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**Mass Transport of Pollutants**

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**Dense Non-Aqueous Phase Liquids**

NAPLs – Insoluble in water and Separate phase Dense NAPLs – More dense than water Chlorinated hydrocarbons Trichloroethylene-TCE Tetrachloroethylene-PCE Density increases with increasing halogenation Density difference of 0.1% causes sinking

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**Light Non-Aqueous Phase Liquids**

Light NAPLs Lighter than water Petroleum hydrocarbons Oil Gasoline Density difference between water and NAPL of 1% can influence flow Low viscosity NAPLs migrate more rapidly than high viscosity NAPLs

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Transport Processes Conservation of Mass for dissolved substances in groundwater Rate of change of mass = Flux of mass out – Flux of mass in ± gain or loss of mass due to reactions x y z Mass flux in Mass flux out

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**Solutes Conservative (nonreactive) Nonconservative (reactive)**

Do not react with water or soil, do not biologically or radioactively decay Nonconservative (reactive)

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**Physical Processes Controlling Flux**

Advection Solutes carried along by flowing groundwater Diffusion Transport by molecular diffusion Dispersion Transport by mechanical mixing

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Solute Spreading

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**Advection Advection f = porosity vx = average velocity**

Solutes carried along by flowing groundwater f = porosity vx = average velocity F = Advective flux = Total mass of solute which is carried across a unit area oriented normal to the bulk fluid motion

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**Diffusion Diffusion Molecular-based phenomenon**

Net movement toward areas of lower concentration F = mass flux per unit area per unit time (M/L2/T) D* = apparent diffusion coefficient in soil (L2/T) C = solute concentration (M/L3) ∂C/∂x = concentration gradient (M/L3/L)

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**Dispersion Mechanical Dispersion**

Transport by mechanical mixing F = mass flux per unit area per unit time (M/L2/T) Dx = dispersion coefficient (L2/T) C = solute concentration (M/L3) ∂C/∂x = concentration gradient (M/L3/L)

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**Advection-Dispersion Equation**

F = mass flux per unit area per unit time (M/L2/T) Dx = dispersion coefficient (L2/T) C = solute concentration (M/L3) ∂C/∂x = concentration gradient (M/L3/L)

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Mass Flux x y z Mass flux in Mass flux out

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Mass Balance Equation Mass accumulation

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Solution Solution

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Error Function

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Error Function Values Homework: Problems 881 and 884

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**Groundwater Monitoring**

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T08_10_04

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