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Mass Transport of Pollutants

Mass Transport of Pollutants. 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

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Mass Transport of Pollutants

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  1. Mass Transport of Pollutants

  2. 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

  3. 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

  4. 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 Mass flux in Mass flux out z y x

  5. Solutes • Conservative (nonreactive) • Do not react with water or soil, do not biologically or radioactively decay • Nonconservative (reactive)

  6. Physical Processes Controlling Flux • Advection • Solutes carried along by flowing groundwater • Diffusion • Transport by molecular diffusion • Dispersion • Transport by mechanical mixing

  7. Solute Spreading

  8. Advection • Advection • 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

  9. 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)

  10. 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)

  11. 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)

  12. Mass Flux Mass flux in Mass flux out z y x

  13. Mass Balance Equation Mass accumulation

  14. Solution Solution

  15. Error Function

  16. Error Function Values Homework: Problems 881 and 884

  17. Groundwater Monitoring

  18. T08_10_04

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