Transport of NAPLs in
Vadose Zone
National Chiao Tung University
Hsin-yu Shan
NAPL
z
z
z
Liquids that are immiscible with water Æ
nonaqueous phase liquids (NAPL)
NAPLs that have densities that are greater
than water Æ DNAPL (dense NAPL)
NAPLs that have densities that are less
than water Æ LNAPL (light NAPL)
Vadose Zone
Vadose
Zone
Vadose Zone
z
z
Vadose zone contains a three-phase system
of solid, liquid, and gaseous material.
Also called the zone of aeration or
unsaturated zone.
NAPL in Vadose Zone
z
z
z
They may be partially soluble in water, so
that a dissolved phase as well as a
nonaqueous phase may be present
Two-phase flow may occur below the water
table with water and a DNAPL
Three-phase flow may occur in the vadose
zone with air, water, and an NAPL
z
z
z
In the vadose zone the NAPL may partition
into the air as a vapor phase
Flow is dependent upon the densities,
viscosities, and interfacial tensions of the
liquids
In addition to dispersion and diffusion,
compounds can undergo adsorption and
chemical and biological degradation
Release of NAPL
z
z
z
z
Manufacturing/Treatment plants
Dumping
Leaking of storage facilities
Accidental spill
Above-Ground Storage Tanks
z
Petroleum Products
z
z
z
z
Oil refinery
Petrochemical plants
Leaking tanks
Leaking pipelines
Underground Storage Tanks
(USTs)
z
z
z
z
One of the major threat to ground-water
resources
Gasoline stations
Tank farms
Petrochemical plants/Oil refinery
LNAPLs (Light Non-Aqueous
Phase Liquids)
z
z
z
z
Gasoline
Diesel fuel
Jet fuel
BTEX
Organic liquids such as gasoline, which are only slightly soluble in water
and less dense than water, tend to float on the water table when a spill
occurs
DNAPLs (Dense Non-Aqueous
Phase Liquids)
z
Halogenated hydrocarbons - solvents
z
z
z
TCE
PCE
TCA
Organic liquids such as trichloroethylene, which are only slightly soluble in
water and are more dense than water, may sink to the bottom of an aquifer
when a spill occurs
Remediation of LNAPL
Contaminated Aquifer
z
z
Free product recovery
Dissolved species
z
z
Vadose zone
z
z
Pump and treat
Soil vapor extraction
Near ground water table
z
Bioremediation
Remediation of DNAPL
Contaminated Aquifer
z
Ground water
z
z
z
Pump and treat
Steam injection/pump and treat
Vadose zone
z
z
Soil vapor extraction
Excavation/air stripping
Retention and Flow of Liquids
in the Unsaturated Zone
z
z
Vadose zone hydrology is different from
saturated zone hydrology because of the
presence of air in the pore space
The relative proportion of air and liquids in
the pores can vary, and with it can vary the
hydraulic properties of the porous media
Capillary Tension
z
If fluid pressures are measured above the
water table, they will be found to be negative
with respect to local atmospheric pressure
Soil-Water Potential
z
z
z
In unsaturated flow the pore water is under a
negative pressure caused by capillary force
Æ capillary potential, or matric potential, ψ
ψ is a function of the volumetric water content
of the soil, θ
The lower the water content, the lower the
matric potential (the more negative value)
Soil Moisture Potential
φ = ψ(θ) + Z
z
z
Matric potential may be measured as a
capillary pressure, Pc
The total soil moisture potential in terms
of energy per unit volume can thus be
