The PHAST 3D Reactive-The PHAST 3D Reactive-Transport SimulatorTransport Simulator

David Parkhurst, Ken Kipp, and David Parkhurst, Ken Kipp, and Scott CharltonScott Charlton

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AgendaAgenda

Introduction to PHASTIntroduction to PHAST Review of geochemical reactionsReview of geochemical reactions Phast4Windows Phast4Windows

– Flow modeling exerciseFlow modeling exercise– Reactive-transport modeling exerciseReactive-transport modeling exercise

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3D Reactive-Transport 3D Reactive-Transport ModelingModeling

Three simultaneous processesThree simultaneous processes– FlowFlow– TransportTransport– Chemical reactionChemical reaction

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PHASTPHAST HST3D—Flow and transportHST3D—Flow and transport

PHREEQC—ChemistryPHREEQC—Chemistry

Operator splitting—Sequential Non-Operator splitting—Sequential Non-

Iterative ApproachIterative Approach

PHT3D is a 3D reactive transport PHT3D is a 3D reactive transport

model built on MODFLOW, MT3DMS, model built on MODFLOW, MT3DMS,

and PHREEQCand PHREEQC

Chemistry

Transport

Flow

Chemistry

Transport

Flow

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Flow and TransportFlow and Transport

Constant temperatureConstant temperature Constant densityConstant density Single phase Single phase Saturated confined or unconfined flowSaturated confined or unconfined flow Point-distributed finite-difference gridPoint-distributed finite-difference grid Boundary conditions Boundary conditions

– Specified, leaky, flux, rivers, drains, wellsSpecified, leaky, flux, rivers, drains, wells

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Grid ElementGrid Element

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Grid CellGrid Cell

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Full Cell Has Parts of 8 ElementsFull Cell Has Parts of 8 Elements

Cell Properties do not change abruptly Cell Properties do not change abruptly – Media properties weighted by volumeMedia properties weighted by volume– Conductances weighted by facial areaConductances weighted by facial area

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ZonesZones

Box—Rectangular brickBox—Rectangular brick Wedge—Right triangular wedgeWedge—Right triangular wedge PrismPrism

– PerimeterPerimeterArc shapeArc shapeXYZ fileXYZ filepointspoints

– Top, BottomTop, BottomArc rasterArc rasterArc shape + attributeArc shape + attributeXYZ fileXYZ filePointsPoints

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PerimeterPerimeter

TopTop

BottomBottom

PrismPrism

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Interpolation for Top and BottomInterpolation for Top and Bottom XYZ Data are treated as scattered pointsXYZ Data are treated as scattered points Natural neighbor interpolation (NNI) is Natural neighbor interpolation (NNI) is

used if possibleused if possible– Defines a continuous surface except at data Defines a continuous surface except at data

pointspoints– NNI is not simply the closest neighborNNI is not simply the closest neighbor– Area weights by nearest pointsArea weights by nearest points

Uses closest neighbor interpolation (CNI) if Uses closest neighbor interpolation (CNI) if NNI failsNNI fails– Not continuousNot continuous– Used outside convex hullUsed outside convex hull

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Two Coordinate SystemsTwo Coordinate Systems

Map—State plane, UTMMap—State plane, UTM Grid—Local coordinate systemGrid—Local coordinate system Not quite finishedNot quite finished Today, map = gridToday, map = grid

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Assigning Properties to a ZoneAssigning Properties to a Zone

ConstantConstant Linear in X, Y, or Z directionLinear in X, Y, or Z direction Points—Values at set of X,Y,Z pointsPoints—Values at set of X,Y,Z points XYZ File—Values at set of X,Y,Z XYZ File—Values at set of X,Y,Z

pointspoints XYZT File—Boundary conditions onlyXYZT File—Boundary conditions only

– X,Y,Z,T,P: property at location and timeX,Y,Z,T,P: property at location and time

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3D Interpolation from Points3D Interpolation from Points

Properties are assigned from the Properties are assigned from the closest of the set of pointsclosest of the set of points

