (pg/L) in the Shallow Groundwater Zone
Figure 99. Initial (2015) Chromium Concentrations (pg/L) in the Deep Groundwater Zone
Figure 100. Initial (2015) Chromium Concentrations (pg/L) in the Bedrock Groundwater Zone
Figure 101. "Existing" Scenario 1 - 2115 Predicted Chromium (pg/L) in the Shallow Groundwater
Zone
Figure 102. "Existing" Scenario 1 - 2115 Predicted Chromium (pg/L) in the Deep Groundwater
Zone
Figure 103. "Existing" Scenario 1 - 2115 Predicted Chromium (pg/L) in the Bedrock Groundwater
Zone
Figure 104. "Cap -In -Place" Scenario 2 - 2115 Predicted Chromium (pg/L) in the Shallow
Groundwater Zone
Figure 105. "Cap -In -Place" Scenario 2 - 2115 Predicted Chromium (pg/L) in the Deep
Groundwater Zone
Figure 106. "Cap -In -Place" Scenario 2 - 2115 Predicted Chromium (pg/L) in the Bedrock
Groundwater Zone
Figure 107. "Excavate" Scenario 3 - 2115 Predicted Chromium (pg/L) in the Shallow Groundwater
Zone
Figure 108. "Excavate" Scenario 3 - 2115 Predicted Chromium (pg/L) in the Deep Groundwater
Zone
Figure 109. "Excavate" Scenario 3 - 2115 Predicted Chromium (pg/L) in the Bedrock Groundwater
Zone
Figure 110. Initial (2015) Cobalt Concentrations (pg/L) in the Shallow Groundwater Zone
Figure 111. Initial (2015) Cobalt Concentrations (pg/L) in the Deep Groundwater Zone
Appendix C vii

Figure 112. Initial (2015) Cobalt Concentrations (pg/L) in the Bedrock Groundwater Zone
Figure 113. "Existing" Scenario 1 - 2115 Predicted Cobalt (pg/L) in the Shallow Groundwater Zone
Figure 114. "Existing" Scenario 1 - 2115 Predicted Cobalt (pg/L) in the Deep Groundwater Zone
Figure 115. "Existing" Scenario 1 - 2115 Predicted Cobalt (pg/L) in the Bedrock Groundwater
Zone
Figure 116. "Cap -In -Place" Scenario 2 - 2115 Predicted Cobalt (pg/L) in the Shallow Groundwater
Zone
Figure 117. "Cap -In -Place" Scenario 2 - 2115 Predicted Cobalt (pg/L) in the Deep Groundwater
Zone
Figure 118. "Cap -In -Place" Scenario 2 - 2115 Predicted Cobalt (pg/L) in the Bedrock Groundwater
Zone
Figure 119. "Excavate" Scenario 3 - 2115 Predicted Cobalt (pg/L) in the Shallow Groundwater
Zone
Figure 120. "Excavate" Scenario 3 - 2115 Predicted Cobalt (pg/L) in the Deep Groundwater Zone
Figure 121. "Excavate" Scenario 3 - 2115 Predicted Cobalt (pg/L) in the Bedrock Groundwater
Zone
Figure 122. Initial (2015) Hexavalent Chromium Concentrations (pg/L) in the Shallow
Groundwater Zone
Figure 123. Initial (2015) Hexavalent Chromium Concentrations (pg/L) in the Deep Groundwater
Zone
Figure 124. Initial (2015) Hexavalent Chromium Concentrations (pg/L) in the Bedrock
Groundwater Zone
Figure 125. "Existing" Scenario 1 - 2115 Predicted Hexavalent Chromium (pg/L) in the Shallow
Groundwater Zone
Figure 126. "Existing" Scenario 1 - 2115 Predicted Hexavalent Chromium (pg/L) in the Deep
Groundwater Zone
Figure 127. "Existing" Scenario 1 - 2115 Predicted Hexavalent Chromium (pg/L) in the Bedrock
Groundwater Zone
Figure 128. "Cap -In -Place" Scenario 2 - 2115 Predicted Hexavalent Chromium (pg/L) in the
Shallow Groundwater Zone
Figure 129. "Cap -In -Place" Scenario 2 - 2115 Predicted Hexavalent Chromium (pg/L) in the Deep
Groundwater Zone
Figure 130. "Cap -In -Place" Scenario 2 - 2115 Predicted Hexavalent Chromium (pg/L) in the
Bedrock Groundwater Zone
Figure 131. "Excavate" Scenario 3 - 2115 Predicted Hexavalent Chromium (pg/L) in the Shallow
Groundwater Zone
Figure 132. "Excavate" Scenario 3 - 2115 Predicted Hexavalent Chromium (pg/L) in the Deep
Groundwater Zone
Figure 133. "Excavate" Scenario 3 - 2115 Predicted Hexavalent Chromium (pg/L) in the Bedrock
Groundwater Zone
Figure 134. Initial (2015) Sulfate Concentrations (pg/L) in the Shallow Groundwater Zone
Appendix C viii

Figure 135. Initial (2015) Sulfate Concentrations (pg/L) in the Deep Groundwater Zone
Figure 136. Initial (2015) Sulfate Concentrations (pg/L) in the Bedrock Groundwater Zone
Figure 137. "Existing" Scenario 1 - 2115 Predicted Sulfate (pg/L) in the Shallow Groundwater
Zone
Figure 138. "Existing" Scenario 1 - 2115 Predicted Sulfate (pg/L) in the Deep Groundwater Zone
Figure 139. "Existing" Scenario 1 - 2115 Predicted Sulfate (pg/L) in the Bedrock Groundwater
Zone
Figure 140. "Cap -In -Place" Scenario 2 - 2115 Predicted Sulfate (pg/L) in the Shallow Groundwater
Zone
Figure 141. "Cap -In -Place" Scenario 2 - 2115 Predicted Sulfate (pg/L) in the Deep Groundwater
Zone
Figure 142. "Cap -In -Place" Scenario 2 - 2115 Predicted Sulfate (pg/L) in the Bedrock
Groundwater Zone
Figure 143. "Excavate" Scenario 3 - 2115 Predicted Sulfate (pg/L) in the Shallow Groundwater
Zone
Figure 144. "Excavate" Scenario 3 - 2115 Predicted Sulfate (pg/L) in the Deep Groundwater Zone
Figure 145. "Excavate" Scenario 3 - 2115 Predicted Sulfate (pg/L) in the Bedrock Groundwater
Zone
Figure 146. Initial (2015) Vanadium Concentrations (pg/L) in the Shallow Groundwater Zone
Figure 147. Initial (2015) Vanadium Concentrations (pg/L) in the Deep Groundwater Zone
Figure 148. Initial (2015) Vanadium Concentrations (pg/L) in the Bedrock Groundwater Zone
Figure 149. "Existing" Scenario 1 - 2115 Predicted Vanadium (pg/L) in the Shallow Groundwater
Zone
Figure 150. "Existing" Scenario 1 - 2115 Predicted Vanadium (pg/L) in the Deep Groundwater
Zone
Figure 151. "Existing" Scenario 1 - 2115 Predicted Vanadium (pg/L) in the Bedrock Groundwater
Zone
Figure 152. "Cap -In -Place" Scenario 2 - 2115 Predicted Vanadium (pg/L) in the Shallow
Groundwater Zone
Figure 153. "Cap -In -Place" Scenario 2 - 2115 Predicted Vanadium (pg/L) in the Deep
Groundwater Zone
Figure 154. "Cap -In -Place" Scenario 2 - 2115 Predicted Vanadium (pg/L) in the Bedrock
Groundwater Zone
Figure 155. "Excavate" Scenario 3 - 2115 Predicted Vanadium (pg/L) in the Shallow Groundwater
Zone
Figure 156. "Excavate" Scenario 3 - 2115 Predicted Vanadium (pg/L) in the Deep Groundwater
Zone
Figure 157. "Excavate" Scenario 3 - 2115 Predicted Vanadium (pg/L) in the Bedrock
Groundwater Zone
Appendix C ix

1 INTRODUCTION
The calibrated flow and transport model third -party peer review team was coordinated by EPRI and
included Dr. Chunmiao Zheng from the University of Alabama, James Rumbaugh from
Environmental Simulations, Inc, and experienced modelers from Intera, Inc.
The reviewers were provided with the CSA, a draft model report, and digital model input and output
files, allowing them to reconstruct the model for independent review. During the course of the review,
the reviewers communicated with the modelers in order to better understand how the model was
developed and calibrated. The reviewers concluded that the model was constructed and calibrated
sufficiently to achieve its primary objective of comparing the effects of closure alternatives on nearby
groundwater quality. In addition, the reviewers identified limitations with the model, which are
included in the discussion of model limitations later in this documentation.
1.1 General Setting and Background
Duke Energy owns the Buck Steam Station, located on a 640-acre tract on the Yadkin River in
Rowan County near the town of Salisbury, North Carolina. Buck began operation in 1926 as a coal-
fired generating station. The Buck Combined Cycle Station (BCCS) natural gas facility was
constructed at the site and began operating in late 2011. Subsequently, Buck was decommissioned
and taken offline in April 2013. The coal ash residue from Buck's coal combustion process was
historically disposed of in the station's ash basin system located adjacent to the station and the
Yadkin River (HDR Figures 2-2 and 2-4).
Buck was a six -unit coal-fired electricity generating facility along the Yadkin River. Buck began
operation of Units 1 and 2 in 1926 as a coal-fired generating station with a capacity of
256 megawatts (MW). Units 1 and 2 were retired in 1979. Units 3 and 4 at Buck, 113 MW combined,
were retired in mid-2011 and Units 5 and 6, 143 MW combined, were retired in April 2013. There are
no coal-fired units currently in operation at Buck. Construction of the 620-MW BCCS natural gas
facility began in 2008. Commercial operation of the natural gas facility began in late 2011. Three
combustion turbine units formerly operated adjacent to the coal-fired units and were retired in
October 2012. Buildings and other structures associated with power production are generally located
in the northwestern section of the site. The eastern portion of the site is generally wooded with the
exception of the remaining ponded areas of the ash basin. Refer to HDR Figures 2-2 and 2-4 for
maps of the site layout and features.
Topography at the Buck site ranges from an approximate high elevation of 734 feet (NAVD 88) at
the communications cell tower near the southwest edge of the property to an approximate low
elevation of 620 feet at the Yadkin River on the northern margin of the site, with a total elevation
change of approximately 114 feet over an approximate distance of 0.9 miles. Surface water drainage
flow generally follows site topography from the south to north across the site except where natural
drainage patterns have been modified by the ash basin or other construction features.
Based on the Comprehensive Site Assessment (CSA) site investigation (HDR 2015), the
groundwater system in the natural materials (alluvium, soil, soil/saprolite, and fractured bedrock) at
Buck is consistent with the Piedmont regolith-fractured rock system and is an unconfined, connected
system of three flow layers (HDR Figure 5-5). In general, groundwater within the shallow, deep
transition zone (TZ), and bedrock layers flows radially from the ash basins and northward toward the
Yadkin River.
Appendix C 1

1.2 Study Objectives
The purpose of this study is to predict the groundwater flow and constituent transport that will occur
as a result of different possible corrective actions at the site. The study consists of three main
activities: development of a calibrated steady-state flow model of current conditions, development of
a historical transient model of constituent transport that is calibrated to current conditions, and
predictive simulations of the different corrective action options.
2 CONCEPTUAL MODEL
The site conceptual model for Buck is primarily based on the Comprehensive Site Assessment
Report (CSA Report) for the Buck Steam Station (HDR 2015). The CSA report contains extensive
detail and data related to most aspects of the site conceptual model that are used here. The
conceptual model, model domain and cross sections though the ash basins are shown in Figures 1-
3.
2.1 Geology and Hydrogeology (HDR 2015)
The Buck site is within the Charlotte terrane, one of a number of tectonostratigraphic terranes that
have been defined in the southern and central Appalachians and is in the western portion of the
larger Carolina superterrane (HDR Figure 5-1). On the northwest side, the Charlotte terrane is in
contact with the Inner Piedmont zone along the Central Piedmont suture along its northwest
boundary and is distinguished from the Carolina terrane to the southeast by its higher metamorphic
grade and portions of the boundary may be tectonic (HDR 2015).
The fractured bedrock is overlain by a mantle of unconsolidated material known as regolith. The
regolith includes residual soil and saprolite zones and, where present, alluvial deposits. Saprolite,
the product of chemical weathering of the underlying bedrock, is typically composed of clay and
coarser granular material and reflects the texture and structure of the rock from which it was formed.
The weathering products of granitic rocks are quartz -rich and sandy textured. Rocks poor in quartz
and rich in feldspar and ferro-magnesium minerals form a more clayey saprolite.
Therefore, the groundwater system is a two -medium system generally restricted to the local
drainage basin (HDR 2015). The groundwater occurs in a system composed of two interconnected
layers: residual soil/saprolite and weathered rock overlying fractured sedimentary rock. The systems
are separated by the transition zone portion (TZ) of the residual soil, saprolite, and weathered rock.
Typically, the residual soil/saprolite is partially saturated and the water table fluctuates within it.
Water movement is generally preferential through the weathered/fractured and fractured bedrock of
the TZ (i.e., enhanced permeability zone). The character of such aquifers results from the combined
effects of the rock type, fracture system, topography, and weathering. Topography exerts an
influence on both weathering and the opening of fractures, while the weathering of the crystalline
rock modifies both transmissive and storage characteristics.
2.2 Hydrostratigraphic Layer Development (HDR 2015)
The following materials were encountered during the site exploration and are consistent with
material descriptions from previous site exploration studies:
Ash — Ash was encountered in borings advanced within the ash basin and ash storage areas, as
well as through dikes. Ash was generally described as gray to dark gray, non -plastic, loose to
medium dense, dry to wet, fine to coarse -grained.
Appendix C

Fill — Fill material generally consisted of re -worked silts, clays, and sands that were borrowed from
one area of the site and re -distributed to other areas. Fill was generally classified as silty sand, clay
with sand, clay, and sandy clay on the boring logs. Fill was used in the construction of dikes, and as
cover for ash storage area.
Alluvium — Alluvium encountered in borings during the project was classified as clay and sand with
clay. In some cases alluvium was logged beneath ash.
Residuum (Residual soils) — Residuum is the in -place weathered soil that consists primarily of silt
with sand, clayey sand, sandy clay, clay with gravel, and clayey silts. Residuum varied in thickness
and was relatively thin compared to the thickness of saprolite.
Saprolite/Weathered Rock — Saprolite is soil developed by in -place weathering of rock that retains
remnant bedrock structure. Saprolite consists primarily of medium dense to very dense silty sand,
sandy silt, sand, sand with gravel, sand with clay, clay with sand, and clay. Sand particle size ranges
from fine to coarse grained. Much of the saprolite is micaceous.
Partially Weathered/Fractured Rock — Partially weathered (slight to moderate) and/or highly
fractured rock encountered below auger refusal.
Bedrock — Sound rock in boreholes, were generally slightly weathered to fresh and relatively
unfractured.
Based on the CSA, the groundwater system is consistent with the regolith-fractured bedrock system.
To define the hydrostratigraphic units, a classification system used to show that the TZ is present in
the Piedmont groundwater system was modified to define the hydrostratigraphic layers of the natural
groundwater system (HDR 2015). The classification system is based on Standard Penetration
Testing values (N) and the Recovery (REC) and Rock Quality Designation (RQD) collected during
the drilling and logging of the boreholes.
The ash, fill, and alluvial layers are as encountered at the site. The natural system (except alluvium)
includes the following layers:
• M1 — Soil/Saprolite: N<50
• M2 — Saprolite/Weathered Rock: N>50 or REC<50%
• TZ — Transition Zone: REC>50% and RQD<50%
• BR — Bedrock: REC>85% and RQD>50%.
Rock core runs that fell between the values for TZ and BR (REC<85% and RQD>50% or REC>85%
and RQD<50%) were assigned a hydrostratigraphic layer based on a review of the borehole logs,
rock core photographs, and geologic judgment. The same review was performed in making the final
determination of the thickness of the TZ as it could extend into the next core run that meets the BR
criterion because of potential core loss or fractured/jointed rock with indications of water movement
(iron/manganese staining).
The above layer designations (M1, M2, TZ, and BR) are used on the geologic cross -sections with
transect locations shown on HDR Figure 11-1. The ash, fill, and alluvial layers are represented by A,
F, and S, respectively on the cross -sections and tables.
Appendix C

Ranges of hydrostratigraphic layer properties measured at Buck are provided in HDR Tables 11-7
through 11-11.
2.3 Ash Basins and Ash Storage Area (HDR 2015)
Historical and current information about the Buck ash basin system assembled by HDR (2015) is
relevant to developing the conceptual and numerical groundwater flow models. Refer to HDR
Figures 2-2 and 2-4 for locations of ash basin system components described as follows.
The Buck ash basin system is located near the Yadkin River and comprises three cells designated
as Cell 1, Cell 2, and Cell 3, and associated embankments and outlet works. The ash basin is
located to the south (Cell 1) and southeast (Cells 2 and 3) of the retired Buck Units 1 through 6 and
the BCCS. An area between Cell 1 and Cell 2 has also been utilized for storage of dredged ash from
Cell 1 and is referred to as the ash storage area. Buck historically produced approximately 100,000
tons of ash per year.
Ash Basin
The original ash basin at Buck began operation in 1957 and was formed by constructing a dam
across a tributary of the Yadkin River with a crest elevation of 680 feet. The footprint of the original
ash basin was the approximate current footprint of Cells 2 and 3. As the ash basin capacity
diminished over time, the original basin was eventually divided into two ash basins (Cells 2 and 3) by
construction of a separate intermediate dike over ash and raising the elevation of the western portion
of the earthen dike along the Yadkin River by 10 feet in 1977.
In 1982, additional storage was created by construction of Cell 1, separate and upgradient from Cell
2, by building a new dike with a crest elevation of 710 feet. Until Cell 1 was constructed, ash
generated from the coal combustion process at Buck was sluiced (via ash discharge lines) into the
northwest section of Cell 2. Following construction of Cell 1, discharge of sluiced ash into the ash
basin system was rerouted from Cell 2 to the northeast section of Cell 1.
All coal ash from Buck was disposed of in the ash basin from approximately 1957 until 2013. Fly ash
precipitated from flue gas, and bottom ash collected in the bottom of the boilers were sluiced to the
ash basin using conveyance water withdrawn from the Yadkin River.
The discharge flow from Cell 1 enters Cell 2 via the Cell 1 discharge tower. Flow from Cell 2 enters
Cell 3 via the Cell 2 discharge tower. Flow is discharged through NPDES Outfall 002 to the Yadkin
River through the Cell 3 discharge tower located at the north end of Cell 3. The Cell 3 concrete
discharge tower drains through a 36-inch-diameter corrugated metal pipe.
The approximate current basin elevations (obtained June 2015) for the three ash basin cells are:
Cell 1 — pond elevation 701 feet; Cell 2 — pond elevation 682 feet; Cell 3 — pond elevation 673 feet.
The elevation of the Yadkin River near the site is approximately 620 feet. The ash basin pond
elevations are controlled by the use of concrete stop logs in the three discharge towers.
The area contained within the waste boundary for Cell 1 encompasses approximately 90 acres. For
purposes of delineating the waste boundary, Cells 2 and 3 are considered a single unit, with the area
contained within this portion of the waste boundary encompassing approximately 80.7 acres. The
ash basin waste boundary is shown on HDR Figure 2-2.
Appendix C 4