found from:
φEV = Pc + ρ w gz
Soil Water Characteristic
Curves
z
The relationship between matric potential or
pressure head and volumetric water content
for a particular soil is known as a soil-water
characteristic curve, or a soil-water
retention curve
Irreducible minimum
(residual) water content
-1 0 7
-1 0 6
-1 0
P o o r ly so r te d
5
-1 0 4
P ressu re h ead
( c m ) -1 0 3
-1 0
W e ll so r te d
2
bubbling pressure
-1 0
hb
1
-1 0 0
0
0 .1
0 .2
0 .3
W a te r c o n te n t,θ
0 .4
Typical soil-water
retention curves
showing the effect of
grain-size sorting. The
shape of the curves
reflects the distribution
of pore sizes in the soil
z
z
z
The well-sorted soil does not necessarily
have a higher bubbling pressure (The
statement in the textbook is wrong)
Usually it is easier to identify the bubbling
pressure for well-sorted soils, because they
have pores of rather uniform size
For well-sorted soils, the ones that have
smaller grain sizes, will have higher bubbling
pressure
Hysteresis
z
z
z
Determine the SWCC from an initially
saturated soil Æ drying curve
The sample is then resaturated Æ wetting
curve
These two curves will not be the same Æ
hysteresis
Drying scanning curve
ψ
Main drying curve
Main wetting curve
Wetting scanning curve
Volumetric water content,θ
Scanning Curves
The cause of hysteresis
z
z
z
Geometric effect of the shape of single pores
Æ ink bottle effect
The contact angle between water and the
mineral surface is greater when a water front
is advancing (meniscus has a greater radius
of curvature)
Air trapped in the pores during wetting
Ink-bottle Effect
Pore geometry affects equilibrium height of capillary water
during (a) drainage and (b) wetting
Construction of SWCC
z
Lab measurement
z
z
z
z
z
z
Pressure plate assembly – up to 100 bars
Centrifuge
Salt-solution method
Filter-paper method
Thermocouple psychrometer
Field measurement
z
Tensiometer and water content measurement
Air Pressure Pa
Soil
Water
Outlet
Pressure Cell
Pressure
Membrane
(Ceramic plate)
Manifold
Burette
::::::::: ::
::
::::::::::
::::
:::::: ::
::
::
::
::
::::
::::
:::::
:::::::::: ::
::::
::
::::::::::
:::::: ::::
::
::
::
::
::::
:::::
::
Air Pressure
Pressure
Cell
Stand
SWCC Test Setup
Unsaturated Hydraulic
Conductivity
z
z
z
Unsaturated soils have a lower hydraulic
conductivity because some of the pore space
is filled with air and thus cannot transmit
water
Soil moisture in the vadose zone travels
through only the wetted cross section of pore
space
Unsaturated hydraulic conductivity is a
function of water content of the soil K=K(θ)
z
z
As a saturated soil drains, the larger pores
empty first
Because these pores have the greatest porelevel hydraulic conductivity, there is an
immediate large drop in the ability of the soil
to transmit water
-300
-250
-200
Drying
ψ -150
cm water
-100
W etting
-50
0
1
2
3
Hydraulic conductivity (10 -4
4
Relationship between hydraulic conductivity to matric
potential for a wetting and drying cycle illustrating
hysteresis
0
0
10
10
Tested
Tested
K(h)/Ks
K(h)/Ks
-2
10
-2
10
Predicted
Predicted
-4
10
-4
10
-5
-10
1
-10
2
h (cm)
(a) Hygiene sandstone
-10
3
10
0
-10
-10
2
-10
4
h (cm)
(b) Touchet silt loam
Observed values (open circles) and calculated curves (solid
