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7/31/2019 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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