The quantity of ash contained within the ash basin was estimated by comparing the digitized pre -
basin topographic survey of the site to a topographic and bathymetric survey of the basin, dated
November 2013, which was after the last coal-fired generating unit was retired. The estimated in -
place quantities of ash are: Cell 1 — 2,366,000 cubic yards (cy), Cell 2 — 1,624,000 cy, and Cell 3 —
227,000 cy. Actual ash quantities may vary from those calculated since soil borrow operations are
known to have taken place within the ash basin boundaries prior to the deposition of ash.
During operation of the coal-fired units, the ash basin received variable inflows from the ash removal
system and other permitted discharges. Currently, the ash basin receives variable inflows from the
station yard drain sump, storm water flows, and BCCS wastewater and no longer receives sluiced
ash.
Cell 3 and the southern portion of Cell 2 continue to serve as treatment units for the ash basin
system. Trees and other vegetation have naturally established in the northern portion of Cell 2. The
water level within Cell 1 has been lowered such that there is relatively little ponding occurring within
the cell.
Ash Storage Area
An unlined ash storage area is located topographically upgradient and adjacent to the east side of
Cell 1 (HDR Figure 2-2). The dry ash storage area covers approximately 14 acres and was
constructed in 2009 by excavating ash within the eastern half of Cell 1 in order to provide additional
capacity for sluiced ash. Following the completion of excavation and stockpiling, the dry ash storage
area was graded to drain to Cell 1 and a minimum of 18 and 24 inches of soil cover were placed on
the top slopes and side slopes, respectively, and vegetation was established. The estimated in -place
quantity of ash stored at this location is 209,000 cy based on a comparison of original site
topography and the topographic survey of the site from November 2013.
Dams
There are five regulated earthen dams within the Buck ash basin system. These include the Cell
2/Cell 3 main dam located adjacent to the Yadkin River, the Cell 1 dam located south of the BCCS,
an intermediate dam that divides Cell 2 and Cell 3, and the small dams associated with the Cell 1
and Cell 2 discharge towers. Dams are also referred to as dikes in this report.
The Cell 2/Cell 3 main dam was constructed in 1956 and was formed by constructing a dam across
a tributary of the Yadkin River with a crest elevation of 680 feet and a total height at its deepest point
of approximately 60 feet. As the ash basin capacity diminished over time, the original basin was
eventually divided into two cells (Cells 2 and 3) by construction of a separate intermediate dike over
ash and raising the elevation of the western portion of the earthen dike along the Yadkin River by 10
feet (in 1977). At this same time, the canal for the Cell 2 discharge tower was excavated and the
dam associated with the discharge tower was constructed with a base elevation at 670 feet and a
crest elevation of 690 feet. In 1979, the intermediate dam dividing Cell 2 and Cell 3 was reinforced
by constructing an earthen embankment with a crest elevation of 682 feet over ash on the
downstream side of the dam. The embankment has a washed stone blanket drain between the soil
and underlying ash.
In 1982, additional storage was created by construction of Cell 1 dam with a crest elevation of 710
feet and a total height at its deepest point of approximately 60 feet. At this same time, the canal for
Appendix C

the Cell 1 discharge tower was excavated and the dam associated with the discharge tower was
constructed with a base elevation at 685 feet and a crest elevation of 710 feet.
2.4 Groundwater Flow System
Groundwater is recharged by infiltration where the ground surface is permeable, including the dikes
and ash of the ash basin system where exposed at the ground surface. After infiltrating the ground
surface, water in the unsaturated zone percolates downward to the unconfined water table, except
where ponded water conditions exists on a portion on the secondary cell of the ash basin system.
From the water table, groundwater moves downward and laterally through unconsolidated material
(residual soil/saprolite) into the weathered, fractured rock, then into fractured bedrock. Mean annual
recharge in the Piedmont ranges from 4.0 to 9.7 inches per year (Daniel 2001).
Given that it has not been measured or estimated in the CSA or other studies of the site, recharge to
the ash basin system was estimated by considering it as a calibration parameter in the groundwater
flow model.
Based on the CSA (HDR 2015), the groundwater system in the natural materials (alluvium, soil,
soil/saprolite, and bedrock) at Buck is consistent with the Piedmont regolith-fractured rock system
and is an unconfined, connected system of three flow layers. Groundwater at the Buck site generally
flows from south to north toward to the Yadkin River with components of flow to the east and west
toward unnamed tributaries to the Yadkin River located near the eastern and western extents of the
site (HDR Figures 6-5, 6-6, and 6-7). Steep horizontal hydraulic gradients in the water table wells
and deep wells are associated with flows through the low -conductivity ash basin dikes.
In accordance with the Piedmont Slope Aquifer System of LeGrand (2004), bedrock fractured
density decreases with depth, limiting deep groundwater flow (HDR Figure 5-5). In the groundwater
flow model, fractured bedrock was simulated as an equivalent porous medium.
2.5 Hydrologic Boundaries
The major discharge location for the groundwater system at Buck, the Yadkin River, serves as a
hydrologic boundary. Local ditches and streams also serve as local, shallow hydrologic boundaries.
In the flow model, these smaller features are treated as internal water sink terms.
2.6 Hydraulic Boundaries
The groundwater flow system at Buck does not contain impermeable barriers or boundaries with the
exception of bedrock at depth where fracture density is minimal. Natural groundwater divides exist
along topographic divides but are a result of local flow conditions as opposed to barriers.
2.7 Sources and Sinks
Recharge, including that to the ash basins, is the major source of water to the groundwater system.
Most of this water discharges to the hydrologic boundaries described above. One hundred sixty six
private water supply wells and two public water supply wells within a half -mile radius of the site were
identified in the CSA (HDR 2015). The CSA does not consider if the Buck study area is within the
capture zone or zone of influence of any extraction well or wells.
2.8 Water Budget
Over an extended period of time, the rate of water inflow to the study area is equal to its rate of
water outflow. That is, there is no change in groundwater storage. Water enters the groundwater
system through recharge and ultimately discharges to the Yadkin River.
Appendix C

2.9 Modeled Constituents of Interest (COI)
As defined in the CSA, the metals, compounds (or constituents) that were identified in the
groundwater assessment plans for sampling and analysis (HDR 2015) are potential COIs. The
following criteria were used to determine if a COI required modeling: if the constituent exceeded
regulatory groundwater standards (15A NCAC 02L.0202 groundwater standard or interim maximum
allowable concentration [IMAC]), formed a continuous and identifiable plume in groundwater, and is
traceable back to the source (i.e., existed in porewater) - the constituent was then deemed a COI for
transport modeling. Per the CSA, the metals that were detected in ash basin porewater are;
antimony, arsenic, barium, boron, cobalt, iron, manganese, thallium, and vanadium. Since boron,
antimony, cobalt, sulfate and vanadium form continuous plumes in groundwater and exist in
porewater, transport modeling was performed for these COIs.
2.10 Constituent Transport
COls entered the ash basin system in the dissolved phase and solid phase of the station's
wastewater discharge. Some constituents are also present in native soils and groundwater beneath
the basin. In the ash basin, constituents may incur phase changes including dissolution,
precipitation, adsorption, and desorption. Dissolved phase constituents may incur these phase
changes as they are transported in groundwater flowing downgradient from the basin. In the fate and
transport model, chemical constituents enter the basin in the dissolved phase by specifying a
steady-state concentration in the ash pore water. Phase changes (dissolution, precipitation,
adsorption, and desorption) are collectively taken into account by specifying a linear sorption
coefficient Kd. The accumulation and subsequent release of chemical constituents in the ash basin
over time is a complex process. In the conceptual fate and transport model, it was assumed that the
entry of constituents into the ash basin is represented by a constant concentration in the saturated
zone of the basin which is continually flushed by infiltrating recharge from above.
3 COMPUTER MODEL
3.1 Model Selection
The computer code MODFLOW solves the system of equations that quantify the flow of groundwater
in three dimensions. MODFLOW can simulate steady-state and transient flow, as well as confined
and water table conditions. Additional components of groundwater can be considered including
pumping wells, recharge, evapotranspiration, rivers, streams, springs, and lakes. The information
assembled in the conceptual site model is translated into its numerical equivalent from which a
solution is generated by MODFLOW.
3.2 Model Description
The specific MODFLOW package chosen for the study is NWT - a Newton formulation of
MODFLOW-2005 that is specifically designed for improving the stability of solutions involving drying
and re -wetting under water table conditions (Niswonger, et al. 2011). The numerical code selected
for the transport model is MT3DMS (Zheng and Wang 1999). MT3DMS is multi -species three-
dimensional transport model that can simulate advection, dispersion/diffusion, and chemical reaction
of COls in groundwater flow systems and has a package that provides a link to the MODFLOW
codes. The MODFLOW-NWT and MT3DMS input packages used to create the groundwater flow
and transport model, and a brief description of their use, is provided in Table 1.
Appendix C

4 GROUNDWATER FLOW AND TRANSPORT MODEL CONSTRUCTION
The flow and transport model for the study was developed through a multi -step process. First, a 3-D
model of the site hydrostratigraphy was constructed based on historical site construction drawings
and field data. Next, the model domain was determined, from which a numerical was produced. Flow
parameters, assigned to the numerical grid, were adjusted during the steady-state flow model
calibration process. Once the steady-state flow model was calibrated, a transient transport
simulation for the selected COls was calibrated by adjusting transport parameters to best match the
current day conditions.
Three terrain surface models for Buck were created using geographic information systems (GIS)
software: 1) current existing surface, 2) pre -construction surface without ash and ash basin dikes,
and 3) pre -construction surface with dikes but without ash. An interpolation tool in ArcGIS 10.3
software was used to generate the terrain surfaces as raster datasets with 20-foot cells. Each
surface was created to cover the extent of the groundwater model domain.
4.1 Model Hydrostratigraphy
The model hydrostratigraphy was developed using historical site construction drawings and borehole
data to construct three-dimensional surfaces representing contacts between hydrostratigraphic units
with properties provided in HDR Tables 11-7 through 11-11.
1) Existing Ground Surface
Topographic and bathymetry elevation contours and spot elevations were produced from surveys
conducted in 2014. Since these surveys did not cover the entire model extent, elevation data
extracted as spot elevations from the North Carolina Floodplain Mapping Program's 2010 LiDAR
elevation data were used for the areas surrounding the surveys. At Buck, simplified elevation
contours were digitized along the river channels to depress the surface a small amount below water
level.
2) Pre -construction Surface
Elevation contours of the original ground surface were digitized in CAD from engineering drawings
supplied by Duke Energy. These data were imported into GIS, and georeferenced. These contours
were trimmed to the areas underlying ash basins, dams, and dikes and ash storage areas. The
source data used in the existing surface were then replaced by the original surface data where there
was overlap. Elevation data from coal storage areas were removed. The pre -construction surface
was then created using the combination of original surface elevations, 2014 survey elevations, and
2010 LiDAR elevations.
3) Pre -construction Surface with Dikes
Surface models of the ash basin dams and dikes were constructed from crest elevations as
determined from the 2014 survey and slopes given on the engineering drawings. Only the sections
of the dams and dikes facing the ash basins were modeled in this way. The 2014 survey data were
used for dike/dam crests and outwardly facing surfaces. These surfaces were merged with the pre -
construction surface. These GIS data sets were exported into formats readable by RockWorksTm and
GMS MODFLOW.
Appendix C

4) 3-D Hydrostratigraphic Grids
The natural materials in the CSA boreholes and existing boreholes were assigned a
hydrostratigraphic layer using the above classification scheme and judgment and the borehole data
entered into RockWorks 16TM for 3-D modeling. In the portions of the area to be modeled for which
borehole data is not available, dummy boreholes were used to extend the model to the model
boundaries. These boreholes were based on the hydrostratigraphic thickness of the existing
boreholes and the elevation of the existing boreholes based on the assumption that the
hydrostratigraphic layers are a subdued replica of the original topography of the site and geologic
judgment.
A grid of the pre -construction ground surface (described above) was used to constrain the modeling
of the natural layers. For gridding the data on a 20 ft x 20 ft grid across the area to be modeled,
hybrid algorithm was used with inverse distance weighted two (2) and triangulation weighted one (1)
and declustering, smoothing, and densifying subroutines. The declustering option is used to remove
duplicate points and de -cluster clustered points. The option creates a temporary grid with a z-value
assigned based on the closet data point to the midpoint of a voxel. The smoothing option averages
the z-values in a grid based on a filter size. For this modeling, the z-value is assigned the average of
itself and that of the eight nodes immediately surrounding it. One smoothing pass is made. The
densify option adds additional points to the xyz input by fitting a Delaunay triangulation network to
the data and adding the midpoint of each triangle to the xyz input points. The net result is that the
subsequent gridding process uses more control points and tends to constrain algorithms that may
become creative in areas of little control. Only one densification pass is made. The completed model
grids were exported in spreadsheet format for use in the groundwater flow and transport model.
4.2 GMS MODFLOW Version 10
The conceptual model approach to construct a MODFLOW simulation in GMS MODFLOW consists
of employing GIS tools in a map module to develop a conceptual model of the site being modeled.
The location of sources/sinks, layer parameters (such as hydraulic conductivity), and all other data
necessary for the simulation can be defined at the conceptual model level. Once this model is
complete, the grid is generated and the conceptual model is converted to the grid model and all of
the cell -by -cell assignments are performed automatically
The following table presents the sequence of the steps used for the groundwater modeling. Steps 1
through 6 describe the creation of 3-D MODFLOW model.
Step 1. Creating raster files for the model layer
- 3 surface layers (pre -construction, pre -construction with dike, and existing surface
including dike and ash) using GIS and AutoCad
- 2 subsurface layers (transition (TZ) and bedrock (BR)) by converting 3-D scatter data
Step 2. Creating the Raster Catalog to group the raster layers
- Assigning Horizons and materials for each layer
Step 3. Creating horizon surfaces (i.e. TIN) from raster data
- Used exiting surface and bedrock rasters
Appendix C

Step 4. Building Solids from the Raster Catalog and TINs
- Used raster data for the top and bottom elevations of the solids
Step 5. Creating the conceptual model
- Building model boundary, specified head boundary, and drain
- Defining zones and assigning hydraulic conductivity and recharge rate
- Importing observation wells and surface flow data
Step 6. Creating the MODFLOW 3-D grid model
- Converting the solids to 3-D grid model using boundary matching
- Mapping the conceptual model to 3-D MODFLOW grid
Step 7. Flow model calibration/Sensitivity Analysis
- Initializing the MODFLOW model
- Steady-state calibration with the trial -and -error method
- Parameters: hydraulic conductivity and recharge rate
- Used observation well and surface flow data
Step 8. Setting the transport model (MT3DMS)
- Species
- Stress periods
- Porosity and dispersion coefficient
- Distribution coefficient (Kd) from the lab experiments
- Recharge concentrations
Step 9. Performing model simulations
- Model scenarios - Existing Conditions, Cap -in -Place, and Excavation
4.3 Model Domain and Grid
The model domain encompasses the Buck site, including a section of the Yadkin River and all site
features relevant to the assessment of groundwater. The model domain extends beyond the ash
management areas to hydrologic boundaries such that groundwater flow and COI transport through
the area is accurately simulated without introducing artificial boundary effects.
The bounding rectangle around the model domain extends 8,900 feet north to south and 8,700 feet
east to west and has a grid consisting of 626,062 active cells in ten layers (Figures 1-3). In plan
view, the Buck model domain is bounded by the following hydrologic features of the site (Figure 4):
• the southern shore of the Yadkin River to the north,
• the drainage divide to the west between the Yadkin River and Long Ferry Road,
Appendix C 10

the drainage divide approximately defined by Long Ferry and Leonard Roads to the south,
and
the drainage feature, pond, and unnamed stream to the east between Leonard Road and the
Yadkin River.
Within the model domain, the unnamed stream and drainage feature to the west of the Primary Cell
acts as an internal boundary.
The domain boundary was developed by manually digitizing 2-foot LiDAR contours in ArcMap. The
lower limit of the model domain coincides with an assumed maximum depth of water yielding
fractures in bedrock. This was assumed to be 80 feet below the base of the TZ across the site upper
limit based on a review of boring logs contained in the CSA (HDR 2015).
There are a total of 10 model layers divided among the identified hydrostratigraphic units to simulate
flow with a vertical flow component (Figures 2 and 3). The units are represented by the model layers
listed below:
• Model layers 1 through 3
• Model layers 2 through 4
• Model layer 5
• Model layer 6
• Model layer 7
• Model layer 8
• Model layers 9 and 10
Ash Material
Dike and Ash Storage Material
M1 Saprolite and Alluvium where present
M1 Saprolite
M2 Saprolite
Transition Zone
Fractured Bedrock
4.4 Hydraulic Parameters
Horizontal and vertical hydraulic conductivities, which are specific for each hydrostratigraphic unit,
are the primary determinants of groundwater flow for a given configuration of boundary conditions
and sources and sinks, including recharge. Field measurements of these parameters from the CSA
(HDR Tables 11-7 through 11-11) provided guidance for their selection during the flow model
calibration.
4.5 Flow Model Boundary Conditions
Boundary conditions for the Buck flow model are one of two types: constant head or drain. No -flow
boundaries of the site have no prescribed boundary in the model. The outer boundary of the model
domain was selected to coincide with physical hydrologic boundaries at rivers and drainage features,
and no -flow boundaries at topographic divides (Figure 4).
External and internal drain boundaries were applied at the unnamed streams east and west of the
site and at selected low areas in the model interior to limit the rise of the modeled water table above
ground surface (Figure 4). At the unnamed tributaries, drain boundaries were applied with an
assumed conductance of 10 feet/day, an assumed bed thickness of one foot, and width equal to the
model cell width.
It is noted that constant head boundary conditions may not be valid if groundwater extraction is
considered as a corrective action alternative. In this case, the constant head boundary assumption
should be validated by a pump test or other means.
Appendix C 11

4.6 Flow Model Sources and Sinks
Recharge is the only source considered in the model. (Drainage boundaries are described above as
flow boundary conditions.) No pumping wells or other sources and sinks were explicitly identified in
the CSA (HDR 2015). The mean annual recharge in the Piedmont ranges from 4.0 to 9.7 inches per
year (Daniel 2001). The recharge applied in the model is shown in Figure 5.
4.7 Flow Model Calibration Targets
The steady-state flow model calibration targets are the 58 water level observations made in July
2015. These wells include 26 wells screened in the ash, the dikes, and shallow zone (S/M1/M2), 18
wells in the transition zone, and 14 wells fractured bedrock. Observations were assigned by layer as
shown in Table 3.
4.8 Transport Model Parameters
The calibrated, steady-state flow model was used to apply flow conditions for the transport models at
the Active Ash Basin Primary Cell, Ash Storage Area, and Secondary Cell (as shown in HDR CSA
Figures 2-2 and 2-4) where the highest concentrations were detected during the July 2015 sampling
event. The Primary and Secondary cells of the Active Ash Basin are also referred to as Cell 1
Additional Primary Cell and the Cell 3 Secondary Pond on selected figures from the CSA. Although
their approximate dates of operation are known, the sluiced ash loading histories for these locations
are not available. In order to develop a tool for predictive modeling at these locations, constant
concentration boundary conditions were applied at the water table at each location starting from the
date when the ash basin was placed in service. The relevant input parameters are the constant
concentration at the boundary as shown in Table 5. The linear sorption coefficient Kd applied for
sorptive constituents antimony, cobalt, and vanadium are 0.3 ml/g, 0.3 ml/g and 0.1 ml/g,
respectively. Preliminary results for sorption studies on soil samples obtained during the CSA at
Buck indicate that the approximate minimum Kd for vanadium in native soils beneath the ash basin
system is 110 ml/gram. Sorption is considered to be a calibration parameter as discussed in Section
5.3. A soil bulk density estimate of 2.12 grams/cubic centimeter for ash and 2.65 grams/cubic
centimeter for native soils were applied to the model.
The transport models for each COI were calibrated by adjusting the constant source concentration at
the water table above the target measured concentrations in adjacent wells (HDR Figures 10-9 and
10-13 through 10-15) after a 33-year simulation (1982-2015). The footprint of the source area was
limited by surrounding wells where the COI was non -detect. A comparison of the observed and
predicted concentrations of COls after model calibration is provided in Table 3.
Particle tracking was performed during model calibration to determine if advective travel times are
reasonable. Particles were placed at downgradient monitoring wells located nearest to the Yadkin
River and also near the southern model boundary. The particle tracks are shown in Figure 14 and
advective travel times are provided in Table 7.
Porosity is directly related to the flow velocity of COls through the subsurface. A single porosity
value of 0.20 was assigned to the ash, dike, and S/M1/M2 layers which is within the range of
estimated values from the CSA (HDR 2015). For the transition zone and fractured bedrock, the
porosities applied were 0.10 and 0.0005, respectively. Dispersivity quantifies the degree to which
mechanical dispersion of COls occurs in advecting groundwater. Dispersivity values of 80 feet, and
8 feet (longitudinal, transverse horizontal, transverse vertical) were applied in this model.
Traditionally, dispersivity is estimated to be some fraction of the scale, or plume length (Zheng and
Bennett [2002]). The commonly applied estimate is ten percent of the observation scale.
Appendix C 12

In order to avoid artificial oscillation in the numerical solution to the advection dispersion equation,
the grid Peclet number = (grid spacing/longitudinal dispersivity) should be less than two (Zheng and
Bennett [2002]). This implies that the maximum grid spacing in the principal direction of groundwater
flow should by less than 160 feet. The principal flow direction varies between vertical directly
beneath the COI source areas to horizontal outside the source areas.
4.9 Transport Model Boundary Conditions
The transport model boundary conditions have zero concentration where water leaves the model.
Initial concentrations, and concentrations in infiltrating recharge water, are zero. No background
concentration is specified. The active ash basin primary cell, ash storage area, and secondary cell
are represented by constant concentration boundary conditions.
4.10 Transport Model Sources and Sinks
The primary and secondary ash basin cells and the ash storage area are the sources for COls in the
model. Sources are modeled as a fixed concentration in the saturated ash layers of these areas
(Figure 5). The transport model sinks correspond to the constant head and drain boundaries of the
flow model. Water and COI mass are removed as they enter cells comprising these boundaries.
4.11 Transport Model Calibration Targets
The calibration targets are the measured arsenic and boron concentrations for July 2015 shown in
HDR Figures 10-9, 10-13 through 10-15, and 10-19 through 10-21. The specific target wells used for
model calibration are listed in Table 5
5 MODEL CALIBRATION TO CURRENT CONDITIONS
5.1 Flow Model Residual Analysis
The flow model was calibrated to the 58 water level observations taken during July 2015 in shallow,
deep, and bedrock wells. Water table elevation in the ash basin cells and selected depressions
across the site were also considered as part of the calibration. The locations of the observation wells
are provided in Figures 6 through 8. The trial -and -error calibration assumed homogeneous
conditions in each model layer. Beyond the ash basin cells, the model was most sensitive to
hydraulic conductivity of the upper, residual soil/saprolite layers (S/M1/M2) and TZ where the
elevation of the water table was inversely proportional to these parameters. The water table in the
ash basins was sensitive to hydraulic conductivity of the fill or dike. The flow model was also
sensitive to recharge.
Throughout the flow model calibration process, the assumption of a homogeneous transition zone
was retained, and its horizontal conductivity was assigned to give a reasonable, model result for the
water table and water level observations. Recharge was also fixed at reasonable values early in the
calibration process, and then refinements were made by adjusting hydraulic conductivity in the upper
layers (S/M1/M2) zonally as shown in Figure 9. The basis for delineating the zones in this way was
to obtain the best calibration locally using conductivity values within the range of measurements
made during the CSA.
Beyond the ash basin cells where groundwater flow is essentially horizontal, the model was
relatively insensitive to vertical hydraulic conductivity. Within the primary and secondary cells where
infiltration from recharge flows downward, the water table elevation was dependent on the vertical
hydraulic conductivity of the dike.
Appendix C 13

