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297
MIGRATION OF SOME POLLUTANTS THROUGH CLAYEY AND SANDY
SOILS: CENTRIFUGE MODELLING
M. S. S. Almeida
Departamento de Engenharia Civil - COPPE
S. B. Gurung
Depart. of Civil Engineering & Environmmental Engineering Hiroshima University Japan
ABSTRACT: This paper presents the migration of benzyl amine and salicylic acid through
bentonite soil layer and migration of zinc through dredged sediments carried out in the Mini-Drum
centrifuges of Hiroshima University Federal University of Rio de Janeiro. Two types of dredged
sediments; one with only sand content and the other with 5% of silt and 28% of clay content were
used for the purpose of studying the migration behavior of heavy metals through these soils. The
Mini-Drum centrifuge was chosen for carrying out these studies because of its potential to
accelerate the flow N (scale factor) times faster than in the corresponding prototype and at the same
time maintaining approximate field stress condition in the models. Therefore, both type of models
i.e. bentonite models and dredged sediment models were carried out in accelerated gravity field of
105-g and 50-g respectively for making it possible to migrate the chosen pollutants through clayey
and fine grain soils. From the test results, bentonite shows the good potential of attenuating benzyl
amine and salicylic acid and therefore may be a good material in sealing or containing organic
chemicals wastes. Whereas, heavy metal like zinc is attenuated well by dredged sediments when
the dredged sediments contain finer grain fractions in the sediments.
1.INTRODUCTION
Domestic, industrial or chemical wastes
generated put a challenge to Civil Engineers
for making the proper disposable site or
remediating the contaminated sites in years to
come. At present, in civil engineering practice,
low permeability clay soils are used as a liner
material or cut-off wall material, for containing
or sealing-off the underground flow of various
fluids, such as leachates from a sanitary
landfill, oils from a storage reservoir,
chemicals from a chemically contaminated
site. In order to assess the potential of the
centrifuge modeling of geoenvironmental
problems, two different studies have been
carried out and these are outlined in the next
section.
2.CENTRIFUGE MODELING STUDIES
The first study was related with the
capability of low permeability clay soils in
containing some organic compounds. For this
purpose, benzyl amine and salicylic acid,
which are organic base and acid respectively
were chosen as representative of organic
chemicals to study the attenuation potential of
bentonite against these chemicals. Test results
were fitted to 1-D advection dispersion
equation to obtain the migration parameters.
The second study was related with problems
that may be faced by the civil engineers when
dredging lagoon sediments. Some of these
sediments may have some degree of
contamination with heavy metals such as zinc,
cooper, chromium and cadmium (Almeida, et
al. 1998, 1999; Borma et al, 1998). In the next
3. THEORY
Assuming that advection, dispersion and
sorption are the only transport processes
involved, the equation used to describe the
movement of a solute in saturated,
homogeneous porous media during one-
dimensional steady flow is (Bear, 1979; Freeze
and Cherry, 1979):
t
Q
x
C
u
x
C
D
t
C
oo ¶
¶
-
¶
¶
-
¶
¶
=
¶
¶
2
2
 (1)
where, C is the concentration of the solute in
the aqueous phase; Q is the sorbed mass of the
solute per unit mass of solid phase; is the
porosity; is the bulk density; D is the
longitudinal dispersion coefficient, v is the
mean pore-water velocity in the x direction; x
is the distance and t is time. The solution of
equation (1) requires a relationship between Q
and the aqueous phase concentration C, which
is most commonly given by
CKQ d= (2)
the constant Kd is being referred to as the
distribution or partition coefficient. Combining
equation (2) with (1) leads to:
x
C
u
x
C
D
t
C
R ood -= 2
2
 (3)
where Rd, the retardation factor, is
R
K
d
d= +1 (4)
Equation 3 implies that the porosity q and
the volumetric flux remain constant in time
and space (steady-state flow) and it is applied
for modelling one-dimensional transient
transport with linear, reversible, instantaneous
sorption. Following the analytical approach as
suggested by Yamaguchi et al. (1989), the
solution of Eq. (3) is given by :
[ ] [ ] [ ]
Dt
utx
D
ux
Dt
utx erfcerfctxC
42
1
42
1* exp),( +- += (5)
where, C*(x,t) is relative concentration at any
depth x, at time t, u is average interstitial
velocity = uo/Rd, D is advection-dispersion
coefficient = Do/Rd. Using first-term
approximation method, Equation (5) reduces
to:
1
2 4
 (6)
where, Ci
* is relative concentration, L is depth
of soil, i = 1,2, ..... ,n. and
1 2
1 1 2 2
1 2 2 1
;
2
4 1 2
2 1
1 2 2 1
2
 (7)
 is argument of complementary error
function.
