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Fundamentals of Contaminant Hydrogeology

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    Environmental Biotechnology Lab

    Jihoon Yang

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    Degree of Localiztion

    - Point source

    : Identifiable, Small-scale source

    Make a reasonably well-defined plume

    - Non Point source

    : Larger-scale source,Mixing of poorly defined many smaller source

    Loading History

    - Pulse Loading

    : Fixed concentration

    Short time

    - Continuous source Loading

    : Constant concentration

    Over long time Fig 16.1

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    Kinds of Contaminants emanating

    - Volatiles

    - Base-neutral

    - Extractable

    - Acid extractable

    - Pesticides

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    Radionuclides

    : Nuclear industry, During mining of raw materialNeutron activation

    ex) U238 U239 + e-

    : Cancer, Genetic defects

    Trace elements(metals)

    : Effluents from mining, industrial waste water

    Runoff/solid waste/waste water of urban area

    Agricultural waste/fertilizer, fossil fuels

    : Accumulate in the body

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    Nutrients

    : Nitrogen, Phosphorus (Especial ly Nitrate): Fertilizer, cattle feeding operation, cultivation, sewage

    : Causing methemoglobinemia/cancer

    Other inorganic species: Ca2+, Mg2+, Na+, Ci-, F-

    : Problem with Salinity

    Organic contaminants

    : Soluble aromatic hydrocarbons (ex. BTEX)

    (From petroleum fuel, lubricant)

    : Very harmful for human

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    Biological contaminants

    : Human/animal sewage or wastewater: Pathogenic bacteria, viruses, parasites

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    Starting of Spread

    : Large extent to Small extentHigh Concentration to Low Concentration

    Magnitude and Direction of Advective Transport

    : Hydraulic conductivity distribution

    Configuration of the water table

    Presence of sources or sink

    Shape of the flow domain

    This parameters affect groundwater velocity

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    Steady State

    No dispersion or Reaction

    Only Hydraulic Conductivity

    affect shape of spread

    Plume spreading to Low

    hydraulic conductivity layer

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    Steady State

    Adding dispersion

    Plume size increases

    The maximum concentrationdecrease

    Where L : Longitudinal

    dispersivity

    T : Transverse

    dispersivity

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    Steady State

    Adding Radioactive decay

    (1st order decay)

    Smallest plume is made by

    Smallest half time

    Where t1/2 : half life constant

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    Steady State

    Adding Ion exchange

    Ion exchange is related with

    Sorption

    Where Ks :Changing selectivity

    Coefficient

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    Non constant loading

    Inflow concentration is

    different, but inflow time

    is same

    The final concentration isequal but the plume size is

    different

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    Fractured and Karst system

    Plumes form is made by

    The pattern of flow

    Ground water flow is typically

    convergent toward majorconduits

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    Saturation

    : Relative abundance of fluid in a porous media as the volumeof the ith fluid per unit void volume for fluid

    : where Vi : volume of the ith fluid

    Vvoids : volume of the void

    : Sum of all the components saturation is equal to 1

    Wettability

    : Tendency for one fluid to be attracted

    to a surface in preference to another

    : Only direct measure of wetting is

    The Contact Angle

    : Tangent < 90 : Test liquid is Wetting

    Tangent > 90 : Test liquid is Non-Wetting

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    Imbibition

    : Displacement of the nonwetting fluid by the wetting fluid

    Drainage

    : Displacement of the wetting fluid by the nonwetting fluid

    Water being added to a dry soil

    Water : imbibition

    Nonwetting organic liquid : drainage

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    Relative Permeability

    : Explain the tendency for fluid to interfere withone another as they flow

    Darcys eq written in terms of pressure gradient

    where qi : flow of the ith fluid per unit area of the medium

    ki : effective permeability of the medium to ith fluid

    : viscosity, P : pressure

    In here, relative permeability of ith fluid is

    Where ki : effective permeability of the medium to ith fluid

    k : the intrinsic permeability

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    : Finally, general form of Darcys eq for multifluid flow is

    kkri range between zero and one

    If two or more liquid are present in the system, kkri value is decrease

    : The relative permeability curve

    1) both fluids are present, the relative

    permeabilities rerely sum to one

    2) Some quantity of either wetting

    or nonwetting fluid in the pore

    system cannot move below some

    saturation threshold

    3) krn > krw : Because wetting fluid

    occupies the smaller pores, the flow

    is slow

    Where Sw : Saturation of wetting fluid

    This Point is the Residual Saturation

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    Residual Saturation

    : Of wetting fluid Pendular saturationheld by Capillary force in the narrowest part of the pore size