lines) for relative hydraulic conductivity of (a) Hygiene
sandstone and (b) Touchet silt loam G.E.3.
Vapor Phase Transport
z
z
Vapor normally moves by diffusion from
areas where the vapor pressure in the
unsaturated pores is higher to areas where it
is lower
Under special circumstances vapor can move
through the soil under air pressure gradients
as the atmospheric pressure fluctuates
Diffusion of vapor is given by:
∂ρ v
qv = − Dv
∂x
ρv = vapor concentration in the gaseous phase
Dv = diffusion coefficient for water pressure
Preferential Flowpaths in the
Vadose Zone
z
z
There are numerous large pores and crack in
the root zone formed by such agents as plant
roots, shrinkage cracks, and animal burrows
These macropores can form preferential
pathways for the movement of water and
solute, both vertically and horizontally
through the root zone
Related Studies at NCTU
z
z
z
z
z
Retention characteristics of NAPL in sandy
soils
Effect of NAPL on resistivity of soils
Prediction of migration of NAPL using “NAPL
Simulator”
Retention characteristics of NAPL using
micro-models
Relative hydraulic conductivity of NAPL using
micro-models
Retention characteristics of
NAPL in sandy soils
z
z
Jin-fu Huang, Su-hua Cheng, Hsin-yu Shan
(1995-1997)
Use pressure cells to investigate:
z
z
z
SWCCs of immiscible fluid pairs
Applicability of scaling procedure
Results showed that scaling may not give
accurate SWCC
Liquid
σaw or σao
σow
βao
βow
Water
72.7
-
-
-
Gasoline
21.0
51.7
3.462
1.406
Diesel fuel
22.8
49.9
3.189
1.457
Heptane
19.5
53.2
3.728
1.367
TCE
29.3
43.4
2.481
1.675
Use water-air as reference fluid pair
400
400
Soil 1 Ottawa sand(C109)
300
300
200
200
100
100
0
0
Soil 2 Tochen sand - Fines 5%
300
300
200
200
100
100
0
Soil 3 Tochen sand - Fines 10%
300
200
100
0
suction (mbar)
suction (mbar)
0
300
200
100
0
Soil 4 Tochen sand - Fines 20%
300
300
200
200
100
100
0
0
Soil 5 Tochen sand - Fines 30%
300
300
200
200
100
100
0
0
0
10
20
30
40
volumetric water content (%)
(a) air-gasoline system
50
0
10
20
30
40
volumetric water content (%)
(b) water-gasoline system
50
15
50
Gasoline
Suction = 0.3 bar
Volumetric liquid content (%)
Volumetric liquid content (%)
Water
Diesel
Heptane
10
5
Water
Gasoline
Diesel
Heptane
40
30
20
10
0
50
0
Diesel
Heptane
TCE
10
Suction = 0.3 bar
5
Volumetric water content (%)
Volumetric water content (%)
Gasoline
40
30
Gasoline
Diesel
Heptane
TCE
20
10
0
0
0
5
10
15
20
25
30
35
Fines content of Tochen sand (%)
Relationship between residual water
content (0.3 bar) and content of
fines: (a) Liquid-Air; (b) NAPL-Water
0
5
10
15
20
25
30
35
Fines content of Tochen sand (%)
Amount of liquid drained from
saturation to 0.3 bar: (a) Liquid-Air;
(b) NAPL-Water
40
(a) Maximum suction 0.3 bar
(b) Maxiumu suction 1.2 bar
Water
Amount of imbibition
Gasoline
30
Diesel
Heptane
Water(water-gasoline)
20
Water(water-heptane)
10
0
0
5
10
15
20
Fraction fines content
(a)
25
30
0
5
10
15
20
25
30
35
Fraction fines content
(b)
Relationship between amount of trapped liquid (after
complete drainage-wetting cycle) and content of fines
1200
Suction (mbar)
1000
800
600
400
200
0
0
10
20
30
Volumetric liquid content (%)
(a) Air-single liquid system
Scaling of SWCC curves
40
50
Suction (mbar)
600
Ottawa sand
Fines 5% of Tochen sand