No literature regarding the modelling of
adsorption process using the geotechnical
centrifuge was available, rather to avoid this
problem researchers seem to have used
conservative tracers. Therefore, for the sake of
working assumption, amount of chemicals as
well as zinc adsorbed on the soil surface have
been calculated by using the equation of mass
conservation which can be written as:
S mc V C
M
== -- ´´ (8)
where, S is the content of chemicals adsorbed
(g/kg), mc is total mass of chemical in the
solution (g), V is volume of liquid in the
system (L), and C is concentration of the liquid
draining out from the centrifuge (g/L). The
total stress (s ) acting on the soil model in the
increasing direction of the centrifuge radius is
given by the relation:
(( ))== ++òò . /2
0
2
z
tR z (9)
where, w is rad/sec of centrifuge, Rt, is radius
to the top of the model and z, the depth in the
soil model.
3.1 - 3. Reduction of Centrifuge Test Data
The principle of physical modelling of
pollution migration, through the soil mass
using geotechnical centrifuge, is governed by
the fact that if identical fluids in model and
prototype are used, and the average Darcy’s
velocity is maintained. Then the permeability
of the soil model can be calculated from the
rate of discharge (Qm), flowing across the
cross-sectional area (Am) under the hydraulic
gradient (im). The prototype permeability
coefficient (kp) is related to model permeability
coefficient (km) by the relation
mm
mm
AiN
Q
N
k
pk ´´== (10)
Furthermore, scaling laws for the transport
of solute through a layer of soil are as follows:
(Hensley, 1989)
t N tp m=
2 (11)
V
V
Np
m= (12)
mp DD = ifPe <1 (13)
N
D
D mp = if Pe >1 (14)
where, t is time; V is interstitial velocity; D is
hydrodynamic dispersion; N is the scale factor;
Pe is the Peclect number and the indices p and
m refer to prototype and model values
respectively. The dependence of hydrodynamic
dispersion on the Peclect number is discussed
for example, by Bear (1979). The dispersion is
velocity dependent for higher Peclect number
(Pe>1).
4. MINI-DRUM CENTRIFUGE
Model tests were carried out in geotechnical
centrifuge. Migration of organic chemicals
through the bentonite sand layer was
performed in the Mini-Drum centrifuge of
Hiroshima University whereas migration of
zinc through dredged materials were conducted
in the Mini-Drum centrifuge of Federal
University of Rio de Janeiro. Brief descriptions
on both centrifuges have been given below. A
typical diagram of a mini-drum centrifuge isshown in Figure 1.
Figure 1 Schematic diagram of Mini-drum
centrifuge
4.1. Mini-Drum Centrifuge of Hiroshima
University
Mini-Drum centrifuge of Hiroshima
University has 80-cm. diameter. It houses a
ring channel that holds the soil model. The ring
channel has the internal dimension of 18.5 cm.
as width, 11.5 cm. as depth and an outermost
radius of 37.2 cm. The drum can be rotated
from axis horizontal mode to axis vertical
mode while it is running at or below 260 rpm
and facilitate the pouring of bentonite-sand
slurry. At axis vertical mode, the drum can be
rotated up to 1000 rpm. At a linear modelling
scale of N=105, the inside dimensions of the
ring channel can model a prototype soil of
length = 210 m. width = 18.9 m. and depth =
11.5 m.. Data from the models are routed
through slip rings to the externally installed
data acquisition system.
300
4.2. Mini-Drum centrifuge of Federal
University of Rio de Janeiro
This centrifuge has a ring channel of
internal diameter = 1.0 m, a height = 0.25 m
and a depth = 0.17 m. The face plate, where
the instrumentation is housed, is 0.7 m. in
diameter. The centrifuge is provided with a tilt
mechanism similar to Hiroshima University to
facilitate model preparation. With the main
drive axis in the vertical direction, the
centrifuge can be run at 900 rpm (450-g),
carrying a payload of 200 kg. The on board
data acquisition system consists of a flight PC
with 16 channel unity for signal conditioning
of the instrumentation, with the capacity to up
grade to 32 channels, if necessary. It is
possible to control the fluid levels in the ring
channel via digitally controlled standpipe
motors with position feedback. In-flight
instrumentation includes pore pressure
transducers, resistivity probes, temperature
probes and displacement transducers.