    Of nonwetting fluid Insular saturation

    isolated blob in the center of the pore

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    Downward migration of liquid

    occurred by potential gradient

    Because NAPL is wetting phase,

    when the NAPL spill into wetted

    soil, the NAPL moves from pore

    to pore once saturation exceeds

    the residual saturation

    Main threat to a ground water

    is opportunity for continuingdissolution or volatilization as the

    spill remains

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    When NAPL reach at layer ofunsaturated zone, NAPL has a

    tendency to spread horizontally

    as it moves downward

    If that layer uncontinuous theNAPL will eventually spill over

    and continue to move downward

    toward the water table

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    Large volume of contaminants

    over a relatively short time causes

    rapid downward and lateralmigration

    Slow leakage over a long time,

    the contaminant moves along the

    most permeable pathways

    More mobile liquid will reach the

    water table from slow leakage

    When the NAPL reachs thecapillary fringe, because water

    saturates a large proportion of

    pores, free product accumulates

    near the top of the capillary fringe

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    Large volume of fluid reachingover a relatively short time,

    collapses the fringe and

    depresses the water table

    Slow rate of supply has little

    affect on the capillary fringe or

    the configuration of water table

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    Case of DNAPL, the quantity

    of concentration within poreexceeds the residual saturation,

    downward percolation continues

    Driving force of DNAPL is

    difference of density between

    the DNAPL and ground water

    Direction of flow is different

    than the ground water

    Heterogeneity within the

    saturated zone cause to spread

    laterally

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    Considerations in design

    1) Close interval point sampling2) Sample location

    Determine the character and complexity of flow

    Using the piezometer sampling,

    hydraulic head is the same in either

    case, but concentration of

    contaminant is different according

    to sampling point

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    Contamination of samples with fluids because of drilling

    : Reuse the drill(Using where contaminated difference material): The solution is development well

    Changing in water quality caused by the presence of the well

    : Well made by cement

    : Cement contaminated water has high pH(above 9)

    Sample deterioration

    : By changing temperature, pressure, gas content ,

    sample will change(ex. Addition of oxygen, Loss of CO2)

    : Solution is using the specialized sampling equipment and

    use of flow cell at the well head

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    Sloppy field and laboratory practices

    : Sample contamination caused by improper bottle washing,filtering, or the use of impure preservatives

    : Solution is prudent to check before sampling

    Submitting the known concentration, duplicate samples, replicate

    samples

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    Nests of conventional standpipe piezometer

    1) Property :

    Provide vertically spaced water sample

    2) Advantage :

    - Less difficulty in installing seals

    - Easy to measuring water levels

    - Extremely durable with little

    possibility of failure

    3) Disadvantage :

    - Higher cost of drilling additionalboreholes

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    Various multilevel devices installed in a single borehole

    1) Property :

    Involves placing several samplers at

    various depths in a single borehole

    2) Advantage :

    - Large number of discrete samping

    points

    - Relatively low cost

    - Most economical for near surface

    investigation

    3) Disadvantage :

    - difficult to develop the screen

    - Hard to design a water level

    mesurement equipment

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    Packer arrangement that can be moved to various positions in an

    uncased borehole in rock or cohesive sediments1) Property :

    Sample continuously in an uncased

    borehole

    2) Advantage :

    - Cost is low

    3) Disadvantage :

    - Possibility for fluid communication

    within the borehole

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    Characterizing the distribution of LNAPLs

    Specially designed soundermeasures the thickness of

    LNAPL floating on the water

    column in a water table

    observation well

    Provides the apparent

    thickness of spilled product,

    which is often larger than the

    true product thickness

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    Pulling the fluid under vacuum through a porous ceramic cup into a

    containerSample is removed by suction or by gas displacement

    Useful for sampling when the state of saturation change freequently

    Fluid composition to change from reaction with the ceramic cup or

    from the loss of gases as the sample is collected under vacuum

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    Drilling and coring

    Fluids squeezed out of the sample can be analyzed in the normalmanner

    Determine contaminant concentrations in the dried solid and report

    contaminant concentration as mass of contaminant per unit mass of

    solid

    Advantage

    1) Spatial control in being able to relate specific concentration of

    contaminant to specific lithologies

    2) Ability to minimize contamination due to the sampling method

    Disadvantage

    Expansive of rig back, too much drilling occur contamination

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    Rapid & Inexpensive method

    Successful when contamination is manifested in a secondary way

    Soil-gas characterization

    Hollow metal probe, Activated charcoal

    Advantage : sampling at a much larger number, economical

    Caution : 1) Low permeability layer

    2) How the contaminant occurs

    3) Contaminants are present in localized fracture zone

    Geophysical Methods

    Mesuring resistivity, Electromagnetic conductivity method

    If data had a different property compare with another zone, That

    zone is a contaminated zone

    Consideration : natural variability in geology or water chemistry

    insufficient contrast in electrical conductivity or

    resistivity between plume and ground water

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