Fines 10% of Tochen sand
Fines 20% of Tochen sand
Fines 30% of Tochen sand
400
200
0
0
10
20
30
Volumetric liquid content (%)
Scaling of SWCC curves
Results of NAPL-Water Pairs
40
50
Effect of NAPL on resistivity of
soils
z
z
z
Yun-huei Lai, Fung-chang Kuo, Hsin-yu
Shan (1997-1999)
Measure the resistivity of soil specimens with
NAPL and water in the pores
Variation of resistivity with water content was
basically the same for unsaturated soil with
only water and air in the pores
電極
電極
Power
V
V
Power
Device for measuring resistivity
Va
空氣
空氣
有機液體
Va
Vo
Vw
水
水
Vw
Vs
土壤
土壤
Vs
左圖 Vw　含水比θω
＝ 右圖 Vw+Vo
=
含液比θ
Definition of Water (NAPL) Content
100000
θ= 29.5%
θ=17.8%
θ=45.3%
θ=23.3%
axial restivity, ( KΩ- cm )
axial restivity,ρ (KΩ - cm)
10000
θ=50.7%
θ=55.14%
1000
100
θ=28.9%
10000
θ=33.3%
1000
100
10
10
0
10
20
30
40
Volumetric water content,θω (%)
50
ρ vs. water content - Kaolinite
(water, gasoline) – Axial
direction
60
0
5
10
15
20
25
30
volumetric water conyent,θω (%)
ρ vs. water content – Hsinchu
Clay
(water, gasoline) – Axial
direction
35
10000
θ= 29.5%
θ=17.8%
θ=45.3%
laterial restivity,( KΩ- cm )
laterial restivity,(KΩ- cm)
10000
θ=50.7%
θ=55.14%
1000
100
θ=23.3%
θ=28.9%
θ=33.3%
1000
100
10
10
0
10
20
30
40
volumetric water content,θω (%)
50
ρ vs. water content - Kaolinite
(water, gasoline) – Lateral
direction
60
0
5
10
15
20
25
volumetric water conyent,θω (%)
30
35
ρ vs. water content – Hsinchu
Clay (water, gasoline) – Lateral
direction
Prediction of migration of
NAPL using “NAPL Simulator”
z
z
z
z
Kuo-lung Ou, Liang-chen Chang, Hsin-yu
Shan (1999-2000)
NAPL Simulator takes k-S-P relationship of
all fluid pairs into account
Actual and scaled S-P data obtained in
previous studies are used
Results of simulation indicated that using
water-air SWCC gave more reasonable
predictions
-4.5
-4.50
-14.5
-4.5
-14.50
-24.5
-14.5
-4.5
-4.5
-4.5
-14.5
-14.5
-14.5
-24.5
-24.5
-24.5
-34.5
-34.5
-34.5
-24.50
-24.5
-34.5
-34.50
-34.5
-44.5
-44.50
-44.5
-44.5
-44.5
-44.5
-54.5
-54.50
-54.5
-54.5
-54.5
-54.5
-64.5
-64.50
-64.5
-64.5
-64.5
-64.5
-74.5
-74.50
-74.5
-74.5
-74.5
-74.5
-84.5
-84.50
-84.5
-84.5
-84.5
-84.5
-94.5
-94.50
-94.5
-94.5
-94.5
-94.5
-104.5
-104.50
-104.5
-104.5
-104.5
-104.5
-114.5
-114.50
0
7 15 22 29 37 44 51 58 66 73
-114.5
0
7 15 22 29 37 44 51 58 66 73
-114.5
0
7 15 22 29 37 44 51 58 66 73
Distribution of degree of saturation of
gasoline (t=66000 sec), fluid pair: (a)
GN, (b) GW, (c) NW– disregard
hysteresis effect
-114.5
0
7 15 22 29 37 44 51 58 66 73
-114.5
0
7 15 22 29 37 44 51 58 66 73
0
7
15 22 29 37 44 51 58 66 73
Distribution of degree of saturation of
gasoline (t=66000 sec), fluid pair: (a)
GN, (b) GW, (c) NW– consider
hysteresis effect
-4.5
-4.50
-4.5
-4.5
-4.5
-4.5
-14.5
-14.50
-14.5
-14.5
-14.5
-14.5
-24.5
-24.50
-24.5
-24.5
-24.5
-24.5
-34.5
-34.50
-34.5
-34.5
-34.5
-34.5
-44.5
-44.50
-44.5
-44.5
-44.5
-44.5
-54.5
-54.50
-54.5
-54.5
-54.5
-54.5
-64.5
-64.50
-64.5
-64.5
-64.5
-64.5
-74.5
-74.50
-74.5
-74.5
-74.5
-74.5
-84.5
-84.50
-84.5
-84.5
-84.5
-84.5
-94.5
-94.50
-94.5
-94.5
-94.5
-94.5
-104.5
-104.50
-104.5
-104.5
-104.5
-104.5
-114.5
-114.50
0
7 15 22 29 37 44 51 58 66 73
-114.5
-114.5
0
7 15 22 29 37 44 51 58 66 73
0
7 15 22 29 37 44 51 58 66 73