Produces a volume with constant Produces a volume with constant property around each pointproperty around each point

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Spatially Distributed Properties Are Spatially Distributed Properties Are Overlayed in Zone SequenceOverlayed in Zone Sequence

Property P defined Property P defined by green followed by green followed by brown zoneby brown zone

Property P defined Property P defined by brown followed by brown followed by green zoneby green zone

P = 10P = 20

P = 10 P = 20

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ZonesZones MediaMedia Initial conditionsInitial conditions Boundary conditionsBoundary conditions Zone flowsZone flows

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Media PropertiesMedia Properties ActiveActive KxKx KyKy KzKz PorosityPorosity Specific storageSpecific storage Longitudinal dispersivityLongitudinal dispersivity Horizontal component transverse dispersivityHorizontal component transverse dispersivity Vertical component transverse dispersivityVertical component transverse dispersivity

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Head ICHead IC

Define head distribution for zone Define head distribution for zone – ConstantConstant– Linear in X, Y, or ZLinear in X, Y, or Z– PointsPoints– XYZ file with pointsXYZ file with points

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Specified Head BCSpecified Head BC

Some grid dependence because a Some grid dependence because a specified head applies to entire cellspecified head applies to entire cell

Time-dependent valuesTime-dependent values– HeadHead– Solution numberSolution number

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Leaky (Head dependent) BC Leaky (Head dependent) BC Applies only over area defined by zone Applies only over area defined by zone

(partial cell faces)(partial cell faces) Applies only to exterior facesApplies only to exterior faces Z face—water goes to first active cell or Z face—water goes to first active cell or

water tablewater table ParametersParameters

– ThicknessThickness– Hydraulic conductivityHydraulic conductivity

Time-dependent valuesTime-dependent values– HeadHead– Solution numberSolution number

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Flux BCFlux BC

Applies only to area of Applies only to area of cell face intersected by cell face intersected by the zonethe zone

Time-dependent valuesTime-dependent values– FluxFlux– SolutionSolution

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Overlapping BCOverlapping BC

Duplicate flux areas are removedDuplicate flux areas are removed Duplicate leaky areas are removedDuplicate leaky areas are removed Leaky and flux can coexist on a cell Leaky and flux can coexist on a cell

face face Neither Leaky nor flux can coexist Neither Leaky nor flux can coexist

with specified headwith specified head– Last defined takes precedence Last defined takes precedence

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Rivers & DrainsRivers & Drains Series of X,Y pointsSeries of X,Y points ParametersParameters

– WidthWidth– Bed hydraulic conductivityBed hydraulic conductivity– Bed thicknessBed thickness– Elevation of bedElevation of bed

Time-dependent values (Rivers only)Time-dependent values (Rivers only)– HeadHead– Solution Solution

Parameters and time-dependent values Parameters and time-dependent values – Must define for first and last pointMust define for first and last point– If not defined at intermediate points, If not defined at intermediate points,

interpolation by river distanceinterpolation by river distance

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River and Drain User DefinitionRiver and Drain User Definition

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River and Drain ProcessingRiver and Drain Processing

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WellsWells

X, Y locationX, Y location ParametersParameters

– DiameterDiameter– AllocationAllocation– Open intervalsOpen intervals

Time-dependent parametersTime-dependent parameters– Pumping/injection ratePumping/injection rate– Solution numberSolution number

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PHAST (PHREEQC) ChemistryPHAST (PHREEQC) Chemistry

Aqueous modelsAqueous models– WateqWateq– LLNLLLNL– PitzerPitzer– SIT (Specific ion Interaction Theory)SIT (Specific ion Interaction Theory)

ReactantsReactants– Mineral equilibriumMineral equilibrium– Surface complexationSurface complexation– Ion exchangeIon exchange– Solid solutionsSolid solutions– Kinetic reactionsKinetic reactions

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Transport and ChemistryTransport and Chemistry

Flow and transport data file (.trans.dat)Flow and transport data file (.trans.dat) Chemistry data file (.chem.dat)Chemistry data file (.chem.dat)