The calibrated flow model parameters are provided in Table 2. Measured and modeled water levels
(post -calibration) are compared in Table 3 and Figure 10. The calibrated flow model is considered to
represent steady-state flow conditions for the site and the ash basin system under a long-term,
average condition. The average root mean squared error (RMS) of the measured versus modeled
water levels for wells gauged in July 2015 is also provided in Table 3 for comparison with total
measured head change across the model domain. The model calibration goal is an RMS error less
than 10% of the change in head across the model domain. The ratio of the average RMS error to
total measured head change (the normalized root mean square error NRMSE), is 8.0 percent.
This NRMSE calculation omits two wells that appeared to have anomalous measured water levels
relative to the calibrated model. The residuals (measured head — modeled head) in wells AB-10S
and AB-91D were +21.0 ft, and -43 ft, respectively. Both of these wells are located in dikes where the
gradient of head is steep. Scaling and discretization of the model in combination with the elevation
change in the dikes may account for a significant portion of these residuals.
Contours of hydraulic heads for the calibrated flow model are shown in Figures 11 through 13.
Groundwater in the shallow aquifer, transition zone, and fractured bedrock flows radially from the
area centered on the primary cell discharge tower to the north, northeast, and northwest. Flow to
north discharges to the Yadkin River. Flows to the east and west discharge to the unnamed streams
and pond located there. Steeper hydraulic gradients in the shallow aquifer are associated with the
dikes west of the primary cell and east of the secondary cell. Groundwater flow from beneath the ash
basins is primarily vertical through the underlying dike and shallow aquifer. Groundwater flow
transitions to primarily horizontal flow at depths beneath the basins and beyond their lateral extent.
5.2 Flow Model Sensitivity Analysis
Sensitivity of the flow model was considered by varying selected parameters by 20 percent above
and below their respective calibration values and calculating the NRMSE for comparison with the
calibration value as shown in Table 3. Based on this approach, the flow model was most sensitive to
horizontal hydraulic conductivity of the shallow aquifer, followed by recharge to areas beyond the
ash basin cells, and hydraulic conductivity of the transition zone. The model is less sensitive to
vertical hydraulic conductivity beyond the ash basins, where the dominant flow direction is
horizontal. The elevation of the water table in the ash basin is particularly sensitive to recharge
although the effect on the site -wide NRMSE is limited.
5.3 Transport Model Calibration and Sensitivity
For transport model calibration, the constant source concentrations (resulting from contaminant flux
to groundwater from the ash basins and ash storage area sources) were adjusted to match the
concentrations in target wells as closely as possible. The constant source concentrations and Kd
were adjusted during transport model calibration. The transport model calibration results are shown
in Table 5.
Particle tracking was performed during model calibration to determine if advective travel times are
reasonable. Particles were placed at wells located near the Yadkin River and also in the ash basins.
The particle tracks are shown in Figure 14 and predicted advective travel times are provided in
Table 6.
Sensitivity analyses for sorption and porosity are provided in Tables 7 and 8. When the sorption
coefficient for arsenic was reduced by 50% from the calibration value, the modeled
concentrations increased as expected. Based on a comparison of AB-2S and AB-2SL,
sensitivity to Kd increases with distance from the constant source concentration. It is anticipated
Appendix C 14

that this effect is diminished away from the source area. Arsenic concentrations decreased
when porosity was increased from 0.2 to 0.3, although the magnitude of the increase was small.
This may be a consequence of the slow groundwater velocities in the underlying dike and
shallow aquifer beneath the Primary Cell.
P1
Boron concentrations also decreased when porosity was increased from 0.2 to 0.3. In general,
the magnitude of the decrease was greater beyond the area beneath the ash cells and storage
where groundwater velocities are higher.
6 PREDICTIVE SIMULATIONS OF CLOSURE SCENARIOS
The groundwater model, calibrated for flow and constituent fate and transport under existing
conditions, was applied to evaluate three closure scenarios at Buck: an Existing Conditions scenario;
the ash basins and ash storage areas Cap -in -Place scenario; and the Excavation scenario (ash
basins and ash storage areas removal). Being predictive, these simulations produce flow and
transport results for conditions that are beyond the range of those considered during the calibration.
Thus, the model should be recalibrated and verified over time as new data becomes available in
order to improve its accuracy and reduce its uncertainty. The model domain developed for existing
conditions was applied without modification for the Existing Conditions and Cap -in -Place scenarios.
For the Excavation scenario, the active ash basin primary cell, the active ash basin old primary cell,
the active ash basin secondary cell, and the ash storage areas were removed. The flow parameters
for this model were identical to the existing conditions models except for the removal of ash related
layers, and the same recharge rate being applied across the site.
6.1 Existing Conditions Scenario
The Existing Conditions scenario consists of modeling each COI using the calibrated model for
steady-state flow and transient transport under the existing conditions across the site until steady
state concentrations or a time period of 250 years are reached across the site and at the compliance
boundary. Active and inactive ash basin and ash storage areas are constant concentration sources
under this scenario. COI concentrations can only remain the same or increase initially for this
scenario with source concentrations being held at their constant value over all time. Thereafter, their
concentrations and discharge rates remain constant. This scenario represents the worst case in
terms of groundwater concentrations on and off site.
The time to achieve a steady state concentration plume depends on the source zone location
relative to the compliance boundary and its loading history. Source zones close to the compliance
will reach steady state sooner. The time to steady state concentration is also dependent on the
sorptive characteristics of each COI. Sorptive COls will be transient for a longer time period as their
peak breakthrough concentration travels at a rate that is less than the groundwater pore velocity.
Lower effective porosity will result in shorter times to achieve steady for both sorptive and non-
sorptive COIs. Lower total porosity will result in longer times for sorptive COIs.
Concentration contours and concentration breakthrough curves are all referenced to a time zero that
represents the time the closure action was implemented, which for the purpose of modeling is
assumed to be 2016. The scenario models COI concentrations forward from the end of the 58-year
simulation and represents 2015 as the initial concentrations. Constituent concentrations were
analyzed at six downgradient nested well sites. Monitor wells GWA-3S, GWA-3BRU, GWA-4S, and
GWA-41D, are located northeast of the active ash basin secondary cell towards the Yadkin River.
Appendix C 15

Monitor wells GWA-5S and GWA-5BRU are located north of the active ash basin secondary cell
towards the Yadkin River. Monitor wells GWA-12S and GWA-12BRU are located northeast of active
ash basin secondary cell and north of the active ash basin primary cell towards the Yadkin River.
Monitoring wells GWA-9S and GWA-9BR are located north of the active ash basin primary cell
towards the Yadkin River. Monitor well GWA-22D is located northwest of the active ash basin
primary cell towards the Yadkin River.
Figures 15 through 24 show predicted antimony concentrations versus time at representative
monitoring wells under all three scenarios. The concentration versus time curves show that under
the Existing Conditions scenario, antimony concentrations increase in all remaining wells from the
2015 conditions. Antimony concentrations do not achieve a steady-state in any well as
concentrations are still increasing by year 2265. Antimony concentrations are above the IMAC for
antimony, which is 1 pg/I, in 2015 in wells GWA-3S, GWA-5S, and GWA-5BRU and remain above
standard for antimony through 2265. Antimony concentrations increase above the IMAC standard by
year 2045 in wells GWA-41D, GWA-91D, GWA-22D and GWA-3BRU and by 2265 the concentration in
all wells exceeds the IMAC standard. Figures 74 through 76 show the predicted antimony
concentrations under this scenario in the shallow, deep, and fractured bedrock zones in 2015,
respectively. Figures 77 through 79 show the shallow, deep, and fractured bedrock zones in 2115.
All three groundwater zones show antimony greater than the IMAC standard of 1 pg/L at the
compliance boundary and at the Yadkin River. Antimony exits the model with groundwater
discharging at the Yadkin River to the north and east of the active ash basin secondary cell in all
groundwater zones. The highest concentrations of antimony leave the model north of the active ash
basin old primary cell.
Figures 25 through 31 show predicted boron concentrations versus time at representative monitoring
wells under all three model scenarios. The concentration versus time curves show that under the
Existing Conditions scenario, boron concentrations increase in all remaining wells from the 2015
conditions. Boron concentrations achieve a steady state in all wells by year 2147. Boron
concentrations are above the 2L Standard, which is 700 pg/l, in wells GWA-5S, GWA-91D, GWA-
22D, GWA-3BRU, GWA-5BRU and GWA-9BR and remain high through 2265 and boron
concentrations increase to above the 2L Standard by year 2019 in well GWA-3S. Figures 86 through
88 show the predicted boron concentrations under this scenario in the shallow, deep, and fractured
bedrock zones in 2015, respectively. Figures 89 through 91 show the shallow, deep, and fractured
bedrock zones in 2115. All three groundwater zones show boron greater than the 2L Standard of
700 pg/L at the compliance boundary and at the Yadkin River. Boron exits the model with
groundwater discharging at the Yadkin River to the north of the active ash basin primary cell and to
the north and east of the active ash basin secondary cell in all groundwater zones. The highest
concentrations of boron leave the model north of the active ash basin old primary cell.
Figures 32 through 38 show predicted chromium concentrations versus time at representative
monitoring wells under all three model scenarios. The concentration versus time curves show that
under the Existing Conditions scenario, chromium concentrations increase in all remaining wells
from the 2015 conditions. Chromium concentrations do not achieve a steady-state in any well as
concentrations are still increasing by year 2265. Chromium concentrations are above the 2L
Standard, which is 10 pg/I for chromium, in wells GWA-5S and GWA-5BRU in 2015 and remain
above the standard through 2265. By year 2115, chromium concentrations have increased above
the 2L Standard in wells GWA-3S, GWA-12S, GWA-3BRU and GWA-12BRU and by year 2235
chromium concentrations in well GWA-41D exceed the 2L Standard. Figures 98 through 100 show
Appendix C 16

the predicted chromium concentrations under this scenario in the shallow, deep, and fractured
bedrock zones in 2015, respectively. Figures 101 through 103 show the shallow, deep, and fractured
bedrock zones in 2115. All three groundwater zones show chromium greater than the 2L Standard
of 10 pg/L at the compliance boundary and at the Yadkin River. Chromium exits the model with
groundwater discharging at the Yadkin River to the north and east of the active ash basin secondary
cell in all groundwater zones. The highest concentrations of chromium leave the model north of the
active ash basin old primary cell.
Figures 39 through 49 show predicted cobalt concentrations versus time at representative
monitoring wells under all three model scenarios. The concentration versus time curves show that,
under the Existing Conditions scenario, cobalt concentrations increase in all remaining wells from
the 2015 conditions. Cobalt concentrations do not achieve a steady-state in any well as
concentrations are still increasing by year 2265. Cobalt concentrations in 2015 are above the IMAC
standard, which is 1 pg/I for cobalt, in wells GWA-3S, GWA-5S, GWA-41D, GWA-91D, GWA-3BRU
and GWA-5BRU and remain above the standard through2265. By year 2070, cobalt concentrations
have increased above the IMAC standard in wells GWA-4S and GWA-9S and by year 2265 cobalt
concentrations have exceeded the IMAC standard in all wells. Figures 110 through 112 show the
predicted cobalt concentrations under this scenario in the shallow, deep, and fractured bedrock
zones in 2015, respectively. Figures 113 through 115 show the shallow, deep, and fractured bedrock
zones in 2115. All three groundwater zones show cobalt greater than the IMAC standard of 1 pg/L at
the compliance boundary and at the Yadkin River. Cobalt exits the model with groundwater
discharging at the Yadkin River to the north of the active ash basin primary cell in the shallow and
deep zones and to the north and east of the active ash basin secondary cell in all groundwater
zones. The highest concentrations of cobalt leave the model north of the active ash basin old
primary cell.
Figures 50 through 57 show predicted hexavalent chromium concentrations versus time at
representative monitoring wells under all three model scenarios. The concentration versus time
curves show that, under the Existing Conditions scenario, hexavalent chromium concentrations
increase in all remaining wells from the 2015 conditions. Hexavalent chromium concentrations do
not achieve a steady-state in any well as concentrations are still increasing by year 2265.
Hexavalent chromium concentrations remain above DHHS standard, which is 0.07 pg/I, for in all
wells throughout the modeling period. Figures 122 through 124 show the predicted hexavalent
chromium concentrations under this scenario in the shallow, deep, and fractured bedrock zones in
2015, respectively. Figures 125 through 127 show the shallow, deep, and fractured bedrock zones in
2115. All three groundwater zones show hexavalent chromium greater than the 2L Standard of 0.07
pg/L at the compliance boundary and at the Yadkin River in year 2115. Hexavalent chromium exits
the model with groundwater discharging at the Yadkin River to the north and east of the active ash
basin secondary cell in all groundwater zones. The highest concentrations of hexavalent chromium
leave the model northeast of the active ash basin old primary cell.
Figures 58 through 61 show predicted sulfate concentrations versus time at representative
monitoring wells under all three model scenarios. The concentration versus time curves show that
under the Existing Conditions scenario, sulfate concentrations increase in the four remaining wells
from the 2015 conditions. Sulfate concentrations achieve a steady state in all wells by year 2141.
Sulfate concentrations remain above the 2L Standard, which is 250,000 pg/I for sulfate, in wells
GWA-41D and GWA-9BR till 2265 and sulfate concentrations increase above the 2L Standard by
year 2063 in well GWA-91D. Predicted sulfate concentrations will not exceed the 2L Standard in well
Appendix C 17

GWA-5BRU under the Existing Conditions scenario. Figures 134 through 136 show the predicted
sulfate concentrations under this scenario in the shallow, deep, and fractured bedrock zones in
2015, respectively. Figures 137 through 139 show the shallow, deep, and fractured bedrock zones in
2115. All three groundwater zones show sulfate greater than the 2L Standard of 250,000 pg/L at the
compliance boundary and at the Yadkin River. Sulfate exits the model with groundwater discharging
at the Yadkin River to the north of the active ash basin primary cell and to the north and east of the
active ash basin secondary cell in all groundwater zones. The highest concentrations of sulfate leave
the model north and east of the active ash basin old primary cell.
Figures 62 through 73 show predicted vanadium concentrations versus time at representative
monitoring wells under all three model scenarios. The predicted vanadium concentration in all wells
exceeds the IMAC for vanadium, which is 0.3 pg/I, in all scenarios. The concentration versus time
curves show that, under the Existing Conditions scenario, vanadium concentrations increase in all
wells from the 2015 conditions. Vanadium concentrations do not achieve a steady-state in any well
as concentrations are still increasing by year 2265. Vanadium concentrations are above the IMAC
standard for vanadium in wells GWA-3S, GWA-4S, GWA-5S, GWA-9S, GWA-41D, GWA-91D, GWA-
22D, GWA-3BRU, and GWA-5BRU in 2015 and remain above the standard through 2265. By year
2035, the vanadium concentration in wells GWA-12S, GWA-9BR, and GWA-12BRU will exceed the
IMAC standard. Figures 146 through 148 show the predicted vanadium concentrations under this
scenario in the shallow, deep, and fractured bedrock zones in 2015, respectively. Figures 149
through 151 show the shallow, deep, and fractured bedrock zones in 2115. All three groundwater
zones show vanadium greater than the IMAC standard of 0.3 pg/L at the compliance boundary and
at the Yadkin River. Vanadium exits the model with groundwater discharging at the Yadkin River to
the north and west of the active ash basin primary cell in the shallow, deep, and bedrock zones and
to the north and east of the active ash basin secondary cell in all groundwater zones. The highest
concentrations of vanadium leave the model north of the active ash basin primary cell.
6.2 Ash Basin Cap -in -Place Scenario
The Cap -in -Place model simulates the effects of covering the ash basins and ash storage areas, and
inactive ash basins at the beginning of this scenario. In the model, recharge and source zone
concentrations at the ash basins and ash storage areas are set to zero at the beginning of the
simulation. Groundwater flow is affected by this scenario as the water table is lowered and
groundwater velocities may be reduced beneath the covered areas. The water table within the active
ash basin primary cell is reduced by approximately 35 feet, and within the active ash basin old
primary and secondary cell is reduced by approximately 33 feet.
In the model, non sorptive COls will move downgradient at the pore velocity of groundwater and will
be displaced by the passage of a single pore water volume of clean water. Sorptive COI migration
will be retarded relative to the groundwater pore velocity as they are desorbed by clean water. The
model uses the predicted concentrations from the 2015 calibration as the starting concentrations for
the model scenario.
Figures 15 through 24 show predicted antimony concentrations versus time at representative
monitoring wells under all three scenarios. The concentration versus time curves show that under
the Cap -in -Place scenario, antimony concentrations increase in all remaining wells except GWA-3S
from the 2015 conditions. Of the initially increasing wells, only well GWA-3BRU has reached a peak
concentration and is decreasing by year 2115. Antimony concentrations in GWA-91D and GWA-22D
achieve a steady-state by year 2125. The remaining six initially increasing wells continue to increase
through 2265. Antimony concentrations remain above the IMAC standard in wells GWA-5S and
Appendix C 18

GWA-5BRU through 2265. Antimony concentrations increase above the IMAC standard by year
2025 in well GWA-41D, and 2190 in well GWA-4S. Concentrations in well GWA-3S begin the
scenario above the IMAC standard but decrease below the standard value in year 2019 and
continue decreasing through the modeling period. Antimony concentrations do not exceed the IMAC
standard under the Cap -in -Place scenario in wells, GWA-12S, GWA-91D, GWA-3BRU, or GWA-
12BRU. Figures 80 through 82 show the predicted antimony concentrations under this scenario in
the shallow, deep, and fractured bedrock zones in 2115. All three groundwater zones show antimony
greater than the IMAC standard of 1 pg/L at the compliance boundary and at the Yadkin River.
Antimony exits the model with groundwater discharging at the Yadkin River to the north and east of
the active ash basin secondary cell in all groundwater zones. The highest concentrations of
antimony leave the model north of the active ash basin old primary cell.
Figures 25 through 31 show predicted boron concentrations versus time at representative monitoring
wells under all three model scenarios. The concentration versus time curves show that under the
Cap -in -Place scenario, boron concentrations decrease in all remaining wells except for well GWA-
5BRU from the 2015 conditions. By year 2018 the concentrations in GWA-5BRU have peaked and
are decreasing. Boron concentrations do not achieve a steady state as concentrations are
decreasing in all wells in year 2265. Boron concentrations begin the scenario above the 2L Standard
in wells GWA-5S, GWA-91D, GWA-22D, GWA-3BRU, GWA-5BRU and GWA-9BR, but by year 2115
concentrations have decreased below the standard value in all wells except GWA-5S and GWA-
5BRU, and by year 2265 concentrations are below the 2L Standard in all wells. Figures 92 through
94 show the predicted boron concentrations under this scenario in the shallow, deep, and fractured
bedrock zones in 2115, respectively. All three groundwater zones show boron greater than the 2L
Standard of 700 pg/L at the compliance boundary and at the Yadkin River. Boron exits the model
with groundwater discharging at the Yadkin River to the north of the active ash basin primary cell
and to the north and east of the active ash basin secondary cell in all groundwater zones. The
highest concentrations of boron leave the model north of the active ash basin old primary cell.
Figures 32 through 38 show predicted chromium concentrations versus time at representative
monitoring wells under all three model scenarios. The concentration versus time curves show that
under the Cap -in -Place scenario, chromium concentrations increase from the 2015 conditions in all
remaining wells except GWA-3S and GWA-4D,. Concentrations in wells GWA-5S, GWA-12S, GWA-
3BRU, and GWA-5BRU reach peaks by years 2059, 2220, 2126, and 2180, respectively, after which
concentrations decrease through to year 2265. Concentrations in well GWA-41D decrease until year
2035, after which concentrations increase through to year 2265, and concentrations in GWA-12BRU
increase throughout the scenario time frame. Concentrations in well GWA-3S are decreasing at the
beginning and end of the scenario. Chromium concentrations do not achieve a steady-state in any
well by year 2265. Chromium concentrations remain above the 2L Standard for chromium in wells
GWA-5S and GWA-5BRU through 2265 and concentrations in GWA-12S and GWA-12BRU are
above the 2L Standard by year 2265. Concentrations in the remaining three wells are below the 2L
Standard throughout the scenario run. Figures 104 through 106 show the predicted chromium
concentrations under this scenario in the shallow, deep, and fractured bedrock zones in 2115,
respectively. All three groundwater zones show chromium greater than the 2L Standard of 10 pg/L at
the compliance boundary and at the Yadkin River. Chromium exits the model with groundwater
discharging at the Yadkin River to the north and east of the active ash basin secondary cell in all
groundwater zones. The highest concentrations of chromium leave the model north of the active ash
basin old primary cell.
Appendix C 19

