bab 3 contaminant migration pathway.pptx

7/27/2019 bab 3 contaminant migration pathway.pptx

1/19


2/19

NUR HANANI BT ABD HALIM 04DKA11F1038

SITI AISYAH SUFIYYAH BT MOHAMAD

ANUAR

04DKA11F1993

NUR AINA ALIA BT ANNUAR GOH

04DKA11F1078


3/19


4/19

Contaminant can enter soil through: Dissolve in liquid phase in soil

Absorb inorganic matter in soil

From mineral structure residue


5/19

Water solubility Maximum amount of a contaminant that can be

dissolved in the water at a specified temperature.

Polarity of the compound Plays a major role in mobility of the compound.

Polar substances and therefore absorb to soilparticles less.

Kow (Octanol water partition coefficient) A measure of the hydrophobicity of an organic

compound.


6/19

Chemical fate is the eventual short-term orlong-term disposition of chemicals, usuallyto another chemical or storage.

Examples of short-terms and long-term fatesChemical Media Short-term fate Long-term fate

PCB Soil and water Absorbed to soil BiomediateddegradationPCB Atmosphere Absorbed to aerosols PhotocatalyzeddegradationCO Water Reactions to carbonate andbicarbonate Photosynthesis tooxygen and biomass

Benzene Water Absorbed to suspendedparticles BoiremediateddegradationAmmonia Soil and water Reaction to ammonium Boiremediateddegradation

PCB, polychlorinated biphenyl.


7/19

Soil, the fragile and fertile interface betweenthe atmosphere and the subterranean realm,is characterized by massive transfer of massand energy.

Energy and mas fluxes through this porousmedium of the soil are not significant for thehealthy functioning of soil as the clean and

productive base for agriculture, but also theyare critical for the role that the soil plays inprotecting the environment of bothunderground surface reserves of water.


8/19

A transport process, as used herein, is onethat moves chemicals and other properties ofthe fluid through the environment.

Diffusion of chemicals Molecular Diffusion Convection or advection Turbulent diffusion

Dispersion Interfacial transfer Multiphase transport


9/19

Mixing is a rate-related parameter, in that mostrates of reaction or transport are dependent onmixing in environmental system.

When mixing is dominant, the first order rateequation can be described as:

Rate of process= mixing parameter x different of equilibrium


10/19

A important concept for environmenttransport is resistances. The inverse of a rateparameter is a resistance to chemicaltransport.

Or in equation form :1/rate parameter = resistance to chemical transport


11/19

As specific chemical element and compound

may exist in groundwater in any of thefollowing forms: Free ion surrounded by water molecules Insoluble species Metal ligand complexes Absorbed species Specie held on ion exchange Species that differ by oxidation state.

The mass transfer can be divided into two

groups: Abiotic refers to those that are non biological in

nature. Biotic involves mass consumption of the

chemicals by microorganism.


12/19

Advection - dissolved substances carriedalong with bulk fluid flow.

Hydrodynamic Dispersion Solute spreadsout from path expected to be followed byadvection alone.

Pore channel velocity: molecules travel at differentvelocities.

Mixing of pore channels, tortuosity, branching.

Differences in pore sizes ( different velocities ) Variables conductivity in soil layers.

Molecular diffusion


13/19

Abiotic process : to those that are nonbiological

in nature. The microorganisms involved in the biotic

process: Acid base reaction

Hydrolysis of organic chemical Oxidations Complexation Precipitation & dissolution Exsolution & votilization

Radioactive decay Sorption

Biotic processes : involve mass consumption ofthe chemicals by microorganisms, often referred

as biodegradation.


14/19

The principles discussed in the previous sectionwill enable us to formulate conceptually howNAPLs move into the subsurface.

Because of some important effects of density ofNAPLs on the transport phenomena, it isconvenient to treat the LNAPLs and DNAPLsseparately

Compound which display extremely low aqueoussolubility can exist as a separate liquid phase ingroundwater systems, if present in sufficientquantities.


15/19

In groundwater system, these contaminantsphase are referred to as nonaqueous phaseliquids (NAPLs) and their behavior will be

fundamentally different from that of the bulkaqueous phase.


16/19


17/19

Ficks law of diffusion:J =-D*C/X

J=The mass flux , D=Effective effusion , C/X=concentration gradient

Advection This equation applicable when

The soil is saturated

Flow is steady

Darcys Law is applicable

Q =-KA dh/dl

Q= rate of water flow, K=hydraulic conductivity,

A= column cross sectional area, dh/dl=hydraulic gradient Radioactive decay & degradation


18/19

Transport time of groundwater between twowells.

Calculation of groundwater velocity:unfractured clayey aquitard.

Calculation of groundwater velocty and traveltime across an unfractured clay aquitard.

DNAPL movement in a groundwater.


19/19

bab 3 contaminant migration pathway.pptx

Documents

Transcript of bab 3 contaminant migration pathway.pptx