BIOPLUME II Introduction to Solution Methods and Model Mechanics

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BIOPLUME IIIntroduction to Solution Methods and
Model Mechanics
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What does it do?

• Two dimensional finite difference model for
  simulating natural attenuation due to
• advection
• dispersion
• sorption
• biodegradation

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How Does BPIII Solve Equations?

• Contaminant transport solved using the Method of
  Characteristics
• Particles travel along Characteristic lines
  determined by flow solution.
• Particles carry mass
• Advection solved via particle movement
• Dispersion solved explicitly
• Reaction solved explicitly
• First order decay
• Instantaneous Biodegradation

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Particle Movement
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Limitations/Assumptions

• Darcys Law is valid
• Porosity and hydraulic conductivity constant in
  time, porosity constant in space
• Fluid density, viscosity and temperature have no
  effect on flow velocity
• Reactions do not affect fluid or aquifer
  properties
• Ionic and molecular diffusion negligible
• Vertical variations in head/concentration
  negligible
• Homogeneous, isotropic longitudinal and
  transverse dispersivity

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Limitations of Biodegradation

• No selective or competitive biodegradation of
  hydrocarbons (lumped hydrocarbons)
• Conceptual model of biodegradation is a
  simplification of the complex biologically
  mediated redox reactions that occur in the
  subsurface

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BIOPLUME II Flowchart
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HOW TO SET UP A MODEL

• 1. Data Collection Analysis
• 2. Modeling Scale
• 3. Discretization
• 4. Boundary Conditions
• 5. Parameter Estimation
• 6. Calibration
• 7. Sensitivity Analysis
• 8. Error Estimation
• 9. Prediction

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SOURCE DATA

• Mass of contaminant
• Q, C0
• Discrete vs. Continuous
• Nature of contaminant
• Chemical stability
• Biological stability
• Adsorption

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PARAMETER ESTIMATION

• 1. Porosity
• 2. Dispersivity
• 3. Storage coefficients
• 4. Hydraulic conductivity
• 5. Thickness of unit
• 6. Recharge rates

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REGIONAL SCALE - QUANTITATIVE

• Aquifer characteristics
• Background gradients
• Geology
• Recharge sources

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LOCAL SCALE - WATER QUALITY

• Site history
• Site characterization
• Source definition
• Nature of contamination
• Plume delineation

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MOC TIMING PARAMETERS

• Total Simulation Time
• 1st pumping period
  2nd
• NPMP 2
• For Each Pumping Period
• PINT pumping period in yrs
• NTIM of time steps in pumping period

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MOC BOUNDARY CONDITIONS

• Two types
• Constant Head
• Water Table constant
• Constant Flux
• Flow rate Q
• Concentration C0

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MOC BOUNDARY CONDITIONSSpecifications of NCODES

• For Each Code in NOEID map
• LEAKANCE (s-1)
• vertical hyd. conduct. / thickness
• CONCENTRATION OF CONTAMINANT
• RECHARGE RATE (ft/s)
• NOTE
• For constant head cells set LEAKANCE to 1.0

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MOC SOURCE DEFINITION

• Injection well
• Flow rate - Q
• Concentration - C0
• Constant Head Cell
• CC0
• Recharge Cell
• Flow rate - Q
• Concentration - C0

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PHYSICAL AQUIFER CHARACTERISTICS

• 1. Transmissivity (ft2/s) VPRM
• 2. Thickness (ft) THCK
• 3. Dispersivity (ft)
• Longitudinal BETA
• Ratio DLTRAT Txx/Tyy
• 4. Porosity POROS
• 5. Storativity S
• NOTE
• For transient problems
• TIMX increment multiplier
• TINIT size of initial time step

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MOC REACTION PARAMETERS

• NREACT
• Flag to instruct MOC to expect reaction data
• 0 - no reactions
• 1 - reactions taking place
• expect card 4 free format
• Two types of reaction
• RETARDATION
• KD - Distribution coefficient
• RHOB - Bulk density
• RADIOACTIVE DECAY
• THALF - Half life of solute

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INPUT PARAMETERS AFFECTING ACCURACY FOR HYDRAULIC
CALCULATIONS

• ITMAX
• Maximum allowable number of iterations 100-200
• Increase ITMAX if hydraulic mass balance error is
  gt 1
• NITP
• Number of iteration parameters
• USE 7
• TOL
• Convergence criteria lt0.01
• Decrease TOL to get less hydraulic mass balance
  error

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PARAMETERS AFFECTING ACCURACY OF TRANSPORT

• NPTPND - Number of particles in a cell
• NPMAX - Maximum number of particles
• NX NY NPTPND

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STABILITY CRITERIA FOR MOC

• MOC may require dividing NTIM or PINT into
  smaller move time steps
• ?t minimum of
• Dispersion
• Mixing
• Advection

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INPUT PARAMETERS AFFECTING STABILITY OF MOC

• CELDIS - max distance per move
• If CELDIS lt space between particles MOC will
  oscillate for N yrs BUT gives smallest Mass
  Balance errors for TgtN
• If CELDIS Stability Criteria DO a sensitivity
  analysis on CELDIS
• NPTPND - initial of particles
• Accuracy of MOC directly proportional to NPTPND
• Runtime inversely proportional to NPTPND
• RULE OF THUMB
• Initially set NPTPND4 or 5 and CELDIS0.75 or 1
• For final runs use NPTPND9 and CELDIS0.5

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Output control

• NPNTMV
• Number of particle moves after which output is
  requested. Use 0 to print at end of time steps
• NPNTVL
• Printing velocities
• 0 - do not print
• 1 - print for first time step
• 2 - print for all time steps

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Output control (cont.)

• NPNTD
• Print dispersion equation coefficients
• NPDELC
• Print changes in concentration
• NPNCHV
• Do not use this option. Always set to 0. It is
  used to request cards to be punched.