Figures 39 through 49 show predicted cobalt concentrations versus time at representative
monitoring wells under all three model scenarios. The concentration versus time curves show that
under the Cap -in -Place scenario, cobalt concentrations increase in all remaining wells except for
GWA-3S, GWA-41D, and GWA-3BRU from the 2015 conditions. Cobalt concentrations in wells GWA-
4S, GWA-12S, GWA-5BRU and GWA-12BRU continue to increase throughout the scenario time
frame while concentrations in well GWA-3S decrease throughout the time frame. After initially
decreasing, cobalt concentrations in well GWA-41D begins to increase by year 2029 and continues to
increase to year 2265. After initially increasing, cobalt concentrations in wells, GWA-5S, GWA-91D,
GWA-22D, and GWA-3BRU, are all decreasing by year 2143. Cobalt concentrations do not achieve
a steady-state in any well by year 2265. Cobalt concentrations remain above the IMAC standard for
cobalt in wells GWA-5S, GWA-41D, GWA-91D, GWA-22D, and GWA-5BRU till 2265. By year 2115,
cobalt concentrations have increased above the IMAC standard in wells GWA-4S and GWA-9S.
Cobalt concentrations in wells GWA-3S and GWA-3BRU are initially above the IMAC standard, but
by 2027 and 2053, respectively, concentrations have decreased below the IMAC standard and
remain below through year 2265. Cobalt concentrations in wells GWA-12S and GWA-12BRU do not
exceed the IMAC standard under the Cap -in -Place scenario conditions. Figures 116 through 118
show the predicted cobalt concentrations under this scenario in the shallow, deep, and fractured
bedrock zones in 2115, respectively. All three groundwater zones show cobalt greater than the
IMAC standard of 1 tag/L at the compliance boundary and at the Yadkin River. Cobalt exits the model
with groundwater discharging at the Yadkin River to the north of the active ash basin primary cell in
the shallow and deep zones and to the north and east of the active ash basin secondary cell in all
groundwater zones. The highest concentrations of cobalt leave the model north of the active ash
basin old primary cell.
Figures 50 through 57 show predicted hexavalent chromium concentrations versus time at
representative monitoring wells under all three model scenarios. The concentration versus time
curves show that under the Cap -in -Place scenario, hexavalent chromium concentrations increase in
all remaining wells except for GWA-3S, from the 2015 conditions, but the concentration in all wells is
increasing by year 2265. Hexavalent chromium concentrations do not achieve a steady-state in any
well as concentrations are still increasing by year 2265. Hexavalent chromium concentrations remain
above DHHS standard for hexavalent chromium in wells GWA-3S, GWA-5S, GWA-41D, and GWA-
5BRU till 2265. By year 2115, hexavalent chromium concentrations have increased above the DHHS
standard in wells GWA-4S, GWA-22D, and GWA-3BRU, and by year 2190 the concentration in
GWA-91D exceeds the DHHS standard. Figures 128 through 130 show the predicted hexavalent
chromium concentrations under this scenario in the shallow, deep, and fractured bedrock zones in
2115, respectively. All three groundwater zones show hexavalent chromium greater than the 2L
Standard of 0.07 tag/L at the compliance boundary and at the Yadkin River in year 2115. Hexavalent
chromium exits the model with groundwater discharging at the Yadkin River to the north and east of
the active ash basin secondary cell in all groundwater zones. The highest concentrations of
hexavalent chromium leave the model northeast of the active ash basin old primary cell.
Figures 58 through 61 show predicted sulfate concentrations versus time at representative
monitoring wells under all three model scenarios. The concentration versus time curves show that
under the Cap -in -Place scenario, sulfate concentrations increase in wells GWA-41D and GWA-5BRU
from the 2015 conditions. However, by year 2053, sulfate concentrations are decreasing in all four
wells. Sulfate concentrations do not achieve a steady state at the well locations as concentrations in
all four are decreasing in year 2265. Sulfate concentrations are initially above the 2L Standard in
wells GWA-41D and GWA-9BR, but by year 2040 and 2018, respectively, concentrations in these
Appendix C 20

wells are below the 2L Standard. Sulfate concentrations in well GWA-5BRU peak above the 2L
Standard between years 2041 and 2069, but are below the 2L Standard from year 2070 to
2265.Sulfate concentrations in well GWA-91D no not exceed the 2L Standard under the Cap -in -Place
scenario conditions. Figures 140 through 142 show the predicted sulfate concentrations under this
scenario in the shallow, deep, and fractured bedrock zones in 2115, respectively. All three
groundwater zones show sulfate less than the 2L Standard of 250,000 pg/L at the compliance
boundary and at the Yadkin River.
Figures 62 through 73 show predicted vanadium concentrations versus time at representative
monitoring wells under all three model scenarios. The predicted vanadium concentration in all wells
exceeds the IMAC for vanadium, which is 0.3 tag/I, in all scenarios. The concentration versus time
curves show that under the Cap -in -Place scenario, vanadium concentrations increase in all wells
except GWA-3S, GWA-5S, and GWA-3BRU, from the 2015 conditions. Vanadium concentrations in
well GWA-5S begin to increase after year 2046, while concentrations in wells GWA-3S and GWA-
3BRU continues to decrease throughout the scenario time frame with concentrations decreasing
below the IMAC standard by years 2170 and 2205, respectively. Vanadium concentrations do not
achieve a steady-state in any well by year 2265. Vanadium concentrations remain above the IMAC
standard for vanadium in wells GWA-4S, GWA-5S, GWA-9S, GWA-41D, GWA-91D, GWA-221D, and
GWA-5BRU till 2265. By year 2051, the vanadium concentration in wells GWA-9BR, and GWA-
12BRU will exceed the IMAC standard. Vanadium concentrations in well GWA-12S no not exceed
the IMAC standard under the Cap -in -Place scenario conditions. Figures 152 through 154 show the
predicted vanadium concentrations under this scenario in the shallow, deep, and fractured bedrock
zones in 2115, respectively. All three groundwater zones show vanadium greater than the IMAC
standard of 0.3 pg/L at the compliance boundary and at the Yadkin River. Vanadium exits the model
with groundwater discharging at the Yadkin River to the north and west of the active ash basin
primary cell in the shallow, deep, and bedrock zones and to the north and east of the active ash
basin secondary cell in all groundwater zones. The highest concentrations of vanadium leave the
model north of the active ash basin primary cell.
6.3 Excavation Scenario
The Excavation Scenario models simulate the effects of removing the active ash basins and ash
storage areas at the beginning of this scenario. In the model, source zone concentrations at the ash
basins and ash storage areas are set to zero while recharge is applied at the same rate as other
surrounding areas. Groundwater flow beneath the ash basin is affected by this scenario as the
basins are completely drained and the source of COls is removed. In the model, non-sorptive COls
will move downgradient at the pore velocity of groundwater. Sorptive COI migration will be retarded
relative to the groundwater pore velocity as they are desorbed by clean water. The model uses the
predicted concentration from the 2015 calibration as the starting concentration for this model
scenario.
Figures 15 through 24 show predicted antimony concentrations versus time at representative
monitoring wells under all three scenarios. The concentration versus time curves show that under
the Excavation scenario, antimony concentrations initially increase in all remaining wells except for
well GWA-3S, from the 2015 conditions. Concentrations in GWA-3S initially decrease, begin to
increase in year 2028, peak in years 2119, then continue to decrease to year 2265. By year 2081,
antimony concentrations in well GWA-5S begin to decrease and by year 2265 concentration in wells
GWA-91D, GWA-221D, and GWA-3BRU are decreasing. Antimony concentrations in wells GWA-4S,
GWA-12S, GWA-5BRU, and GWA-12BRU continue to increase throughout the scenario time frame.
Appendix C 21

Antimony concentrations do not achieve a steady-state in any well. Antimony concentrations remain
above the IMAC standard in wells GWA-3S, GWA-5S and GWA-5BRU till 2265. Antimony
concentrations increase above the IMAC standard by year 2115 in wells GWA-41D, GWA-91D, GWA-
22D, and GWA-3BRU, and by 2265 the concentration in well GWA-4S exceeds the IMAC standard.
Antimony concentrations do not exceed the IMAC standard under the Excavation scenario in wells,
GWA-12S or GWA-12BRU. Figures 83 through 85 show the predicted antimony concentrations
under this scenario in the shallow, deep, and fractured bedrock zones in 2115. All three groundwater
zones show antimony greater than the IMAC standard of 1 pg/L at the compliance boundary and at
the Yadkin River. Antimony exits the model with groundwater discharging at the Yadkin River to the
north and east of the active ash basin secondary cell in all groundwater zones. The highest
concentrations of antimony leave the model north of the active ash basin old primary cell.
Figures 25 through 31 show predicted boron concentrations versus time at representative monitoring
wells under all three model scenarios. The concentration versus time curves show that under the
Excavation scenario, boron concentrations decrease in all remaining wells except for wells GWA-91D,
GWA-22D, and GWA-5BRU, from the 2015 conditions. By years 2031, 2037, and 2017, boron
concentrations in wells GWA-91D, GWA-22D, and GWA-5BRU, respectively, have peaked after
which concentrations decrease to year 2265. Boron concentrations do not achieve a steady state as
concentrations are decreasing in all wells in year 2265. Boron concentrations begin the scenario
above the 2L Standard in wells GWA-5S, GWA-91D, GWA-22D, GWA-3BRU, GWA-5BRU and GWA-
9BR, but by year 2098 concentrations have decreased below the standard value in all wells. Boron
concentrations in well GWA-3S do not exceed the 2L Standard under the Excavation scenario
conditions. Figures 95 through 97 show the predicted boron concentrations under this scenario in
the shallow, deep, and fractured bedrock zones in 2115, respectively. All three groundwater zones
show boron less than the 2L Standard of 700 pg/L at the compliance boundary and at the Yadkin
River.
Figures 32 through 38 show predicted chromium concentrations versus time at representative
monitoring wells under all three model scenarios. The concentration versus time curves show that
under the Excavation scenario, chromium concentrations increase in all remaining wells from the
2015 conditions. Only in well GWA-41D do concentrations continue to rise throughout the scenario
time frame. Concentrations in wells GWA-5S, GWA-5BRU, GWA-3S, and GWA-3BRU begin to
decrease in years 2057, 2126, 2131 and 22160, respectively, and by year 2265 concentrations are
decreasing in wells GWA-12S and GWA-12BRU. Chromium concentrations do not achieve a steady-
state in any well by year 2265. Chromium concentrations remain above the 2L Standard for
chromium, in wells GWA-5S and GWA-5BRU till 2265 and concentrations in all wells except for
GWA-41D are above the 2L Standard by year 2083. Concentrations in well GWA-41D no not exceed
the 2L Standard under the Excavation scenario conditions. Figures 107 through 109 show the
predicted chromium concentrations under this scenario in the shallow, deep, and fractured bedrock
zones in 2115, respectively. All three groundwater zones show chromium greater than the 2L
Standard of 10 pg/L at the compliance boundary and at the Yadkin River. Chromium exits the model
with groundwater discharging at the Yadkin River to the north and east of the active ash basin
secondary cell in all groundwater zones. The highest concentrations of chromium leave the model
north of the active ash basin old primary cell.
Figures 39 through 49 show predicted cobalt concentrations versus time at representative
monitoring wells under all three model scenarios. The concentration versus time curves show that
under the Excavation scenario, cobalt concentrations increase in all remaining wells except for
Appendix C 22

GWA-3S from the 2015 conditions. Cobalt concentrations in wells GWA-3S and GWA-9S begin to
increase by years 2205 and 2026, respectively, and along with concentrations in wells GWA-4S and
GWA-12S continue to increase to year 2265. After initially increasing, concentrations in wells GWA-
5S, GWA-41D, GWA-91D, and GWA-22D decrease through to year 2265 beginning in years, 2063,
2148, 2140, 2126, and 2157 respectively. After initially increasing, concentrations in well GWA-
3BRU begins to decrease in year 2032 only to start increasing again by year 2245. Cobalt
concentrations do not achieve a steady-state in any well by year 2265. Cobalt concentrations remain
above the IMAC standard for cobalt in wells GWA-5S, GWA-41D, GWA-91D, GWA-22D, and GWA-
5BRU till 2265. By year 2085, cobalt concentrations have increased above the IMAC standard in
wells GWA-4S and GWA-9S. Cobalt concentrations in wells GWA-3S and GWA-3BRU are initially
above the IMAC standard, but by 2125 and 2175, respectively, concentrations have decreased
below the IMAC standard and remain below through year 2265. Cobalt concentrations in wells
GWA-12S and GWA-12BRU do not exceed the IMAC standard under the Excavation scenario
conditions. Figures 119 through 121 show the predicted cobalt concentrations under this scenario in
the shallow, deep, and fractured bedrock zones in 2115, respectively. All three groundwater zones
show cobalt greater than the IMAC standard of 1 pg/L at the compliance boundary and at the Yadkin
River. Cobalt exits the model with groundwater discharging at the Yadkin River to the north of the
active ash basin primary cell in the shallow and deep zones and to the north and east of the active
ash basin secondary cell in all groundwater zones. The highest concentrations of cobalt leave the
model north of the active ash basin old primary cell.
Figures 50 through 57 show predicted hexavalent chromium concentrations versus time at
representative monitoring wells under all three model scenarios. The concentration versus time
curves show that under the Excavation scenario, hexavalent chromium concentrations increase in all
remaining wells from the 2015 conditions, and continue to increase throughout the scenario time
frame. Hexavalent chromium concentrations do not achieve a steady-state in any well as
concentrations are still increasing by year 2265. Hexavalent chromium concentrations remain above
DHHS standard for hexavalent chromium in wells GWA-3S, GWA-5S, GWA-41D, and GWA-5BRU till
2265. By year 2074, hexavalent chromium concentrations have increased above the DHHS standard
in wells GWA-4S, GWA-91D, GWA-22D, and GWA-3BRU. Figures 131 through 133 show the
predicted hexavalent chromium concentrations under this scenario in the shallow, deep, and
fractured bedrock zones in 2115, respectively. All three groundwater zones show hexavalent
chromium greater than the 2L Standard of 0.07 Ng/L at the compliance boundary and at the Yadkin
River in year 2115. Hexavalent chromium exits the model with groundwater discharging at the
Yadkin River to the north and east of the active ash basin secondary cell in all groundwater zones.
The highest concentrations of hexavalent chromium leave the model northeast of the active ash
basin old primary cell.
Figures 58 through 61 show predicted sulfate concentrations versus time at representative
monitoring wells under all three model scenarios. The concentration versus time curves show that
under the Excavation scenario, sulfate concentrations increase in wells GWA-41D, GWA-91D, and
GWA-5BRU from the 2015 conditions. However, by year 2033, sulfate concentrations are
decreasing in all four wells. Sulfate concentrations do not achieve a steady state at the well locations
as concentrations in all four are decreasing in year 2265. Sulfate concentrations are initially above
the 2L Standard in wells GWA-41D and GWA-9BR, but by year 2037 and 2019, respectively,
concentrations in these wells are below the 2L Standard. Sulfate concentrations in wells GWA-91D
and GWA-5BRU no not exceed the 2L Standard under the Excavation scenario conditions. Figures
143 through 145 show the predicted sulfate concentrations under this scenario in the shallow, deep,
Appendix C 23

and fractured bedrock zones in 2115, respectively. All three groundwater zones show sulfate less
than the 2L Standard of 250,000 pg/L at the compliance boundary and at the Yadkin River.
Figures 62 through 73 show predicted vanadium concentrations versus time at representative
monitoring wells under all three model scenarios. The predicted vanadium concentration in all wells
exceeds the IMAC for vanadium, which is 0.3 pg/l, in all scenarios. The concentration versus time
curves show that under the Excavation scenario, vanadium concentrations increase in all wells
except GWA-3S from the 2015 conditions. Concentrations in GWA-3S decrease throughout the
scenario time frame. Conversely, concentrations in well GWA-9BR increase throughout the scenario
time frame. After initially increasing, vanadium concentrations in the remaining ten wells are all
decreasing by year 2175. Vanadium concentrations do not achieve a steady-state in any well by
year 2265. Vanadium concentrations remain above the IMAC standard for vanadium in wells GWA-
3S, GWA-4S, GWA-5S, GWA-9S, GWA-41D, GWA-91D, GWA-22D,GWA-3BRU and GWA-5BRU till
2265. By year 2038, the vanadium concentration in wells GWA-12S, GWA-9BR, and GWA-12BRU
will exceed the IMAC standard. Figures 155 through 157 show the predicted vanadium
concentrations under this scenario in the shallow, deep, and fractured bedrock zones in 2115,
respectively. All three groundwater zones show vanadium greater than the IMAC standard of 0.3
pg/L at the compliance boundary and at the Yadkin River. Vanadium exits the model with
groundwater discharging at the Yadkin River to the north and west of the active ash basin primary
cell in the shallow, deep, and bedrock zones and to the north and east of the active ash basin
secondary cell in all groundwater zones. The highest concentrations of vanadium leave the model
north of the active ash basin primary cell.
7 SUMMARY AND CONCLUSIONS
7.1 Model Assumptions and Limitations
The model assumptions and limitations include the following:
• The steady-state flow model was calibrated to hydraulic heads measured at observation
wells in July 2015 and considered the ash basin water level. The model is not calibrated to
transient water levels over time, recharge or river flow. A steady-state calibration does not
consider groundwater storage and does not calibrate the groundwater flux into adjacent
surface water bodies.
• MOFLOW simulates flow through porous media and groundwater flow in the bedrock
groundwater zone is via fractures in the bedrock. A single domain MODFLOW modeling
approach for simulating flow in the primary porous groundwater zones and bedrock was
used for contaminant transport at the Buck site.
• The model was calibrated by adjusting the constant source concentrations at the ash basins
and ash storage areas to reasonably match 2015 COI concentrations in groundwater.
• For the purposes of numerical modeling and comparing closure scenarios, it is assumed that
the selected closure scenario will be completed in 2015.
• Predictive simulations were performed and steady-state flow conditions were assumed from
the time that the ash basins and ash storage area were placed in service through the current
time until the end of the predictive simulations (2265).
Appendix C 24

• COI source zone concentrations at the inactive and active ash basins and ash storage area
were applied uniformly within each source area and assumed to be constant with respect to
time for transport model calibration.
• The uncertainty in model parameters and predictions has not been quantified; therefore the
error in the model predictions is not known. It is assumed the model results are suitable for a
relative comparison of closure scenario options.
• Since the Yadkin River is modeled as a constant head boundary in the numerical model, it
will not be possible to assess the affects of pumping wells or other groundwater sinks that
are near the river.
• The model does not account for varying geochemical conditions such as pH and redox
potential that could affect COI mobility and change modeling results. Site -specific
geochemistry and geochemical modeling will be considered in CAP2.
7.2 Model Predictions
The model predictions are summarized as follows:
For the Existing Conditions scenario, the model predicts that none of the seven simulated
constituents are in steady-state with respect to transport in 2015, but that the concentration
of all constituents exceed the 2L, IMAC, or DHHS standard at the compliance boundary and
the concentration of all constituents exceed the 2L, IMAC, or DHHS standard at the Yadkin
River boundary. By 2115, concentrations of all constituent are still increasing in the model
domain and the concentrations of all constituents exceed the 2L, IMAC, or DHHS standard at
the compliance boundary. Boron and sulfate concentrations reach steady-state by 2165 and
2155, respectively.
• For the Cap -in -Place scenario, model predictions show that in 2115, antimony, boron, cobalt,
vanadium, and chromium will exceed the 2L or IMAC standard at the compliance boundary
and at the Yadkin River. Sulfate concentrations will be below the 2L Standard at the
compliance boundary and at the Yadkin River. Hexavalent chromium concentrations, which
did not begin the scenario in exceedance of the DHHS standard at the Yadkin River, will
exceed the DHHS standard at the compliance boundary and at the Yadkin River. Overall, the
concentrations of all seven constituents will exceed the 2L, IMAC, or DHHS standards within
the model domain and none will reach steady-state with respect to transport for the entire
modeling period from 2015-2265.
• For the Excavation scenario, model predictions show that in 2115, antimony, cobalt,
vanadium, and chromium will exceed the 2L or IMAC standard at the compliance boundary
and at the Yadkin River. Sulfate and boron concentrations will be below the 2L Standard at
the compliance boundary and at the Yadkin River. Hexavalent chromium concentrations,
which did not begin the scenario in exceedance of the DHHS standard at the Yadkin River,
will exceed the DHHS standard at the compliance boundary and at the Yadkin River. Overall,
the concentrations of all constituents, except boron and sulfate, will exceed the 2L, IMAC, or
DHHS standards within the model domain and none of the seven will reach steady-state with
respect to transport for the entire modeling period from 2015-2265. Boron and sulfate
concentrations within the model domain will decrease below the 2L Standard by 2135 and
2105, respectively.
Appendix C 25

8 REFERENCES
Daniel, C.C., III, 2001, Estimating ground -water recharge in the North Carolina Piedmont for land
use planning [abs.], in 2001 Abstracts with Programs, 50th Annual Meeting, Southeastern
Section, April 5-6, 2001: Raleigh, N.C., The Geological Society of America, v. 33, no. 2, p. A-
80.
Haven, W.T. Introduction to the North Carolina Groundwater Recharge Map -Groundwater Circular
Number 19, North Carolina Department of Environment and Natural Resources Division of
Water Quality, Groundwater Section.
HDR. Comprehensive Site Assessment Report, Buck Steam Station Ash Basin, August 2015.
LeGrand, H. E. 2004. A Master Conceptual Model for Hydrogeological Site Characterization in the
Piedmont and Mountain Region of North Carolina, A Guidance Manual, North Carolina
Department of Environment and Natural Resources Division of Water Quality, Groundwater
Section.
Niswonger, R.G., Panday, S., and Ibaraki, M. 2011. MODFLOW-NWT, A Newton formulation for
MODFLOW-2005: U.S. Geological Survey Techniques and Methods 6-A37, 44 p.
Zheng, C. and Bennett, G. Applied Contaminant Transport Modeling Second Edition, Wiley
Interscience, 2002.
Zheng, C. and P. Wang. 1999. MT3DMS, A modular three-dimensional multi -species transport
model for simulation of advection, dispersion and chemical reactions of contaminants in
groundwater systems, Documentation and Users Guide, U.S. Army Engineer Research and
Development Center Contract Report SERDP-99-1, Vicksburg, MS, 202 p.
Appendix C 26

