CONTAMINANT TRANSPORT MECHANISMS

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• CONTAMINANT TRANSPORT MECHANISMS

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ADVECTION PROCESSES

• Seepage velocity
• K hydraulic conductivity
• n effective porosity
• h hydraulic head
• Advective flux

h
h1
h2
vx
x1
x
X2
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DIFFUSION AND DISPERSION PROCESSES

• Ficks first law
• fx mass flux M/L2/T
• Dd diffusion coefficient L2/T
• h hydraulic head

C
C1
C2
fx
x1
x
X2
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STOCHASTIC SIMULATION OF ADVECTION DIFFUSION
PROCESSES

• Use a large number of particles
• Predict their position using
• Determine their position and
• distribution at ttfinal
• v0.15 m/h
• Dd0.0034 m2/h

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ADVECTION DISPERSION EQUATION FOR SOLUTE TRANSPORT
z

• Mass conservation
• Min-MoutAccumulation

dz
y
dx
dy
x
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ADVECTION DISPERSION EQUATION FOR SOLUTE
TRANSPORT (ctd)

• Complete formulation
• 1-D formulation
• Analytical solutions exist sometimes for both
  complete and 1-D formulations (e.g. BIOCHLOR)

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ADSORPTION EFFECTS

• Sorption
• association of a contaminant with a solid
  material
• adsorption association with the surface of the
  solid
• absorption association within the solid
• S f(C) the amount of absorbed contaminant is a
  function of C
• SKdCb
• The transport equation becomes
• If b1 then

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ADSORPTION AND FIRST-ORDER DECAY EFFECTS

• First order decay
• Transport and adsorption
• The combination of the two equations yields
• where R is the retardation factor

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ADSORPTION ISOTHERM

• Freundlich adsorption isotherm
• SKdCb
• Consider a simple
• experimental setup
• L1cm
• Darcy flux q0.27cm/h
• Porosity n0.3
• Cin is measured and given
• Cout is measured and given

q, Cout
q,Cin
L1cm
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ANALYTICAL SOLUTION (2-D CASE)

• Hypotheses
• no advection in y-direction
• constant vx velocity
• conservative substance
• pulse source
• Example
• 2 wells ( (3.7, 0.2), (4.9,-2.8) )
• tracer is injected at (0,0)
• determine vx, Dx, Dy,

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ANALYTICAL SOLUTION (2-D CASE)

• Solution
• Use the Excel Solver (obviously) to minimize the
  differences between observations and measurements

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WRAP-UP

• The equations of contaminant transport may be
  derived from mass conservation principles
• Diffusion, dispersion and advection have
  discrete meaning
• Simple formulations and optimization/
  calibration procedures may be used to determine
  physical parameters