Distribution of degree of saturation
of water (t=66000 sec), fluid pair: (a)
GN, (b) GW, (c) NW – disregard
hysteresis effect
-114.5
0
7 15 22 29 37 44 51 58 66 73
-114.5
0
7 15 22 29 37 44 51 58 66 73
0
7 15 22 29 37 44 51 58 66 73
Distribution of degree of saturation
of water (t=66000 sec), fluid pair: (a)
GN, (b) GW, (c) NW – consider
hysteresis effect
-7
-7
-7
-7
-7
-7
-17
-17
-17
-17
-17
-17
-27
-27
-27
-27
-27
-27
-37
-37
-37
-37
-37
-37
-47
-47
-47
-47
-47
-47
-57
-57
-57
-57
-57
-57
-67
-67
0
3
7 10 13 16 20 23 26
-67
-67
0
3
7 10 13 16 20 23 26
0
3
7 10 13 16 20 23 26
Distribution of degree of saturation of
TCE (t=8693 sec), fluid pair: (a) GN,
(b) GW, (c) NW– disregard
hysteresis effect
-67
0
3
7 10 13 16 20 23 26
-67
0
3
7 10 13 16 20 23 26
0
3
7 10 13 16 20 23 26
Distribution of degree of saturation of
TCE (t=8693 sec), fluid pair: (a) GN,
(b) GW, (c) NW– consider hysteresis
effect
-7
-7
-7
-7
-7
-7
-17
-17
-17
-17
-17
-17
-27
-27
-27
-27
-27
-27
-37
-37
-37
-37
-37
-37
-47
-47
-47
-47
-47
-47
-57
-57
-57
-57
-57
-57
-67
0
3
7 10 13 16 20 23 26
-67
-67
0
3
7 10 13 16 20 23 26
0
3
7
10 13 16 20 23 26
Distribution of degree of saturation of
water (t=8693 sec), fluid pair: (a) GN,
(b) GW, (c) NW– disregard
hysteresis effect
-67
-67
0
3
7 10 13 16 20 23 26
-67
0
3
7 10 13 16 20 23 26
0
3
7 10 13 16 20 23 26
Distribution of degree of saturation of
water (t=8693 sec), fluid pair: (a) GN,
(b) GW, (c) NW– consider hysteresis
effect
Retention characteristics of
NAPL using micro-models
z
z
z
Yung-chi Shi, Hung-huei Chen, Liang-chen
Chang, Hsin-yu Shan (2000-2001)
Micro-models are made of acrylic
Analyze the images recorded by CCD by
CCD to study the distribution of fluids in the
pores and throats
2.
孔 隙 （Po r e）
2m
Micromodel
m
通道（Throat）
Pores and throats of the micromodel
不鏽鋼接頭
六角螺絲
壓克力厚塊
微模型塊
壓克力薄板
壓克力厚塊
六角螺帽
CCD攝影機
架設於XY TABL E上
Assembled micromodel
TYGON軟管
微模型
Experimental setup
照明燈座
液體儲存槽
9
8
7
毛細壓力（CM）
6
5
空氣對水渲排曲線
4
空氣對水汲取曲線
3
2
Water-air SWCC
1
0
0
0.2
0.4
0.6
0.8
1
1.2
飽和度
9
8
毛細壓力（CM）
7
6
5
空氣對水排退曲線
4
理論估算值
3
2
1
0
0
0.2
0.4
0.6
飽和度
0.8
1
1.2
Water-air SWCC –
experimental results vs.
theoretical curve
4
3.5
毛細壓力（CM）
3
2.5
空氣對柴油渲排曲線
2
空氣對柴油汲取曲線
1.5
1
Diesel fuel-air SWCC
0.5
0
0
0.2
0.4
0.6
0.8
1
1.2
飽和度
4
3.5
毛細壓力（CM）
3
2.5
空氣對柴油渲排曲線
2
理論估算值
1.5
1
0.5
0
0
0.2
0.4
0.6
飽和度
0.8
1
1.2
Diesel fuel-air SWCC –
experimental results vs.
theoretical curve
12
空氣對水渲排曲線
11
10
9
柴油對水渲排曲線
毛細壓力（CM）
8
7
6
5
以空氣對水為參考流體對，
比例縮放所得之曲線
4
3
2
1
以柴油對空氣為參考流體對
，比例縮放所得之曲線
0
0
0.2
0.4
0.6
0.8
1
1.2
飽和度
Comparison of scaled SWCC
Relative hydraulic conductivity
of NAPL using micro-models
z
Yuan-junn Lu, Liang-chen Chang(20012002)
Conclusions
z
z
z
Transport/Distribution of NAPL in vadose zone is a
complex problem
Issues to be investigated: effect of variation of
contact angle, relative permeability, scaling effect,
three phase behavior
Important properties that may have significant effect:
z
z
Properties of NAPL such as: density, viscosity, surface
tension, interfacial tension
Soil properties such as: pore size distribution, saturation
history, wettability
Comments and
Questions?
-10
6
θ r =0.10
-104
Pressure head
(cm)
-10
P
2
hb
θs =0.50
-100
0
0.1
0.2
0.3
0.4
0.5
0.6
Water content, θ
Typical soil-water retention curve