Tables
Table 1. Description of MODFLOW and MT3DMS Input Packages Utilizedm
Table 2. Hydraulic Conductivity in ModelM
Table 3. Observed vs. Predicted Hydraulic Head (ft msl)M
Table 4. Effective Porosity in ModelM
Table 5. Transport Model Calibration ResultsM
Table 6. MODPATH Advective Travel Time Results0
Table 7. Arsenic Transport Parameter Sensitivity AnalysisM.
Table 8. Boron Transport Parameter Sensitivity Analysis0

Table 1. Description of MODFLOW and MT3DMS Input Packages Utilized
MODFLOW Input Package
Description
Name (NAM)
Contains the names of the input and output files used in the
model simulation and controls the active model program
Basic (BAS)
Specifies input packages used, model discretization, number of
model stress periods, initial heads and active cells
Contains finite -difference grid information, including the number
Discretization (DIS)
and spacing of rows and columns, number of layers in the grid,
top and bottom model layer elevations and number of stress
periods
Specified Head and
Specifies a head and/or a concentration that remains constant
Concentration (CHD)
throughout the simulation
Drain (DRN)
Acts as a "drain" to remove water from the groundwater system.
Simulates drainage areas within the model
Recharge (RCH)
Simulates areal distribution of recharge to the
groundwater system
Newton Solver (NWT)
Contains input values and the Newton and matrix
solver options
Upstream Weighting (UPW)
Replaces the LPF and/or BCF packages and contains the input
required for internal flow calculations
Flow Transfer Link File (LMT)
Used by MTDMS to obtain the location, type, and flow rates of
all sources and sinks simulated in the flow model
MT3DMS Input Package
Description
Flow Transfer Link File (FTL)
Reads the LMT file produced by MODFLOW
Basic Transport Package (BTN)
Reads the MODFLOW data used for transport simulations and
contains transport options and parameters
Advection (ADV)
Reads and solves the selected advection term
Dispersion (DSP)
Reads and solves the dispersion using the explicit finite -
difference formulation
Source and Sink Mixing (SSM)
Reads and solves the concentration change due to sink/source
mixing using the explicit finite -difference formulation
Chemical Reaction (RCT)
Reads and solves the concentration change due to chemical
reactions using the explicit finite -difference formulation
Generalized Conjugate Gradient
T!olve7sthe matrix equations resulting from the implicit solution of
(GCG) Solver
the transport equation

Table 2. Hydraulic Conductivity in Model
Measured Value
Calibrated Model Value
Range'
Model
Hydrostratigraphic
Horizontal
Horizontal Hydraulic
Vertical Hydraulic
Layers
Unit
Hydraulic
Conductivity
Conductivity
Conductivity
Conductivity
(feet/day)
(feet/day)
feet da
1 - 3
Ash
3.45
0.341
0.341
2-4
Dike
---
0.0028
0.0028
S-1
11.366
1.1366
S-2
0.1137
0.0114
5-6
M1-Saprolite
0.72
S-3
2.557
0.2557
7
M2-Saprolite
0.35
S-4
0.0284
0.0057
S-5
0.1421
0.01421
S-6
0.1137
0.01137
8
TZ
0.98
2.842
0.5683
9 — 10
BR
0.025
0.025
0.02501
'Range = geometric mean +/- one standard deviation (see HDR Tables 11-7 to 11-11)

Table 3. Observed vs. Predicted Hydraulic Head (ft msl)
Well Name
Model Layer
Obs. Head
ft msl
Pred. Head
ft msl
Square Error
S.E. ft2
AB-10D
8
662.24
657.31
24.3
AB-1 D
8
691.78
676.45
234.96
AB-213R
10
697.04
689.93
50.49
AB-2D
8
697.01
690.25
45.64
AB-2S
6
697.78
694.34
11.84
AB-2SL
7
698.05
691.99
36.74
AB-3D
8
698.1
695.99
4.45
AB-3S
6
698.4
700.07
2.79
AB-4BR
10
679.71
683.5
14.38
AB-4BRU
9
680.83
684.1
10.71
AB-4S
6
680.9
686.14
27.51
AB-4SL
7
680.01
684.89
23.78
AB-5S
6
674.35
677.57
10.37
AB-5SL
7
674.37
674.31
0
AB-6BRU
9
673.6
663.97
92.66
AB-7BRU
9
666.75
663.87
8.27
AB-7S
6
672.99
664.12
78.7
AB-7SL
7
672.88
664
78.92
AB-8D
8
672.99
669.99
8.99
AB-8S
6
672.58
671.94
0.42
AB-9BR
10
654.11
653.51
0.35
AB-9S
6
667.23
657.5
94.72
AS-1 D
8
693.17
692.13
1.09
AS-1 S
6
693.52
698.92
29.16
AS-2D
8
693.83
700.38
42.92
AS-3D
8
696.94
703.52
43.32
AS-3S
6
696.11
710.43
205.12
BG-1 D
8
701.23
696.93
18.45
BG-1 S
6
704.16
699.3
23.62
BG-2D
8
703.65
703.19
0.21
BG-2S
6
703.69
706.06
5.61
BG-3S
6
687.81
703.18
236.25
GWA-10D
8
651.23
652.48
1.57
GWA-10S
6
649.84
652.23
5.69
GWA-11 D
8
671.69
667.04
21.65
GWA-11 S
6
672.5
666.87
31.74
GWA-12BRU
9
626.67
631.49
23.28
GWA-12S
6
626.53
631.74
27.15
GWA-1 D
8
699.9
708
65.68

Table 3. Observed vs. Predicted Hydraulic Head (ft msl)(cont.)
Well Name
Model Layer
Obs. Head
ft msl
Pred. Head
ft msl
Square Error
S.E. ft2
GWA-1 S
6
698.44
708.06
92.49
GWA-22D
8
630.71
634.18
12.03
GWA-2BR
10
677.11
679.41
5.27
GWA-2BRU
9
677.99
679.35
1.86
GWA-313RU
9
626.74
633.57
46.68
GWA-3S
6
624.65
632.84
67
GWA-4D
8
638.7
629.97
76.15
GWA-4S
6
642.38
632.69
93.94
GWA-5BRU
9
630.44
627.67
7.66
GWA-5S
6
625.17
627.59
5.84
GWA-6BR
10
645.54
642.19
11.19
GWA-613RU
9
645.31
641.85
11.98
GWA-6S
6
645.13
642.94
4.8
GWA-7D
8
647.53
650.86
11.08
GWA-7S
6
647.52
650.9
11.41
GWA-8D
8
685.52
666.62
357.16
GWA-9BR
10
663.53
656.58
48.35
GWA-9D
8
664.94
656.65
68.67
GWA-9S
6
666.89
659.8
50.3
Maximum 704.16 Sum S.E. 2,627.36 ft
Minimum 624.65 Avg S.E. 45.29 ft2
Max - Min 79.51 Sgrt (Avg S.E) 6.73 ft
0.08
NRMSE 8.0%

Table 4. Effective Porosity in Model
Model
Hydrogeologic
Effective Porosity
Layer
Unit
1 - 3
Ash Material
0.1
4-6
Dike and Ash Storage
0.1
Material
5
M1 — Saprolite
0.1
and Alluvium
6
M1 — Saprolite
0.1
and Alluvium
7
M2 - Saprolite
0.1
8
Transition Zone
0.05
9 — 10
Bedrock
0.005

Table 5. Transport Model Calibration Results
COI
Monitoring Well
Measured Concentration
(Ng/L)
Predicted Concentration
(Ng/L)
Ash Basin Primary Cell/Ash Storage Constant Source Concentration = 18 - 40 pg/L
Ash Basin Secondary Cell Constant Source Concentration = 5 - 2,000 Ng/L
AB-2BR
1.3
0.0
Antimony
AB-2S
22.5
22.3
AB-2SL
2.5
16.4
AB-3S
8.9
8.8
AB-4BR
5.1
0.2
AB-4SL
1.4
5.3
AB-5SL
1.9
3.4
AB-6BRU
6.3
8.4
AB-7BRU
1.8
2.9
AB-7SL
9.3
14.1
AB-8S
3.3
4.1
AB-9BR
1.6
1.4
AS-2 D
1.9
3.0
GWA-2BR
19.3
0.0
GWA-3S
2.1
1.4
GWA-71D
1.6
0.1
Ash Basin Primary Cell/Ash Storage Constant Source Concentration = 300 - 10,000 pg/L
Ash Basin Secondary Cell Constant Source Concentration = 300 - 15,000 pg/L
AB-1 OD
1,900
2,260
AB-1 D
1,500
1,760
AB-2S
1,800
2,180
AB-2SL
3,200
3,120
AB-3S
2,600
2,575
AB-4S
110
2,673
AB-4SL
6,200
4,975
Boron
AB-5S
350
648
AB-5SL
580
831
AB-7S
510
1,021
AB-7SL
2,000
1,257
AB-8S
1,700
1,769
AB-9BR
810
1,544
AS-1 S
3,000
3,383
MW-3S
860
1,472
MW-11 D
1,300
774

Table 5. Transport Model Calibration Results (cont.)
COI
Monitoring Well
Measured Concentration
(ug/L)
Predicted Concentration
(Ng/L)
Ash Basin Primary Cell/Ash Storage Constant Source Concentration = 3 - 28,000 pg/L
Ash Basin Secondary Cell Constant Source Concentration = 5 - 6,000 pg/L
AB-1 OS
44.7
47.6
AB-2S
1.8
1.7
AB-2SL
1.1
1.3
AB-3S
2.5
2.9
AB-4S
14.2
13.7
AB-4SL
2.8
11.6
AB-5SL
4.6
3.2
AB-6BRU
4.9
3.5
AB-8S
1.2
1.8
Cobalt
AB-9S
29.5
24.7
AS-1 S
356.0
357.1
AS-2 D
2.4
15.4
AS-3S
20.8
23.0
BG-3S
2.9
0.1
GWA-11 S
23.5
26.9
GWA-12S
2.4
0.0
GWA-22D
1.1
1.6
GWA-3S
2.2
2.3
GWA-41D
4.4
19.8
GWA-4S
2.2
0.3
GWA-5S
1.7
51.5
GWA-6BRU
2.8
7.5
GWA-6S
5.6
3.5
GWA-7S
8.9
0.0
GWA-81D
7.7
0.6
GWA-91D
1.5
6.1
GWA-9S
71.9
0.0
MW-6S
4.0
0.0
MW-3S
18.4
27.3
MW-7D
1.7
2.1
MW-8S
2.3
0.0
MW-8D
1.7
0.0
MW-11 S
2.2
1.0

Table 5. Transport Model Calibration Results (cont.)
COI
Monitoring Well
Measured Concentration
Ng/L)
Predicted Concentration
(Ng/L)
Sulfate
Ash Basin Primary Cell/Ash
Ash Basin Secondary
Storage Constant Source Concentration
Cell Constant Source Concentration
= 100,000-1,000,000 lag/L
= 100,000 - 1,800,000 lag/L
AB-10D
130,000
125,660
AB-2S
203,000
136,840
AB-2SL
125,000
158,800
AB-3S
105,000
94,456
AB-4S
82,700
133,920
AB-4SL
135,000
129,330
AB-5S
69,800
101,510
AB-5SL
10,400
102,180
AB-7S
61,700
112,760
AB-7SL
77,800
119,560
AB-8S
39,400
85,933
AB-9BR
111,000
101,030
AS-1 S
703,000
710,060
GWA-12S
199,000
80,526
GWA-2BR
162,000
115,260
GWA-3BRU
121,000
104,050
GWA-5BRU
119,000
149,770
GWA-6BR
482,000
380,040
GWA-6BRU
390,000
323,880
GWA-6S
280,000
155,300
GWA-7D
102,000
175,800
GWA-81D
198,000
79,589
GWA-9BR
187,000
271,500
GWA-91D
162,000
149,290
GWA-9S
123,000
1,962
MW-10D
397,000
280,000
Vanadium
Ash Basin Primary Cell/Ash Storage Constant Source Concentration = 10 - 16,000 lag/L
Ash Basin Secondary Cell Constant Source Concentration = 10 - 700 Ng/L
AB-1 OD
12.0
23.4
AB-1 OS
19.3
17.3
AB-2BR
28.8
2.3
AB-2S
304.0
303.0
AB-2SL
10.7
240.7
AB-31D
12.0
14.9
AB-3S
43.3
45.1

Table 5. Transport Model Calibration Results (cont.)
COI
Monitoring Well
Measured Concentration
(Ng/L)
Predicted Concentration
(Ng/L)
AB-4BR
34.2
38.8
AB-6BRU
37.0
35.4
AB-7SL
75.7
61.6
AB-8S
72.0
71.5
AB-9BR
17.9
16.0
AB-9BRU
17.3
51.0
AB-9S
12.3
43.7
AS-31D
12.8
19.1
AS-3S
88.2
91.8
BG-3BR
10.3
0.0
GWA-10D
14.0
20.1
Vanadium
(cont.)
GWA-10S
25.3
29.3
GWA-11S
67.9
66.8
GWA-1 D
14.0
0.0
GWA-22D
15.7
15.7
GWA-41D
21.2
11.5
GWA-4S
10.6
0.8
GWA-6BRU
10.2
18.2
GWA-6S
37.5
7.2
GWA-7D
40.7
1.1
GWA-7S
12.4
0.2
GWA-9BR
14.2
0.0
MW-8S
10.1
0.0
MW-91D
17.2
14.9
Chromium
Ash Basin Primary Cell/Ash Storage Constant Source Concentration = 5 - 3,500 Ng/L
Ash Basin Secondary Cell Constant Source Concentration = 2 - 5,000 Ng/L
AB-1 OD
13.7
14.4
AB-2SL
1.6
2.1
AB-4S
2.7
1.6
AB-4SL
3.2
1.3
AB-5SL
1.0
1.3
AB-6BRU
16.6
1.4
AB-7BRU
20.0
17.5
AB-7SL
2.2
93.4
AB-8S
1.5
0.9
AB-9BR
10.8
10.1
AS-31D
10.9
10.8
GWA-11 D
11.3
12.8

Table 5. Transport Model Calibration Results (cont.)
COI
Monitoring Well
Measured Concentration
N /L)
Predicted Concentration
(Ng/L)
Chromium
GWA-11 S
11.7
2.9
GWA-1 D
16.8
0.0
GWA-2BR
56.9
-0.1
GWA-6S
42.9
7.3
GWA-7S
65.4
2.1
MW-7S
10.2
11.7
Hexava lent
Chromium
Ash Basin Primary Cell/Ash Storage Constant Source Concentration = 20 - 27,500 Ng/L
Ash Basin Secondary Cell Constant Source Concentration = 5,000 - 10,000 pg/L
AB-2BR
1.3
0.0
AB-4BR
1.7
1.6
AB-7BRU
16.0
13.7
AB-9BR
1.7
4.1
GWA-1 D
15.0
0.0
GWA-1S
5.2
1.5
GWA-2BR
53.0
0.0
GWA-2BRU
2.3
1.4
GWA-6S
1.5
0.0

Table 6. MODPATH Advective Travel Time Results
Groundwater
Zone
Monitoring Well
Advective Travel Time to
Model Boundary ears
Shallow
AB-7S
11.0
AS -IS
51.5
GWA-1 S
38.9
GWA-3S
0.4
GWA-4S
40.7
GWA-5S
23.4
GWA-6S
12.7
GWA-9S
44.2
Deep
AS-2D
21.6
GWA-4D
1.5
GWA-5D
11.9
GWA-7D
7.9
GWA-8D
14.7
GWA-9D
12.3
Bedrock
AB-6BRU
5.7
AB-7BRU
2.1
AB-9BR
2.9
GWA-3BRU
0.7
GWA-6BR
3.2
GWA-9BR
22.9
GWA-12BRU
1.9

Table 7. Arsenic Transport Parameter Sensitivity Analysis
Well ID
Observed
Modeled
Porosity
kd ml/ ram
0.2
0.3
90
45
AB-2S
378
1389.31
1388.88
1389.31
1415.00
AB-2SL
1270
91.07
89.87
91.07
168.80
AB-3S
80.7
75.68
75.60
75.68
77.52
AB-1 D
0.25
0.00
0.00
0.00
0.00
AB-2D
0.33
0.00
0.00
0.00
0.03
AB-2BR
0.72
0.00
0.00
0.00
0.00
AB-3D
0.4
0.00
0.00
0.00
0.00
AB-1 OS
0.12
0.00
0.00
0.00
0.00
AB-10D
0.47
0.00
0.00
0.00
0.00
AS-1 S
5.8
0.00
0.00
0.00
0.00
AS-1 D
0.47
0.00
0.00
0.00
0.00
AS-2D
2.2
0.00
0.00
0.00
0.00
AS-3S
0.14
0.00
0.00
0.00
0.00
AS-3D
0.68
0.00
0.00
0.00
0.00
GWA-1 S
0.28
0.00
0.00
0.00
0.00
GWA-1 D
0.67
0.00
0.00
0.00
0.00
GWA-9S
0.14
0.00
0.00
0.00
0.00
GWA-9D
0.44
0.00
0.00
0.00
0.00
GWA-9BR
0.63
0.00
0.00
0.00
0.00
GWA-10S
0.18
0.00
0.00
0.00
0.00
GWA-10D
0.44
0.00
0.00
0.00
0.00
GWA-11 S
0.5
0.00
0.00
0.00
0.00
GWA-11 D
0.2
0.00
0.00
0.00
0.00
MW-7S
0.5
0.00
0.00
0.00
0.00
MW-7D
0.5
0.00
0.00
0.00
0.00
MW-9S
0.5
0.00
0.00
0.00
0.00
MW-9D
0.5
0.00
0.00
0.00
0.00

Table 8. Boron Transport Parameter Sensitivity Analysis
Well ID
Observed
Modeled
Porosity
0.2
0.3
AB-1 D
1500
2090.82
1895.48
Primary cell
(12045 days)
AB-21D
50
38.84
35.29
AB-10S
33
82.74
65.94
AS-1 S
2800
2355.96
2201.20
AS-1 D
360
1406.54
1259.39
AS-21D
490
25.51
17.08
AS-3S
50
0.00
0.00
AS-31D
50
0.00
0.00
GWA-81D
36
348.56
250.67
GWA-9S
300
306.68
152.28
GWA-91D
240
1548.87
1280.00
GWA-10D
50
0.00
0.00
AB-9S
28
546.13
530.11
Secondary cell
(21170 days)
GWA-3S
60
0.11
0.09
GWA-4S
250
265.43
203.44
GWA-41D
210
500.37
452.80
GWA-5S
50
337.92
313.18
GWA-6S
50
14.65
7.32
GWA-7S
50
78.46
43.70
GWA-7D
50
98.81
63.00
MW-3S
820
444.34
417.68
MW-3D
660
559.77
551.45
MW-11S
440
367.72
347.85
MW-11 D
1300
315.05
294.40
MW-12S
50
0.00
0.00
MW-12D
50
0.00
0.00