– SolutionsSolutions– Mineral equilibriumMineral equilibrium– Surface complexationSurface complexation– Ion exchangeIon exchange– Solid solutionsSolid solutions

– Kinetic reactionsKinetic reactions

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Mineral Assemblage in .chem.datMineral Assemblage in .chem.dat

EQUILIBRIUM_PHASES 11EQUILIBRIUM_PHASES 11

Calcite Calcite 0 0 0.30.3

DolomiteDolomite 00 1.21.2

Identified by an integer (11)Identified by an integer (11) Apply to a zoneApply to a zone

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Chemistry-Transport ConnectionsChemistry-Transport Connections ID numbers for reactants in .chem.dat ID numbers for reactants in .chem.dat

– SOLUTIONSSOLUTIONS– EQUILIBRIUM_PHASES—Minerals and gases)EQUILIBRIUM_PHASES—Minerals and gases)– SURFACE—Surface complexation sitesSURFACE—Surface complexation sites– EXCHANGE—Ion exchangersEXCHANGE—Ion exchangers– SOLID_SOLUTIONS—Solid solutionsSOLID_SOLUTIONS—Solid solutions– KINETICS—Kinetic reactionsKINETICS—Kinetic reactions

Used in .trans.dat fileUsed in .trans.dat file– CHEMISTRY_IC (all reactants)CHEMISTRY_IC (all reactants)– Boundary conditions (solutions only)Boundary conditions (solutions only)

Specified headSpecified head LeakyLeaky FluxFlux RiverRiver WellWell

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ParallelizationParallelization Single processorSingle processor: :

Flow and transportFlow and transport Multiple processorsMultiple processors: :

ChemistryChemistry Data passed using MPI Data passed using MPI 10-30 processors10-30 processors Up to 500,000? nodesUp to 500,000? nodes Hours of CPUHours of CPU Transport

Flow

Transport

Flow

Chemistry

Cells Cells Cells CellsCells

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New ParallelizationNew Parallelization Single Single processor:processor:

FlowFlow

Multiple Multiple processorsprocessors: :

TransportTransport

Multiple Multiple processorsprocessors: :

ChemistryChemistry

Flow

Transport

Flow

Chemistry

Cells Cells Cells CellsCells

Na Cl H +/-O

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Arsenic in the Arsenic in the Central Oklahoma Central Oklahoma

AquiferAquifer Arsenic mostly in confined Arsenic mostly in confined

part of aquiferpart of aquifer Arsenic associated with high Arsenic associated with high

pHpH Flow: Flow:

– UnconfinedUnconfined– ConfinedConfined– UnconfinedUnconfined

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Geochemical Reactions Geochemical Reactions Brine initially fills the aquiferBrine initially fills the aquifer Calcite and dolomite equilibriumCalcite and dolomite equilibrium Cation exchange Cation exchange

– 2NaX + Ca2NaX + Ca+2+2 = CaX = CaX22 + 2Na + 2Na++

– 2NaX + Mg2NaX + Mg+2+2 = MgX = MgX22 + 2Na + 2Na++

Surface complexationSurface complexationHfo-HAsO4Hfo-HAsO4-- + OH + OH-- = HfoOH + HAsO4 = HfoOH + HAsO4-2-2

Desorption at pH > 8.5Desorption at pH > 8.5

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Arsenic Concentrations over Geologic Arsenic Concentrations over Geologic TimeTime

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PHASTPHAST PHAST is a 3D reactive-transport modelPHAST is a 3D reactive-transport model Field-scale problems with limitationsField-scale problems with limitations Data requirements Data requirements

– Field—Aquifer tests, tracer tests, logging, chemical Field—Aquifer tests, tracer tests, logging, chemical samplessamples

– Laboratory—column experiments, extractions, Laboratory—column experiments, extractions, mineralogymineralogy

Modeling results Modeling results – Understanding natural systemsUnderstanding natural systems– Designing engineered Designing engineered – Predicting long-term effectsPredicting long-term effects

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