Figures
Figure 1. Conceptual Groundwater Flow Model/Model Domain(]
Figure 2. Model Domain North -South Cross Section (A -A') Through Secondary Ash BasinO
Figure 3. Model Domain East-West Cross Section (B-B') Through Primary and Secondary Ash BasinsM
Figure 4. Numerical Model Boundary Conditions0
Figure 5. Model Recharge Areas and Contaminant Source Zones (Constant Concentration Cells)0
Figure 6. Observation Wells in Shallow Groundwater ZoneO
Figure 7. Observation Wells in Deep Groundwater Zone0
Figure 8. Observation Wells in Bedrock Groundwater ZoneE
Figure 9. Hydraulic Conductivity Zonation in S/M1/M2 Layers (Model Layers 5-7z
Figure 10. Modeled Hydraulic Head (feet) vs. Observed Hydraulic Head (feet)m
Figure 11. Hydraulic Head (feet) in M2 Saprolite Layer (Model Layer 7)0
Figure 12. Hydraulic Head (feet) in North -South Cross Section (C-C') through Primary and Secondary
Ash Basins0
Figure 13. Hydraulic Head (feet) in East-West Cross Section (C-C') through Primary and Secondary Ash
Basins0
Figure 14. Particle Tracking Results (see Table. 6 for Advective Travel Times)0
Figure 15. Predicted Antimony (pg/L) in Monitoring Well GWA-3S for Model Scenarios 1-3m
Figure 16. Predicted Antimony (pg/L) in Monitoring Well GWA-4S for Model Scenarios 1-3m
Figure 17. Predicted Antimony (pg/L) in Monitoring Well GWA-5S for Model Scenarios 1-3m
Figure 18. Predicted Antimony (pg/L) in Monitoring Well GWA-12S for Model Scenarios 1-30
Figure 19. Predicted Antimony (pg/L) in Monitoring Well GWA-4D for Model Scenarios 1-3m
Figure 20. Predicted Antimony (pg/L) in Monitoring Well GWA-9D for Model Scenarios 1-3m
Figure 21. Predicted Antimony (pg/L) in Monitoring Well GWA-22D for Model Scenarios 1-3m
Figure 22. Predicted Antimony (pg/L) in Monitoring Well GWA-3BRU for Model Scenarios 1-3m
Figure 23. Predicted Antimony (pg/L) in Monitoring Well GWA-5BRU for Model Scenarios 1-3m
Figure 24. Predicted Antimony (pg/L) in Monitoring Well GWA-12BRU for Model Scenarios 1-30
Figure 25. Predicted Boron (pg/L) in Monitoring Well GWA-3S for Model Scenarios 1-30
Figure 26. Predicted Boron (pg/L) in Monitoring Well GWA-5S for Model Scenarios 1-30
Figure 27. Predicted Boron (pg/L) in Monitoring Well GWA-91D for Model Scenarios 1-30
Figure 28. Predicted Boron (pg/L) in Monitoring Well GWA-22D for Model Scenarios 1-30
Figure 29. Predicted Boron (pg/L) in Monitoring Well GWA-3BRU for Model Scenarios 1-K
Figure 30. Predicted Boron (pg/L) in Monitoring Well GWA-5BRU for Model Scenarios 1-K
Figure 31. Predicted Boron (pg/L) in Monitoring Well GWA-9BR for Model Scenarios 1-3m
Figure 32. Predicted Chromium (pg/L) in Monitoring Well GWA-3S for Model Scenarios 1-30
Figure 33. Predicted Chromium (pg/L) in Monitoring Well GWA-5S for Model Scenarios 1-3m
Figure 34. Predicted Chromium (pg/L) in Monitoring Well GWA-12S for Model Scenarios 1-3m
Figure 35. Predicted Chromium (pg/L) in Monitoring Well GWA-4D for Model Scenarios 1-3m
Figure 36. Predicted Chromium (pg/L) in Monitoring Well GWA-3BRU for Model Scenarios 1-30
Figure 37. Predicted Chromium (pg/L) in Monitoring Well GWA-5BRU for Model Scenarios 1-30
Figure 38. Predicted Chromium (pg/L) in Monitoring Well GWA-12BRU for Model Scenarios 1-30
Figure 39. Predicted Cobalt (pg/L) in Monitoring Well GWA-3S for Model Scenarios 1-3m
Figure 40. Predicted Cobalt (pg/L) in Monitoring Well GWA-4S for Model Scenarios 1-30
Figure 41. Predicted Cobalt (pg/L) in Monitoring Well GWA-5S for Model Scenarios 1-3m
Figure 42. Predicted Cobalt (pg/L) in Monitoring Well GWA-9S for Model Scenarios 1-3m
Figure 43. Predicted Cobalt (pg/L) in Monitoring Well GWA-12S for Model Scenarios 1-3m
Figure 44. Predicted Cobalt (pg/L) in Monitoring Well GWA-4D for Model Scenarios 1-3]
Figure 45. Predicted Cobalt (pg/L) in Monitoring Well GWA-9D for Model Scenarios 1-30

Figure 46. Predicted Cobalt (pg/L) in Monitoring Well GWA-22D for Model Scenarios 1-3m
Figure 47. Predicted Cobalt (pg/L) in Monitoring Well GWA-3BRU for Model Scenarios 1-30
Figure 48. Predicted Cobalt (pg/L) in Monitoring Well GWA-5BRU for Model Scenarios 1-3m
Figure 49. Predicted Cobalt (pg/L) in Monitoring Well GWA-12BRU for Model Scenarios 1-32
Figure 50. Predicted Hexavalent Chromium (pg/L) in Monitoring Well GWA-3S for Model Scenarios 1-3M
Figure 51. Predicted Hexavalent Chromium (pg/L) in Monitoring Well GWA-4S for Model Scenarios 1-30
Figure 52. Predicted Hexavalent Chromium (pg/L) in Monitoring Well GWA-5S for Model Scenarios 1-3M
Figure 53. Predicted Hexavalent Chromium (pg/L) in Monitoring Well GWA-41D for Model Scenarios 1-30
Figure 54. Predicted Hexavalent Chromium (pg/L) in Monitoring Well GWA-9D for Model Scenarios 1-30
Figure 55. Predicted Hexavalent Chromium (pg/L) in Monitoring Well GWA-22D for Model Scenarios 1-3M
Figure 56. Predicted Hexavalent Chromium (pg/L) in Monitoring Well GWA-3BRU for Model Scenarios 1-
3M
Figure 57. Predicted Hexavalent Chromium (pg/L) in Monitoring Well GWA-5BRU for Model Scenarios 1-
3M
Figure 58. Predicted Sulfate (pg/L) in Monitoring Well GWA-41D for Model Scenarios 1-30
Figure 59. Predicted Sulfate (pg/L) in Monitoring Well GWA-91D for Model Scenarios 1-3m
Figure 60. Predicted Sulfate (pg/L) in Monitoring Well GWA-5BRU for Model Scenarios 1-30
Figure 61. Predicted Sulfate (pg/L) in Monitoring Well GWA-9BR for Model Scenarios 1-3m
Figure 62. Predicted Vanadium (pg/L) in Monitoring Well GWA-3S for Model Scenarios 1-3m
Figure 63. Predicted Vanadium (pg/L) in Monitoring Well GWA-4S for Model Scenarios 1-31a
Figure 64. Predicted Vanadium (pg/L) in Monitoring Well GWA-5S for Model Scenarios 1-3m
Figure 65. Predicted Vanadium (pg/L) in Monitoring Well GWA-9S for Model Scenarios 1-30
Figure 66. Predicted Vanadium (pg/L) in Monitoring Well GWA-12S for Model Scenarios 1-3m
Figure 67. Predicted Vanadium (pg/L) in Monitoring Well GWA-41D for Model Scenarios 1-3m
Figure 68. Predicted Vanadium (pg/L) in Monitoring Well GWA-91D for Model Scenarios 1-3m
Figure 69. Predicted Vanadium (pg/L) in Monitoring Well GWA-22D for Model Scenarios 1-30
Figure 70. Predicted Vanadium (pg/L) in Monitoring Well GWA-3BRU for Model Scenarios 1-3m
Figure 71. Predicted Vanadium (pg/L) in Monitoring Well GWA-5BRU for Model Scenarios 1-3m
Figure 72. Predicted Vanadium (pg/L) in Monitoring Well GWA-9BR for Model Scenarios 1-3m
Figure 73. Predicted Vanadium (pg/L) in Monitoring Well GWA-12BRU for Model Scenarios 1-30
Figure 74. Initial (2015) Antimony Concentrations (pg/L) in the Shallow Groundwater Zonem
Figure 75. Initial (2015) Antimony Concentrations (pg/L) in the Deep Groundwater Zonem
Figure 76. Initial (2015) Antimony Concentrations (pg/L) in the Bedrock Groundwater Zonem
Figure 77. "Existing" Scenario 1 - 2115 Predicted Antimony (pg/L) in the Shallow Groundwater ZoneM
Figure 78. "Existing" Scenario 1 - 2115 Predicted Antimony (pg/L) in the Deep Groundwater ZoneM
Figure 79. "Existing" Scenario 1 - 2115 Predicted Antimony (pg/L) in the Bedrock Groundwater ZoneM
Figure 80. "Cap -In -Place" Scenario 2 - 2115 Predicted Antimony (pg/L) in the Shallow Groundwater ZoneM
Figure 81. "Cap -In -Place" Scenario 2 - 2115 Predicted Antimony (pg/L) in the Deep Groundwater ZoneM
Figure 82. "Cap -In -Place" Scenario 2 - 2115 Predicted Antimony (pg/L) in the Bedrock Groundwater Zone[N
Figure 83. "Excavate" Scenario 3 - 2115 Predicted Antimony (pg/L) in the Shallow Groundwater ZoneM
Figure 84. "Excavate" Scenario 3 - 2115 Predicted Antimony (pg/L) in the Deep Groundwater ZoneM
Figure 85. "Excavate" Scenario 3 - 2115 Predicted Antimony (pg/L) in the Bedrock Groundwater M ZoneM
Figure 86. Initial (2015) Boron Concentrations (pg/L) in the Shallow Groundwater Zonem
Figure 87. Initial (2015) Boron Concentrations (pg/L) in the Deep Groundwater Zonem
Figure 88. Initial (2015) Boron Concentrations (pg/L) in the Bedrock Groundwater Zonem
Figure 89. "Existing" Scenario 1 - 2115 Predicted Boron (pg/L) in the Shallow Groundwater ZoneM
Figure 90. "Existing" Scenario 1 - 2115 Predicted Boron (pg/L) in the Deep Groundwater Zonem
Figure 91. "Existing" Scenario 1 - 2115 Predicted Boron (pg/L) in the Bedrock Groundwater ZoneM
Figure 92. "Cap -In -Place" Scenario 2 - 2115 Predicted Boron (pg/L) in the Shallow Groundwater ZoneM
Figure 93. "Cap -In -Place" Scenario 2 - 2115 Predicted Boron (pg/L) in the Shallow Groundwater ZoneM

Figure 94. "Cap -In -Place" Scenario 2 - 2115 Predicted Boron (pg/L) in the Bedrock Groundwater ZoneM
Figure 95. "Excavate" Scenario 3 - 2115 Predicted Boron (pg/L) in the Shallow Groundwater ZoneM
Figure 96. "Excavate" Scenario 3 - 2115 Predicted Boron (pg/L) in the Deep Groundwater Zonem
Figure 97. "Excavate" Scenario 3 - 2115 Predicted Boron (pg/L) in the Bedrock Groundwater ZoneM
Figure 98. Initial (2015) Chromium Concentrations (pg/L) in the Shallow Groundwater Zonem
Figure 99. Initial (2015) Chromium Concentrations (pg/L) in the Deep Groundwater Zonem
Figure 100. Initial (2015) Chromium Concentrations (pg/L) in the Bedrock Groundwater Zonem
Figure 101. "Existing" Scenario 1 - 2115 Predicted Chromium (pg/L) in the Shallow Groundwater ZoneM
Figure 102. "Existing" Scenario 1 - 2115 Predicted Chromium (pg/L) in the Deep Groundwater ZoneM
Figure 103. "Existing" Scenario 1 - 2115 Predicted Chromium (pg/L) in the Bedrock Groundwater ZoneM
Figure 104. "Cap -In -Place" Scenario 2 - 2115 Predicted Chromium (pg/L) in the Shallow Groundwater
Zone
Figure 105. "Cap -In -Place" Scenario 2 - 2115 Predicted Chromium (pg/L) in the Deep Groundwater ZoneM
Figure 106. "Cap -In -Place" Scenario 2 - 2115 Predicted Chromium (pg/L) in the Bedrock M Groundwater
ZoneM
Figure 107. "Excavate" Scenario 3 - 2115 Predicted Chromium (pg/L) in the Shallow Groundwater ZoneM
Figure 108. "Excavate" Scenario 3 - 2115 Predicted Chromium (pg/L) in the Deep Groundwater ZoneM
Figure 109. "Excavate" Scenario 3 - 2115 Predicted Chromium (pg/L) in the Bedrock Groundwater ZoneM
Figure 110. Initial (2015) Cobalt Concentrations (pg/L) in the Shallow Groundwater Zonem
Figure 111. Initial (2015) Cobalt Concentrations (pg/L) in the Deep Groundwater Zonem
Figure 112. Initial (2015) Cobalt Concentrations (pg/L) in the Bedrock Groundwater Zonem
Figure 113. "Existing" Scenario 1 - 2115 Predicted Cobalt (pg/L) in the Shallow Groundwater ZoneM
Figure 114. "Existing" Scenario 1 - 2115 Predicted Cobalt (pg/L) in the Deep Groundwater ZoneM
Figure 115. "Existing" Scenario 1 - 2115 Predicted Cobalt (pg/L) in the Bedrock Groundwater ZoneM
Figure 116. "Cap -In -Place" Scenario 2 - 2115 Predicted Cobalt (pg/L) in the Shallow Groundwater ZoneM
Figure 117. "Cap -In -Place" Scenario 2 - 2115 Predicted Cobalt (pg/L) in the Deep Groundwater ZoneM
Figure 118."Cap-In-Place" Scenario 2 - 2115 Predicted Cobalt (pg/L) in the Bedrock Groundwater ZoneM
Figure 119. "Excavate" Scenario 3 - 2115 Predicted Cobalt (pg/L) in the Shallow Groundwater ZoneM
Figure 120. "Excavate" Scenario 3 - 2115 Predicted Cobalt (pg/L) in the Deep Groundwater ZoneM
Figure 121. "Excavate" Scenario 3 - 2115 Predicted Cobalt (pg/L) in the Bedrock Groundwater ZoneM
Figure 122. Initial (2015) Hexavalent Chromium Concentrations (pg/L) in the Shallow Groundwater ZoneM
Figure 123. Initial (2015) Hexavalent Chromium Concentrations (pg/L) in the Deep Groundwater ZoneM
Figure 124. Initial (2015) Hexavalent Chromium Concentrations (pg/L) in the Bedrock Groundwater ZoneM
Figure 125. "Existing" Scenario 1 - 2115 Predicted Hexavalent Chromium (pg/L) in the Shallow
Groundwater ZoneM
Figure 126. "Existing" Scenario 1 - 2115 Predicted Hexavalent Chromium (pg/L) in the Deep Groundwater
Zone
Figure 127. "Existing" Scenario 1 - 2115 Predicted Hexavalent Chromium (pg/L) in the Bedrock
Groundwater ZoneM
Figure 128. "Cap -In -Place" Scenario 2 - 2115 Predicted Hexavalent Chromium (pg/L) in the Shallow
Groundwater ZonedO
Figure 129. "Cap -In -Place" Scenario 2 - 2115 Predicted Hexavalent Chromium (pg/L) in the Deep
Groundwater ZoneM
Figure 130. "Cap -In -Place" Scenario 2 - 2115 Predicted Hexavalent Chromium (pg/L) in the Bedrock
Groundwater Zone[N
Figure 131. "Excavate" Scenario 3 - 2115 Predicted Hexavalent Chromium (pg/L) in the Shallow
Groundwater ZoneM
Figure 132. "Excavate" Scenario 3 - 2115 Predicted Hexavalent Chromium (pg/L) in the Deep
Groundwater ZoneM

Figure 133. "Excavate" Scenario 3 - 2115 Predicted Hexavalent Chromium (pg/L) in the Bedrock
Groundwater ZoneM
Figure 134. Initial (2015) Sulfate Concentrations (pg/L) in the Shallow Groundwater Zonem
Figure 135. Initial (2015) Sulfate Concentrations (pg/L) in the Deep Groundwater Zonem
Figure 136. Initial (2015) Sulfate Concentrations (pg/L) in the Bedrock Groundwater Zonem
Figure 137. "Existing" Scenario 1 - 2115 Predicted Sulfate (pg/L) in the Shallow Groundwater ZoneM
Figure 138. "Existing" Scenario 1 - 2115 Predicted Sulfate (pg/L) in the Deep Groundwater ZoneM
Figure 139. "Existing" Scenario 1 - 2115 Predicted Sulfate (pg/L) in the Bedrock Groundwater ZoneM
Figure 140. "Cap -In -Place" Scenario 2 - 2115 Predicted Sulfate (pg/L) in the Shallow Groundwater ZoneM
Figure 141. "Cap -In -Place" Scenario 2 - 2115 Predicted Sulfate (pg/L) in the Deep Groundwater ZoneM
Figure 142. "Cap -In -Place" Scenario 2 - 2115 Predicted Sulfate (pg/L) in the Bedrock Groundwater ZoneM
Figure 143. "Excavate" Scenario 3 - 2115 Predicted Sulfate (pg/L) in the Shallow Groundwater ZoneM
Figure 144. "Excavate" Scenario 3 - 2115 Predicted Sulfate (pg/L) in the Deep Groundwater ZoneM
Figure 145. "Excavate" Scenario 3 - 2115 Predicted Sulfate (pg/L) in the Bedrock Groundwater ZoneM
Figure 146. Initial (2015) Vanadium Concentrations (pg/L) in the Shallow Groundwater Zonem
Figure 147. Initial (2015) Vanadium Concentrations (pg/L) in the Deep Groundwater Zonem
Figure 148. Initial (2015) Vanadium Concentrations (pg/L) in the Bedrock Groundwater Zonem
Figure 149. "Existing" Scenario 1 - 2115 Predicted Vanadium (pg/L) in the Shallow Groundwater M ZoneM
Figure 150. "Existing" Scenario 1 - 2115 Predicted Vanadium (pg/L) in the Deep Groundwater ZoneM
Figure 151. "Existing" Scenario 1 - 2115 Predicted Vanadium (pg/L) in the Bedrock Groundwater 0 ZoneM
Figure 152. "Cap -In -Place" Scenario 2 - 2115 Predicted Vanadium (pg/L) in the Shallow Groundwater
Zone
Figure 153. "Cap -In -Place" Scenario 2 - 2115 Predicted Vanadium (pg/L) in the Deep Groundwater ZoneM
Figure 154. "Cap -In -Place" Scenario 2 - 2115 Predicted Vanadium (pg/L) in the Bedrock Groundwater
ZoneM
Figure 155. "Excavate" Scenario 3 - 2115 Predicted Vanadium (pg/L) in the Shallow Groundwater ZoneM
Figure 156. "Excavate" Scenario 3 - 2115 Predicted Vanadium (pg/L) in the Deep Groundwater ZoneM
Figure 157. "Excavate" Scenario 3 - 2115 Predicted Vanadium (pg/L) in the Bedrock Groundwater ZoneM

Vroundi
Discus
No Pi,.
0( U13%,i 101 Sc
Figure 1. Conceptual Groundwater Flow Model/Model Domain

A .°
Figure 2. Model Domain North -South Cross Section (A -A') Through Secondary Ash BasinO

Figure 3. Model Domain East-West Cross Section (B-B') Through Primary and Secondary Ash Basins

Figure 4. Numerical Model Boundary Conditions

ACTIVE
_ `\ .ASH BASIN
Q =. L•�OLD PRIMARY ACTIVE..
'CELL ASH BASIN I
SECONDARY
E%f 'G0ri tart. CELL
Centratlon
SOU rcC,
r
co�� harge =�6 irtJ;yr
lll
t' #
ACTIVE -�
ASH BASIN
PRIMARY CELL
Recharge = 6 inlyr yti.
Constant ASH
I Concentration s-rORAGE t
$r�ll1'CP �a •
R
{ L '
i Recharge = 5 inlyear n
MODE L G`bU hDA R Y Q 500 1.000
Feet
lo
' �*` • a 1jr a Gsrn a apping, r
I. �4 IG� {any' f rpfg �. cr rtorytaieih
Figure 5. Model Recharge Areas and Contaminant Source Zones (Constant Concentration Cells)

Figure 6. Observation Wells in Shallow Groundwater Zone

Figure 7. Observation Wells in Deep Groundwater Zone

Figure 8. Observation Wells in Bedrock Groundwater Zone

. Ntsz
rX ?
Figure 9. Hydraulic Conductivity Zonation in S/M1/M2 Layers (Model Layers 5-7

710
700
WEI
I
O
m
N
c 670
v
0660
650
AI
30
Observed head, ft
Figure 10. Modeled Hydraulic Head (feet) vs. Observed Hydraulic Head (feet)

' �
gr
ACTIVE
ASH BASIN ACTIVE
OLD PRIMARY CELL ASH BASIN
SECONDARY
pp�NpPY CELL
�P
4
r
rAy ACTIVE
ASH BASIN
PRIMARY CELL ASH `
STORAGE 1
r - y
I I
r
r
r r FACDEL BOUNDA Y
r j ui e. Csr11 1 �<
y Z .;tiN -3P 2111 1,-,7 9. IV, Fwirb•
Figure 11. Hydraulic Head (feet) in M2 Saprolite Layer (Model Layer 7)
N
A
0 500 1_000
Feet

Figure 12. Hydraulic Head (feet) in North -South Cross Section (C-C') through Primary and Secondary Ash Basins

M
A
a
Figure 13. Hydraulic Head (feet) in East-West Cross Section (C-C') through Primary and Secondary Ash Basins

Figure 14. Particle Tracking Results (see Table. 6 for Advective Travel Times)

Predicted Antimony at GWA-3S
Scenario 1 - Existing Condition
Scenario 2 - Cap -in -Place
7 ...,., ,.,.,. ,.,.. Scenario 3-Excavation
1MAC/2L Standard — —
Be............... ................ .................... :........:........... ............... :...................:........:........
5
7,
q
.......... ......... ......... ......... .......,....... ,,.. ,.........,:,...... ....., ...... ..... ..... ...... .......
3
......................................................................................................... .......r......... .....
2-I...................................... e........................ ................ I ............... I...............
Ln u-) to u') Ln Ln +n Ln an 4n Ln sn Ur, Ln u)
cO 06 o N rS to CO O N 7 n Go o N It LO
G� M Q O O G O N N C+] N
r N N N CV N N N N N N N {V N N
Figure 15. Predicted Antimony (pg/L) in Monitoring Well GWA-3S for Model Scenarios 1-3

E4
1.8
1.6
1.4
1w,
0.6
0.4
0.2
0
Predicted Antimony at GWA-4S
U') U7 u] 0 Ln In Ln U7 Ln U7 U7 u7 LO LO Ln LO
i0 M C3 N IT CD 00 CO C7 N "C (0
65 m Q C) CD P Q Cv N N N
r T N CV N N N N N RI CV N CV N CQ N
Figure 16. Predicted Antimony (pg/L) in Monitoring Well GWA-4S for Model Scenarios 1-3

Predicted Antimony at GWA-5S
40
35 -{...........................................
30 �................ I . . I .-, ................... I I . I I — I I . I .
Scenario 1 - Existing Condition
Scenario 2 - Cap -in -Place
Scenario 3 - Excavation
IMAG/2L Standard
25
....... .. ..................... ....... ........ .............. ...................... ..........
0
20
..................... .. .................. ....... ............. ...... ........ ......
<
15
.................... ........ ...................... .... ....... ....... .................... ....... ..........
10 i I - .- I I .... I - .......... Yp- ........ .......I . i . I . I ... : ... I ... I ........... . I . I ..................
I
. . . . . . . .. . . . . . . / .................... ............................ .............. ....... ....... ....... ...... I ..........
LO LO LO LO LO LO LO LO LO LO LO LO Li LO LO LO
(D 00 C3 CM iD 00 0 C11 (0 cc 0 C\I w
0 C) C) 0 N N ;n C\j
N N N N N N N N CN N N N C%d 04
Figure 17. Predicted Antimony (pg/L) in Monitoring Well GWA-5S for Model Scenarios 1-3

1.6
1.4
1.2
1
a
p 0.8
E
d
0.6
0.4
ME,
0
Predicted Antimony at GWA-12S
U', u') u') en un In In Ln an LO un un un
ifl OC7 Q N IT (O CO Q N cS (4 Q N "C CO
6'� @ O Q Q Q Q CV N N N
r T N N N N N N N RI N N CV N CQ N
Figure 18. Predicted Antimony (Ng/L) in Monitoring Well GWA-12S for Model Scenarios 1-3

Predicted Antimony at GWA-41D
..............................,. ...,,.,..,......,..
..... .. ..... ..... " ...... : ...... : ...... : .
s,........ ...... ...... ..,,. ...,, ..... .........................
s -1 ...: ........: .... .
2 -I .....,
0
ui
LO
I
un
O
4
N
T.
U') Ln
CIj rp
O O
N N
un
f57
G
N
T
+n Ln
CO O
4
N N
Lry 4fi �fi Ln U'7
CV 7 fO Go O
N N N N N
Figure 19. Predicted Antimony (pg/L) in Monitoring Well GWA-413 for Model Scenarios 1-3
U ] U-) Lai
C\jN tt N
N N N
N N N

12
r
8
a
O 6
E
4
0
Predicted Antimony at GWA-91D
u7 u') Ur, Ln Ln 4n u7 Ln 4n Ln Ln u) 1n u� u)
CO rx3 O {v tt CO CO o N eC (n aO o N 'c1' CO
O� i35 Q p q G o N N N N
r r N N N N N N N N N N N N N N
Figure 20. Predicted Antimony (pg/L) in Monitoring Well GWA-913 for Model Scenarios 1-3

Predicted Antimony at GWA-22D
Ln in UI) LO Ln un +n Ln an 4n U', Lr) an Un LO U)
CO 03 o N rS CO CO I CV 'c7 CO Go CD N 7 (O
G� <i) Q p C7 G Q N N C+j N
r N N N CV N CV N N N N N N N N
Figure 21. Predicted Antimony (pg/L) in Monitoring Well GWA-22D for Model Scenarios 1-3

Predicted Antimony at GWA-3BRU
7 -1 . ...... .-
6 -1 ..........................................I.......... ................................................
5
4 ...... ....... .,... . ,.... ....,.. _ .,,.,
E
... ... .. ... .. ...........................
2 = .—..................................... ..I ....... ,.... ...:........... I ................................ I
0
Ln
cn
G�
u� U') u') Ln un +n Ln Ln 4n U', Ln +n u') Ln U)
CO o C'Ij rp to CO O N 'C fn tO o N It rO
<i) Q O O G O N N C+] N
N N N CV N N N (M N CV N N N N
Figure 22. Predicted Antimony (fag/L) in Monitoring Well GWA-313RU for Model Scenarios 1-3

45
40
35
30
25
0
E
20
d
15
10
5
0
Predicted Antimony at GWA-5BRU
u-j u") U') n) Ln Ln u) u5 Ln Ln Ln uz +n Xn u') un
CO 00 O N tr CO CO N 'R [0 00 CDN �t CO
CD CDq CD CD N N N N
r r N N N N N N N N N N N N N N
Figure 23. Predicted Antimony (fag/L) in Monitoring Well GWA-513RU for Model Scenarios 1-3

Predicted Antimony at GWA-12BRU
1.2 d -
0.8
a
0
E
0.6
d
0.4 �
0.2 -1 .... ...
M C7 N C• CD CO Q N cS cc CO CD N 7 [O
0 Q Q P 0 CV N N N
T N N N N N N ftf RI CV N N N N N
Figure 24. Predicted Antimony (pg/L) in Monitoring Well GWA-12BRU for Model Scenarios 1-3

Predicted Boron at GWA-3S
800
700
_
.
_
-
- - -
-
600
..................
.........
.......
.......
-�
500
....
..........
.......
............
...:
p
400
. ...........
..'.......:........:.......
a
m
300......
........
.........
...:....
..:.........
............
.:.........
.
200
:........:.....
.. ..
100
.......
...............
.:.. ....:.
....:........
..............:........
0
Q
m
CD04
coo
OD
CCv
Q
r
T
N
N
N
N CV
N CV
N
ftf RI
CO O N 7 CO
CV N N N
N CV N N CV
Figure 25. Predicted Boron (Pg/L) in Monitoring Well GWA-3S for Model Scenarios 1-3

3000
2500
2000
c
1500
0
m
1000
50❑
C
Predicted Boron at GWA-5S
U') Ln u') +n U� Ur, Ln Ln Ln u7 to in Ln Ln Ln
CO 00 O N IT [O CO C7 N '7 fO m O N CO
67 9) o Q Q Q Q fV CV N N
T r N N N N N N N N N N N N N N
Figure 26. Predicted Boron (Pg/L) in Monitoring Well GWA-5S for Model Scenarios 1-3

2000
A
Predicted Boron at GWA-91D
Scenario 1 - Existing Condition
Scenario 2 - Cap -in -Place
Scenario 3 - Excavation
NAC/2L Standard — —
LrI Lr, u') +n Ln 4n Ln Ln n to Ur cn Lr, u)
CO 00 O N ei [n CO O CV '7 CO m <D ,N IT [O
67 Q O Q CDQ fV N N N
T r N N N N N N N N N CV SV N N N
Figure 27. Predicted Boron (pg/L) in Monitoring Well GWA-913 for Model Scenarios 1-3

Predicted Boron at GWA-22D
1400 . , . , . Scenario 1 - Existing Condition
Scenario 2 - Cap -in -Place
Scenario 3 - Excavation
NAC/2L Standard — —
1200 ..... : ..............
1000 �` .
800
o- - - - - - - - - - - ---
0
M 600
400 .. ..............................
,
200
0 1 1 -.. �. ._
Ln LC] Ln Ln Ln Ln Ln U') 0 0 0 In 0 Ui LS] Lr)
CD 00 CD I LO CO Q C� _ CD co CD
67 m CDO Q CD O CV N N N
T r N N N N CV N N N N N N N N N
Figure 28. Predicted Boron (pg/L) in Monitoring Well GWA-22D for Model Scenarios 1-3

Predicted Boron at GWA-3BRU
Scenario 1 - Existing Condition
800 Scenario 2 - Cap -in -Place
Scenario 3 - Excavation
[MAC/2L Standard — —
700 — — — — — — — — — — — — — — — — — — — — — — — —
600.....:.......:.......:.......:.......".......:......... ...............:.......:. ......:..... .
03 500:........ ....... :........ ........ ..........
a 400 :.......... ......:....... :........:..........
Cfl
300 1 ....I; ......: ........ \...... :..... X.:......................................... .. ._. ..
200 1 r ......... ..........\—............ \...........................
100 �.. I .............. I-......1..... .,I,.`.... .... ..11-1........
.. ......
3-W��
lD OD Q N t'C CD CO Q N cS (D CO Q N 7 [O
U? o Q Q Q Q CV N N N
r N N N N N N N RI CV Ti CV N N N
Figure 29. Predicted Boron (pg/L) in Monitoring Well GWA-3BRU for Model Scenarios 1-3

c
0
Predicted Boron at GWA-5BRU
5000
4000
3000
2000
0 T
Ln sn Ln Ln Ln 4n Ln Ln
0 CO Q N V [n CO O
0) O Q Q Q o Q
r N N N N N N
Scenario 1 - Existing Condition
Scenario 2 - Cap -in -Place
Scenario 3 - Excavation
IMAC/2L Standard — —
Ln Ln
CU
'7
CO
m
Q
N
tc
CV
N
N N
N
N
N
N
N
N
N N
Figure 30. Predicted Boron (pg/L) in Monitoring Well GWA-5BRU for Model Scenarios 1-3

Predicted Boron at GWA-9BR
Scenario 1 - Existing Condition
4000
Scenario 2 - Cap -in -Place
. ............
Scenario 3 - Excavation
NAC/2L Standard
3500 ........... ............. ..... /...........
......... ....... ..............................................................
3000 1 1 , ...... I , ....... I .... I - - I ....... - - - I ................................. I ....... I ...... I .............. I I -
03 2500 . ............ . . ..... ... ....... ....... ........................ ........ ................. ...............................
2000 . ............ ....... ....... ....... ................ ........ ........ ........ ....... ................
m A:
1500 -1 T A ....... ............ .................. ..................................
1000 -1 ........... : ...... I ............. \.: ... — N........................... ........ ............ .............. .............. —
500
T
.......... ........
LO Ln �n Ln Ln U'j Kn LO LO U') U') In Lr) U-) Ln Ln
(D CO CD IN a aes e0 0 CD 03 <D �T to
m CD Q Q CV CIA N NN N N N N 7q N N N N (Ij 0i N N
Figure 31. Predicted Boron (pg/L) in Monitoring Well GWA-9BR for Model Scenarios 1-3

100
80
�7
60
E
_Z
E
Q
C) 40
20
0
Predicted Chromium at GWA-3S
Ln Lr) u') Ln Ln 0 L U') u) U') Ln to Ln Ln Ln Ln
in M Q LV C CD 00 Q N cS (4 CO CD 7 [O
Q CD Q Q CV RI N CV
r T N N N Ci N N N N CV N C.1 N N N
Figure 32. Predicted Chromium (Pg/L) in Monitoring Well GWA-3S for Model Scenarios 1-3

1200
1000
�7
800
E
__5
E 600
Q
0
400
200
C
Predicted Chromium at GWA-5S
Ln in Ln Ln Ln U') Ln Urr u') an u') Ln sn u O Ln It)
0 00 O N rl' (n CO O CU '7 (O tr] <D N �T CO
14 GI 0) Q P Q C7 C7 fV N N N
r N N N N N N N N N N N N CV N
Figure 33. Predicted Chromium (Pg/L) in Monitoring Well GWA-5S for Model Scenarios 1-3

200
150
E
100
E
0
50
0
Predicted Chromium at GWA-12S
Ln Ln u') 0 Ln In Ln U') Ln U') Ln un Ln a) Ln uz
ifl OC7 Q N IT CD 00 Q N cS (4 CO ID "C Cf7
6) CD O Q CD CV N N N
r T N N N N N N N RI CV N N N N N
Figure 34. Predicted Chromium (lag/L) in Monitoring Well GWA-12S for Model Scenarios 1-3

12
E
8
�7
E
6
E
Q
0
4
2
0
Predicted Chromium at GWA-41D
U') u5 ;n In Ln Ln 4n u') Ln 4n u') un u') Lr) u� u)
[P 00 o N ZY cn CO o N eC (t7 a0 4 N et rn
O� tr C CD CD CD CD N N N N
r r N N N N N N N N N N N N N N
Figure 35. Predicted Chromium (pg/L) in Monitoring Well GWA-413 for Model Scenarios 1-3

90
80
70
60
�7
E 50
E
Q
s 40
0
30
20
10
0
Predicted Chromium at GWA-3BRU
Un u') tn U'j LO U') to to sn >n n X) LO Ln Ln us
[D OD 0 N a fD CO 0 N v (D CO 0 N v [D
CS) !P 0 0 0 C:> 0 N N N N
r N N N N N N N N N N N N N N
Figure 36. Predicted Chromium (Ng/L) in Monitoring Well GWA-3BRU for Model Scenarios 1-3

1200
1000
p7 80❑
E
_Z5
E 600
0
400
200
0
Predicted Chromium at GWA-5BRU
La U7 U] Ln Ui U7 U7 U7 U7 U7 0 U7 U7 U7 U] U7
0 00 o N R (O 07 O CU '7 (.O trQ O N IT LO
W 9) Q P Q O Q fV N CV N
r r N N N N N N N N N N N N N N
Figure 37. Predicted Chromium (fag/L) in Monitoring Well GWA-5BRU for Model Scenarios 1-3

180
160
140
120
�7
E 100
_Z5
E
Q
�z 80
0
60
40
20
0
Predicted Chromium at GWA-12BRU
to un �n 0 Sn in to u Ln r uI +n 4n Ln Ln u)
iD M C7 CV CT 2 Ob +D N (D CO O N ! [p
CA C? Q 0 0 0 N N N N
T N N N N N N N RI N N CV N CQ N
Figure 38. Predicted Chromium (Pg/L) in Monitoring Well GWA-12BRU for Model Scenarios 1-3

c 4
0
Predicted Cobalt at GWA-3S
- Scenario 1 - Existing Condition
Scenario 2 - Cap-in-Place
.........:........:...,.,...........:,......:.,.....:................:.....,..'... Scenario 3 Excavation
NAC/2L Standard — —
u-) u') u') Ln Uri +n u3 T) Ln Lr, u') +n cn u)
C6 CDCq 'S fn a] O N 'C fO [(7 O N 17 [O
0 Q C] CD G 4 N N C+j N
T r N N N CV N N N N N t'.1 N CJ N N
Figure 39. Predicted Cobalt (pg/L) in Monitoring Well GWA-3S for Model Scenarios 1-3

0
25
20
IL
5
0
u-j u'S u')
CO m CD6 it C
r r N
Predicted Cobalt at GWA-45
Scenario 1 - Existing Condition
Scenario 2 - Cap -in -Place
Scenario 3 - Excavation
NAC/2L Standard — —
:... ..:..............
Tn
Ln
Ln
u')
qn
Ln Ln
N R
CA
07
N
eC
[L7
00
4
N
4` [O
CD CD
CD
o
N
N
N N
N N
N
N
N
N
N
N
N
N
N
N N
Figure 40. Predicted Cobalt (pg/L) in Monitoring Well GWA-4S for Model Scenarios 1-3

Predicted Cobalt at GWA-5$
160 -I
140 -1 . .......................................
120
Scenario 1 - Existing Condition
Scenario 2 - Cap -in -Place
Scenario 3 - Excavation
[MAC/2L Standard — —
100
80
......
40 _ .,. ...... .... ....... ............ ..............
20 . ...... ...... . ...... . ...... ...... ........
,...........................
....,. ......
0
ifl O'] O N tT CD 00 CO O N !I, LQ
0 Q 0 O Q CV N N N
r T N N N N N N N RI CV N CV N N N
Figure 41. Predicted Cobalt (pg/L) in Monitoring Well GWA-5S for Model Scenarios 1-3

45
40
35
c,C
25
c[i
U 20
Predicted Cobalt at GWA-9S
n u') u') Un in U') un in en sn us sn Ln Ln Ln u')
[D Co O CV (F Cp O N V (D O N (L3
CS7 W O O 4 4 C7 N N N N
r N N N N N N N N N N N N N N
Figure 42. Predicted Cobalt (Ng/L) in Monitoring Well GWA-9S for Model Scenarios 1-3

4
3.5
3
2.5
c 2
0
I
0.5
0
Predicted Cobalt at GWA-12S
Ur; U') U') en un u') on U') u') Ln an un u) un U)
iO OD C] N IT (D CO N cS (O CO 0 N !I, [O
C Q O P C? CA N N N
r T N N N N hl N N RI CV N N N N N
Figure 43. Predicted Cobalt (Pg/L) in Monitoring Well GWA-12S for Model Scenarios 1-3

100
80
60
ca
40
20
0
Predicted Cobalt at GWA-4D
in Lr) Ln Ln Ln Ln Ln u Ln u') uI Ln u') Ln Ln Ln
lD m O CV t'C CO 00 +D N cS (D CO O N 7 CO
C? O 9 P O CV N N N
r T N N [N N N N N RI N N N N N N
Figure 44. Predicted Cobalt (fag/L) in Monitoring Well GWA-4D for Model Scenarios 1-3

700
600
500
400
t� 300
200
100
0
Predicted Cobalt at GWA-9D
U', u U') in Ln In Ln U') u') U') U1 un u') un U) It)
to m C] N S4 (O 00 O N cS (D CO Q N 7 CO
6? C Cy Q Q Q CV N N N
r T N N N N N N ftf RI N N N N N N
Figure 45. Predicted Cobalt (fag/L) in Monitoring Well GWA-913 for Model Scenarios 1-3

Predicted Cobalt at GWA-22D
Scenario 1 - Existing Condition
Scenario 2 - Cap -in -Place
Scenario 3 - Excavation
250 IMAC/2L Standard
200 .................................................................. ......... : . .... .. : ............................................
150 ....... ................... ..............
-0
C)
100 .......
50
............. ....... .............
...... .... ........ ........
0 --- - - - - - - - - - -1 - - - - �- - ----F - - --r- - --+
U-) LO Ln Lr) LrI tn U') Lr) U') �n
ifl co CD CD 00
CD (D CD <�� Q (2 00 C) CO
CV N N N
N Oj N CV N N N RI Cm N Cm N N N
Figure 46. Predicted Cobalt (pg/L) in Monitoring Well GWA-22D for Model Scenarios 1-3

Predicted Cobalt at GWA-3BRU
- - Scenario 1 - Existing Condition
Scenario 2 - Cap -in -Place
: Scenario 3 - Excavation
..........................
IMAC/2L Standard — —
5 :........ ....... .......... :........ :,,,. :.......:.. :.,.,,,....
4
© 3.........:..........................:..............:........:................. .
0 - -
2 -d—..........:................. Z......:.......:....... .......:
0—r—
Ln to U') Ln Ln Ln +n sn U-) Ln Ln Lr, u') to Ln u)
[O CO O Cq 'S to CO O N 'C fO Lf7 O N 17 [O
G� a) Q O O C O N N C+] N
r N N N CV N N N (m N CV N {V N N
Figure 47. Predicted Cobalt (pg/L) in Monitoring Well GWA-313RU for Model Scenarios 1-3

Predicted Cobalt at GWA-5BRU
180 -
160 -
Scenario 1 - Existing Condition
Scenario 2 - Cap -in -Place
Scenario 3 - Excavation
[MAC12L Standard — —

2.5
2 -1
1.5
.........:.....,,:,.,
0.5 1
0
Predicted Cobalt at GWA-12BRU
u5 U') u; en un u') Ln u) Ln un u') un Ln un
ifl OD Q N IT (D CO Q N cS (4 CO Q N !I,
[O
65 07 CD ID Q Q CV N N N
r T N N N N N N N CV CV CV N N N
Figure 49. Predicted Cobalt (pg/L) in Monitoring Well GWA-12BRU for Model Scenarios 1-3

100
80
A
E 60
E
0
L
V
x 40
a]
20
0
Predicted HexChromium at GWA-3S
Ur, Lr) U') Ln ur) on to U') u') Ur, uI u') u') Ln Ln Lr
ifl M C] N t4' (D CO O N (D CO O N 7 [O
6'� m p Q q 0 0 Cv N N N
r T N N N N N N N RI N N N N N N
Figure 50. Predicted Hexavalent Chromium (pg/L) in Monitoring Well GWA-3S for Model Scenarios 1-3

14
12
4
2
R
Predicted HexChrornium at GWA-4S
Tn u') in in Tj u) u') in U', an Tn un Lrn Lr) uO U�
CO 00 C] N �T co 0) C7 N '7 CO OD O N IT cD
0 Q CD O O N N N N
r N N Cal N N N N N N N N N N N
Figure 51. Predicted Hexavalent Chromium (lag/L) in Monitoring Well GWA-4S for Model Scenarios 1-3

1400 -
1200
1000 -
A
I
E 800
0
L
x 600 -
a]
400 -
200 -
0
Predicted HexChromium at GWA-5S
Ln Ln � � to Ln � Ln � Ln er) LnLr)
00 o IN N CO Q �_ � o � CO
O> 9) Q O U C7 CDiV N N N
T r N N N N N N N N N N N N N N
Figure 52. Predicted Hexavalent Chromium (pg/L) in Monitoring Well GWA-5S for Model Scenarios 1-3

250
200
A
I
E 150
0
L
V
x
a)
= 1v0
50
0
Predicted HexChromium at GWA-4D
u5 Ln r Ln Ln L.n LO U') Ln Vr, u u') Ln Ln Ln u�
ifl M Q N C CO CC] Q CO Q N !I, [O
Q Q Q Q Q CV N N N
r T N CV [N 01i N N ftf RI CV N Ili N N N
Figure 53. Predicted Hexavalent Chromium (pg/L) in Monitoring Well GWA-413 for Model Scenarios 1-3

50
40
I
E 30
0
L
V
x
a)
= 20
0
Li) Li) U')
CO CD O
6 (r C
r r N
Ln
N
O
N
Predicted HexChromum at GWA-9❑
Ln Ln U7 U7 LC) U7 Ln Ln U") Liz LT) Li)
tr LO 00 O N 'R [t7 w o N 'IT c0
0 0 o N N N c
N N N N N N N N N N N N
Figure 54. Predicted Hexavalent Chromium (pg/L) in Monitoring Well GWA-913 for Model Scenarios 1-3

300
250
200
E
E
0 150
x
aw
am
100
50
0
Predicted HexChromium at GWA-22D
u� U') U') va in un isi u3 u'i u') LO un LO u) u1 X-
(D co 0 N 10 CC, 0 N [D
W C3) C7 © O O 0 N N N N
r r N N N N N N N N N N N N N N
Figure 55. Predicted Hexavalent Chromium (Ng/L) in Monitoring Well GWA-22D for Model Scenarios 1-3

50
40
A
F
30
0
L
V
x
Ta)
1 20
LL:
0
Predicted HexChromium at GWA-3BRU
U17 U'7 U') Li] Ln Ln 4:] Uf U') U') Ln Lr] L{7 Lr) LTi 47
CO O N R CO CO p N IT [L7 OO O N If CO
6) [r Cl O q G CD N N N N
r r N N N N N N N N N N N N N N
Figure 56. Predicted Hexavalent Chromium (lag/L) in Monitoring Well GWA-3BRU for Model Scenarios 1-3

600
500 -
400
E
EE 300
L
r�
V
x
I
200
Mien
Predicted HexChromium at GWA-5BRU
i
u'r Ln ur) Un u'a Lr, u') Ln U') uO IS)
to O4 C] N fQ R7 Q CV 'r 'L7 CO C (N � [P
[E3 CTr 0 O O O © CV N N N
r r N N N N N i`J N N N N N N N N
Figure 57. Predicted Hexavalent Chromium (Ng/L) in Monitoring Well GWA-513RU for Model Scenarios 1-3

300000
250000
200000
w 150000
2z
73
CO
100000
50000
0
Predicted Sulfate at GWA-41)
m C C C C C
r N N N CV CV N N
Ln Ln Ln Ln
�t iO CO C N 7 [O
N N N N
N N h3 CV N N N
Figure 58. Predicted Sulfate (Ng/L) in Monitoring Well GWA-413 for Model Scenarios 1-3

250000
200000
150000
i�
CO
100000
50000
0
Predicted Sulfate at GWA-91)
U'T Ln U-) Ln L4) 0 Ln U) LS7 Ln Ln [n Ln LO Ln U)
(0 03 O N R (D 00 O N 12 C] N 7 [0
P7 CT? C3 C7 C? a CDN N N N
r N N N CV CV N N N N CV CV N N N
Figure 59. Predicted Sulfate (Ng/L) in Monitoring Well GWA-913 for Model Scenarios 1-3

Predicted Sulfate at GWA-5BRU
Scenario 1 - Existing Condition
Scenario 2 - Cap -in -Place
Scenario 3 - Excavation
250000.— — — — — — — — — — — — IMACI2L Standard — —
200000 �..................:.......:I..N.........F.......:....... I .....:........:........:.......;.
r
150000
cu -
CO
iDOflDO:......,;........:........:.......: ........................;....".......:........................
50000 -1 ....I ... ........ ............................_..........N,................................
0 I .. �--
uT u') un Ln u') Ln U') u') u') Ln Ln rn U') uO uO u)
(D 00 O N R (D 00 O N R (O 00 O N 7 [O
p7 m a O CD C N N N N
r N N N CV CV N N N N N CV N N N
Figure 60. Predicted Sulfate (pg/L) in Monitoring Well GWA-5BRU for Model Scenarios 1-3

450000
400000
350000
300000
i
250000
d]
c[3
200000
J
150000
100000
50000
0
Predicted Sulfate at GWA-9BR
(0 trJ O N R ED 00 O N O N 7 U]
9) CT, C3 Q C? 0 C N N N N
r N N N CV CV N CL N N N CV N N N
Figure 61. Predicted Sulfate (pg/L) in Monitoring Well GWA-9BR for Model Scenarios 1-3

s
E 6
0
tea
4
0
Predicted Vanadium at GWA-3S
If! u") u') Ln Ln Ln 4n u') Ln 4n u') Ln u') 1n In u)
rd7 00 o N tr cn CO 0 N 'R [n 00 O N rn
tr C O q O CD N N N N
r r N N N N N N N N N N N N N N
Figure 62. Predicted Vanadium (pg/L) in Monitoring Well GWA-3S for Model Scenarios 1-3

12
8
E
8
0
tea
4
2
0
Predicted Vanadium at GWA-4S
Ln u') u') u) In Ln U') U') U') 4n Ln Ln u') Xn In un
ca m o N tr CO CO a N er n 00 o N IT CO
rn rn Q o q a o N N N N
r r N N N N N N N N N N N N N N
Figure 63. Predicted Vanadium (pg/L) in Monitoring Well GWA-4S for Model Scenarios 1-3

20
^ 15
E
0
10
5
0
Predicted Vanadium at GWA-5S
to rn u') Ln Ln Ln Ln in In Ln Ln Ln Ln Lr, lx� Ln
Cp 00 O N er cn CO 0 N '4' (n 00 O N et CO
O1 4s C O q CD CD N N N N
e— N N N N N N N N N N N N N N
Figure 64. Predicted Vanadium (pg/L) in Monitoring Well GWA-5S for Model Scenarios 1-3

Soo
400
0)
3©❑
E
c1
c
a1
> 200
1TI
0
Predicted Vanadium at GWA-9S
Scenario 1 Existing Condition
Scenario 2 - Cap -in -Place
Scenario 3 - Excavation
IMAC/2L Standard — —
w 03 0 CQ R i0 w C7 C7 N 2
6> 6� 0 0 O 0 4 N N N N
r r N N N N N N N N N N N N N N
Figure 65. Predicted Vanadium (Ng/L) in Monitoring Well GWA-9S for Model Scenarios 1-3

Predicted Vanadium at GWA-12S
5 ........ ......
Scenario 1 - Existing Condition
Scenario 2 - Cap -in -Place
Scenario 3 - Excavation
NAC/2L Standard
4 ...................................... ........... .......................................... ...........
3
.............. ............ ............ ....... .................. ........... ....... ........
F
CU2
................................................. ........... ......... ....................... ....... .........................
>
0
...................... ..................... ....... .... ....... I ......................... ....... ..
Ln U') U') U') Ln U') U') U') U') U') Lf') LO U') U') Ln LI)
CO CO CD CV rp (D CO C2, �O
CD It
a) C� CD Q CQ N N C\j
N N N N N N N N (%] CV N N N N
Figure 66. Predicted Vanadium (pg/L) in Monitoring Well GWA-12S for Model Scenarios 1-3

40
35
30
25
E
0 20
oz
15
IM
M
0
Predicted Vanadium at GWA-4D
Scenario 1 - Existing Condition
Scenario 2 - Cap -in -Place
Scenario 3 - Excavation
IMAC/2L Standard - -
-4. ....:.......... .... si i'.....•........•........................................I.......... l...................,..,.,..4-
:
to Ln in Ln Un U') u') Ln U') U') U') ui Ln Ln V� Lrr
m aQ a N v cp CO o_ N v (0 o0 o N �r cD
0 B) Q Q Q Q O N N N N
+- N N. N N N N N N N N N N N N
Figure 67. Predicted Vanadium (Ng/L) in Monitoring Well GWA-413 for Model Scenarios 1-3

3500
3000
2500
2000
E
0
C[3
CZ 1500
1000
500
0
Predicted Vanadium at GWA-9D
Scenario 1 - Existing Condition
Scenario 2 - Cap -in -Place
Scenario 3 - Excavation
]MAC/2L Standard — —
U) U') Ln Ui U] U) U') U) N U) U) U') LO LO L{7 lt7
0 Lt] O M a (0 OD 0 M (D av 0 M It (L)
ff+ 01 O CJ :7 C) 0 SV M N N
r N N N N N N N N N N N N N N
Figure 68. Predicted Vanadium (Ng/L) in Monitoring Well GWA-913 for Model Scenarios 1-3

300
250
200
E
150
tea
100
50
0
Predicted Vanadium at GWA-22D
u') u u') Ln Ln Ln U) u Ln r u u') Ln Ln Ln u�
ifl 0p q CV C CO 00 O N �S C[) CO CDN 7 (f7
05 6? q q CD q q CV N N N
r T N N N N N N N RI CV Ti I�j N CQ N
Figure 69. Predicted Vanadium (pg/L) in Monitoring Well GWA-22D for Model Scenarios 1-3

Predicted Vanadium at GWA-3BRU
12 -1 ...
10 - -
8
E
a
0
tea
4 —1 ../...... .X....... N .. ......................:.......I...... ........ ,...
Scenario 1 - Existing Condition
Scenario 2 - Cap -in -Place
Scenario 3 - Excavation
IMAC/2L Standard — —
2 -1. - ... /... . ...,I . . ...... . .......N,; ,.... _ ......,�`... _ ..... - ...., _ ..... _ ...., _ ..... - ...... .
If! LIs in Ln U] Lis Ln Ln Lr) Ln U') Ln Lis Ln Ln Ln
rd7 00 o N tr CO CO o N '4' Cn ao o N 'If iD
tQ CD C7 C7 P N N N N
r r N N N N N N N N N N N N N N
Figure 70. Predicted Vanadium (pg/L) in Monitoring Well GWA-3BRU for Model Scenarios 1-3

40
35
30
3a
25
E
0 20
C
tea
15
10
5
0
Predicted Vanadium at GWA-5BRU
Scenario 1 - Existing Condition
Scenario 2 - Cap -in -Place
Scenario 3 - Excavation
[MAC/2L Standard — —
u') u') Ur, Ur, Ln Ln u') U') 4n ua u') u') u') u)
co 00 O N R cn CO N 4 n w o N c1 SO
4 CD C7 C7 P N N N N
r r N N N N N N N N N N N N N N
Figure 71. Predicted Vanadium (pg/L) in Monitoring Well GWA-5BRU for Model Scenarios 1-3

Predicted Vanadium at GWA-9BR
90
so
70
C
60
E
50
i
40
30
10
o- - - — , . .
u') U') Ln sn Ln in u7 Ln Ln un Ln T)
O N d' 0 OD o N Tt LO a0 0
65 N N © 4 CV fV N fL N N
Figure 72. Predicted Vanadium (lag/L) in Monitoring Well GWA-9BR for Model Scenarios 1-3
Ln Ln
N et
N N N

Predicted Vanadium at GWA-12BRU
5 ...., .. . .
4.......................................... I ....... I .................................
E 3
0
as
2 ,.,,.....,..,. ....I .........................
t-I............................................. I
J
U7 U7 u7 Ln
w CO o [y
1 65 Q O
r N N
T
Ln In
rp cn
O G
N CV
U')
Ln
Lr)
4n
un
Lr)
+n
u')
LO u)
CO
O
N
[a
CDN
It[O
4
N
N
Cj N
CV
N
N
N
N
CV
N
CJ
N N
Figure 73. Predicted Vanadium (lag/L) in Monitoring Well GWA-12BRU for Model Scenarios 1-3

Figure 74. Initial (2015) Antimony Concentrations (fag/L) in the Shallow Groundwater Zone

Figure 75. Initial (2015) Antimony Concentrations (Ng/L) in the Deep Groundwater Zone

Figure 76. Initial (2015) Antimony Concentrations (Ng/L) in the Bedrock Groundwater Zone

1500
500
160
40
10
3
� 1
rI
4
I J
Y pOt6t!.�i�0.
Ali
O
p
ACTIVE
ASH BASIN
PRIMARY CELL ASH A
STORAGE
�y� r.
Vol
a
i
r
ACTIVE
ASH BASItd
OLD PRIMARY AGTi+JE
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Figure 77. "Existing" Scenario 1 - 2115 Predicted Antimony (lag/L) in the Shallow Groundwater Zone

Figure 78. "Existing" Scenario 1 - 2115 Predicted Antimony (Ng/L) in the Deep Groundwater Zone

Figure 79. "Existing" Scenario 1 - 2115 Predicted Antimony (pg/L) in the Bedrock Groundwater Zone

Figure 80. "Cap -In -Place" Scenario 2 - 2115 Predicted Antimony (lag/L) in the Shallow Groundwater Zone

Figure 81. "Cap -In -Place" Scenario 2 - 2115 Predicted Antimony (pg/L) in the Deep Groundwater Zone

Figure 82. "Cap -In -Place" Scenario 2 - 2115 Predicted Antimony (pg/L) in the Bedrock Groundwater Zone

Figure 83. "Excavate" Scenario 3 - 2115 Predicted Antimony (Ng/L) in the Shallow Groundwater Zone

Figure 84. "Excavate" Scenario 3 - 2115 Predicted Antimony (Ng/L) in the Deep Groundwater Zone

Figure 85. "Excavate" Scenario 3 - 2115 Predicted Antimony (Pg/L) in the Bedrock Groundwater Zone

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40
20
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Figure 86. Initial (2015) Boron Concentrations (Ng/L) in the Shallow Groundwater Zone

Figure 87. Initial (2015) Boron Concentrations (pg/L) in the Deep Groundwater Zone

Figure 88. Initial (2015) Boron Concentrations (lag/L) in the Bedrock Groundwater Zone

Figure 89. "Existing" Scenario 1 - 2115 Predicted Boron (pg/L) in the Shallow Groundwater Zone

Figure 90. "Existing" Scenario 1 - 2115 Predicted Boron (Ng/L) in the Deep Groundwater Zone

Figure 91. "Existing" Scenario 1 - 2115 Predicted Boron (pg/L) in the Bedrock Groundwater Zone

Figure 92. "Cap -In -Place" Scenario 2 - 2115 Predicted Boron (pg/L) in the Shallow Groundwater Zone

Figure 93. "Cap -In -Place" Scenario 2 - 2115 Predicted Boron (pg/L) in the Shallow Groundwater Zone

Figure 94. "Cap -In -Place" Scenario 2 - 2115 Predicted Boron (pg/L) in the Bedrock Groundwater Zone

Figure 95. "Excavate" Scenario 3 - 2115 Predicted Boron (jig/L) in the Shallow Groundwater Zone

Figure 96. "Excavate" Scenario 3 - 2115 Predicted Boron (Ng/L) in the Deep Groundwater Zone

Figure 97. "Excavate" Scenario 3 - 2115 Predicted Boron (Ng/L) in the Bedrock Groundwater Zone

Figure 98. Initial (2015) Chromium Concentrations (Ng/L) in the Shallow Groundwater Zone

Figure 99. Initial (2015) Chromium Concentrations (pg/L) in the Deep Groundwater Zone

Figure 100. Initial (2015) Chromium Concentrations (Ng/L) in the Bedrock Groundwater Zone

Figure 101. "Existing" Scenario 1 - 2115 Predicted Chromium (Ng/L) in the Shallow Groundwater Zone

Figure 102. "Existing" Scenario 1 - 2115 Predicted Chromium (Ng/L) in the Deep Groundwater Zone

Figure 103. "Existing" Scenario 1 - 2115 Predicted Chromium (pg/L) in the Bedrock Groundwater Zone

Figure 104. "Cap -In -Place" Scenario 2 - 2115 Predicted Chromium (lag/L) in the Shallow Groundwater Zone

Figure 105. "Cap -In -Place" Scenario 2 - 2115 Predicted Chromium (pg/L) in the Deep Groundwater Zone

Figure 106. "Cap -In -Place" Scenario 2 - 2115 Predicted Chromium (pg/L) in the Bedrock Groundwater Zone

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Figure 107. "Excavate" Scenario 3 - 2115 Predicted Chromium (Ng/L) in the Shallow Groundwater Zone

Figure 108. "Excavate" Scenario 3 - 2115 Predicted Chromium (pg/L) in the Deep Groundwater Zone

Figure 109. "Excavate" Scenario 3 - 2115 Predicted Chromium (Ng/L) in the Bedrock Groundwater Zone

Figure 110. Initial (2015) Cobalt Concentrations (Ng/L) in the Shallow Groundwater Zone

Figure 111. Initial (2015) Cobalt Concentrations (pg/L) in the Deep Groundwater Zone

Figure 112. Initial (2015) Cobalt Concentrations (pg/L) in the Bedrock Groundwater Zone

Figure 113. "Existing" Scenario 1 - 2115 Predicted Cobalt (Ng/L) in the Shallow Groundwater Zone

Figure 114. "Existing" Scenario 1 - 2115 Predicted Cobalt (pg/L) in the Deep Groundwater Zone

Figure 115. "Existing" Scenario 1 - 2115 Predicted Cobalt (Ng/L) in the Bedrock Groundwater Zone

Figure 116. "Cap -In -Place" Scenario 2 - 2115 Predicted Cobalt (pg/L) in the Shallow Groundwater Zone

Figure 117. "Cap -In -Place" Scenario 2 - 2115 Predicted Cobalt (pg/L) in the Deep Groundwater Zone

Figure 118."Cap-In-Place" Scenario 2 - 2115 Predicted Cobalt (lag/L) in the Bedrock Groundwater Zone

Figure 119. "Excavate" Scenario 3 - 2115 Predicted Cobalt (pg/L) in the Shallow Groundwater Zone

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Figure 120. "Excavate" Scenario 3 - 2115 Predicted Cobalt (Ng/L) in the Deep Groundwater Zone

Figure 121. "Excavate" Scenario 3 - 2115 Predicted Cobalt (Ng/L) in the Bedrock Groundwater Zone

Figure 122. Initial (2015) Hexavalent Chromium Concentrations (Ng/L) in the Shallow Groundwater Zone

Figure 123. Initial (2015) Hexavalent Chromium Concentrations (pg/L) in the Deep Groundwater Zone

Figure 124. Initial (2015) Hexavalent Chromium Concentrations (lag/L) in the Bedrock Groundwater Zone

Figure 125. "Existing" Scenario 1 - 2115 Predicted Hexavalent Chromium (Ng/L) in the Shallow Groundwater Zone

Figure 126. "Existing" Scenario 1 - 2115 Predicted Hexavalent Chromium (Ng/L) in the Deep Groundwater Zone

Figure 127. "Existing" Scenario 1 - 2115 Predicted Hexavalent Chromium (Ng/L) in the Bedrock Groundwater Zone

Figure 128. "Cap -In -Place" Scenario 2 - 2115 Predicted Hexavalent Chromium (Ng/L) in the Shallow Groundwater Zoned

Figure 129. "Cap -In -Place" Scenario 2 - 2115 Predicted Hexavalent Chromium (pg/L) in the Deep Groundwater Zone

Figure 130. "Cap -In -Place" Scenario 2 - 2115 Predicted Hexavalent Chromium (Ng/L) in the Bedrock Groundwater Zone

Figure 131. "Excavate" Scenario 3 - 2115 Predicted Hexavalent Chromium (Ng/L) in the Shallow Groundwater Zone

Figure 132. "Excavate" Scenario 3 - 2115 Predicted Hexavalent Chromium (pg/L) in the Deep Groundwater Zone

Figure 133. "Excavate" Scenario 3 - 2115 Predicted Hexavalent Chromium (pg/L) in the Bedrock Groundwater Zone

Figure 134. Initial (2015) Sulfate Concentrations (lag/L) in the Shallow Groundwater Zone

Figure 135. Initial (2015) Sulfate Concentrations (lag/L) in the Deep Groundwater Zone

Figure 136. Initial (2015) Sulfate Concentrations (pg/L) in the Bedrock Groundwater Zone

Figure 137. "Existing" Scenario 1 - 2115 Predicted Sulfate (Ng/L) in the Shallow Groundwater Zone

Figure 138. "Existing" Scenario 1 - 2115 Predicted Sulfate (pg/L) in the Deep Groundwater Zone

Figure 139. "Existing" Scenario 1 - 2115 Predicted Sulfate (Ng/L) in the Bedrock Groundwater Zone

Figure 140. "Cap -In -Place" Scenario 2 - 2115 Predicted Sulfate (pg/L) in the Shallow Groundwater Zone

Figure 141. "Cap -In -Place" Scenario 2 - 2115 Predicted Sulfate (pg/L) in the Deep Groundwater Zone

Figure 142. "Cap -In -Place" Scenario 2 - 2115 Predicted Sulfate (Ng/L) in the Bedrock Groundwater Zone

Figure 143. "Excavate" Scenario 3 - 2115 Predicted Sulfate (Ng/L) in the Shallow Groundwater Zone

Figure 144. "Excavate" Scenario 3 - 2115 Predicted Sulfate (fag/L) in the Deep Groundwater Zone

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Figure 145. "Excavate" Scenario 3 - 2115 Predicted Sulfate (Ng/L) in the Bedrock Groundwater Zone

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Figure 146. Initial (2015) Vanadium Concentrations (Ng/L) in the Shallow Groundwater Zone

Figure 147. Initial (2015) Vanadium Concentrations (lag/L) in the Deep Groundwater Zone

Figure 148. Initial (2015) Vanadium Concentrations (Ng/L) in the Bedrock Groundwater Zone

Figure 149. "Existing" Scenario 1 - 2115 Predicted Vanadium (Ng/L) in the Shallow Groundwater Zone

Figure 150. "Existing" Scenario 1 - 2115 Predicted Vanadium (Ng/L) in the Deep Groundwater Zone

Figure 151. "Existing" Scenario 1 - 2115 Predicted Vanadium (Ng/L) in the Bedrock Groundwater Zone

Figure 152. "Cap -In -Place" Scenario 2 - 2115 Predicted Vanadium (pg/L) in the Shallow Groundwater Zone

Figure 153. "Cap -In -Place" Scenario 2 - 2115 Predicted Vanadium (pg/L) in the Deep Groundwater Zone

Figure 154. "Cap -In -Place" Scenario 2 - 2115 Predicted Vanadium (pg/L) in the Bedrock Groundwater Zone

Figure 155. "Excavate" Scenario 3 - 2115 Predicted Vanadium (Ng/L) in the Shallow Groundwater Zone

Figure 156. "Excavate" Scenario 3 - 2115 Predicted Vanadium (pg/L) in the Deep Groundwater Zone

Figure 157. "Excavate" Scenario 3 - 2115 Predicted Vanadium (Ng/L) in the Bedrock Groundwater Zone