5. MATERIAL USED
5.1 Bentonite
The bentonite used in this research was
purchased from Katayama Chemicals, Osaka,
which has the pH value around 10 and is a Ca-
montmorillonite. Griffin et al. (1976) suggest
that the Ca-montmorillonite does not produce
shrinkage cracks (synersis) as it’s counterpart
Na-montmorillonite and therefore, it is
believed that the uniform bed of bentonite
layer is formed in the soil model. Enagi sand
was used for making the incompressible bed
under the bentonite layer in order to smooth
the flow of chemicals. The Enagi sand has d10
and d60 as 0.14 mm. and 0.4 mm. giving
coefficient of uniformity (Cu) and coefficient
of curvature (Cc) as 2.86, and 1.12,
respectively. The average grain size (d50) was
0.35 mm. and according to JSF classification
(JSSMFE, 1990) this sand was classified as
poorly graded sand (SP). Therefore, it should
provide pervious and incompressible base for
the overlain bentonite layer at 105-g in Mini-
Drum centrifuge. The circular hole through the
soil model is the space of a soil sample taken
for the vane shear test. Test result on vane
shear test have been described elsewhere
(Gurung et al., 1996).
5.2 Chemicals
The chemicals benzyl amine and salicylic
were selected on the ground of safety in
handling. Properties of these chemicals are
presented in Table 1. To maintain the
compatibility of testing equipment with the
chemicals used and for the sake of easy
detection of the chemicals during the chemical
analysis, initial concentration of the benzyl
amine and salicylic acid were prepared as 4.88
g/L and 0.96 g/L respectively. From the initial
concentration of the solution it is obvious that
the amount of chemical compared to volume of
water is negligible, therefore during the
calculation, density of the chemical solution is
taken as density of water. The soil models
where solution of benzyl amine and salicylic
acid was permeated have been named as
BNmin and SALIcid, respectively in this
paper.
Table 1. Properties of organic chemicals
Chemicals Benzyl
amine
Salicylic acid
Molecular wt. 107.16 138.13
Physical state Liquid Acicular
crystal
pH 11 2.54
Solubility in
water
Infinity 2.2 g/L
5.3 Dredged materials
Grain size distributions of the dredged
material i.e. Sao Francisco sand and Bento
Rivbeiro sand are shown in Figure 2. Note that
Bento Rebeiro sand has more clay content than
Sao Francisco sand. According to the Unified
Soil Classification System São Francisco soil
(SF) can be classified as a poorly graded sand
(SP) and the Bento Ribeiro soil (BR) as a
clayey sand (SC). Index properties of these
soils are given in Table 2.
5.4 Zinc
In the present study, zinc was selected as
the heavy metal pollutant for migrating
301
through the soil model of dredged sedimentary
deposits. Zinc solutions were prepared from
Zinc nitrate [Zn(NO3)26H20] powder at an
initial concentration of about 200-ppm. Zinc
solution fractions that had migrated through
the soil models were collected regularly and
sent for titration immediately. The reagent
used for detecting the concentration of zinc
was ethylenediaminetetra acetic acid disodium
salt [C10H14N2O8Na2.2H2O] prepared at a
concentration of 0.001M.
Table 2. Properties of Sao Francisco and Bento
Ribeiro sand Models
Properties Sao
Francisco
Bento
Ribeiro
Sand (%) 100 67
Silt (%) - 5
Clay (%) - 28
wL (%) - 41
wP (%) - 17
Organic matter (%)0.148 1.53
CEC (cmole/kg) 1.6 4.5
pH value 6.6 6.2
Specific Gravity,
Gs
2.59 2.67
maxdg (gf/cm
3) 1.57 1.88
w opt (%) 4.6 13.4
Pore volume (cm3) 1257 948
5.4 Zinc
In the present study, zinc was selected as
the heavy metal pollutant for migrating
through the soil model of dredged sedimentary
deposits. Zinc solutions were prepared from
Zinc nitrate [Zn(NO3)26H20] powder at an
initial concentration of about 200-ppm. Zinc
solution fractions that had migrated through
the soil models were collected regularly and
sent for titration immediately. The reagent
used for detecting the concentration of zinc
was ethylenediaminetetra acetic acid disodium
salt [C10H14N2O8Na2.2H2O] prepared at a
concentration of 0.001M.
6. TESTING PROCEDURE
Testing procedures have been divided into
two headings namely bentonite models and
dredged sediment models.
6.1 For bentonite models
30 kg. of Enagi sand and 3 kg. of bentonite
inter-bedding each other were mixed with 18
kg. of distilled water in an AICO mixer, under
de-aired condition of -76 cm. Hg for 9 hours.
The reason for mixing under de-aired condition
was to avoid entrapping of air bubbles, which
have detrimental effect of forming the
pockmarks during the consolidation of clay
slurry (Gronow et al. 1988). Total amount of
0.001 0.01 0.1 1 10 100
DIAMETER (mm)
0
20
40
60
80
100
FINE MEDIUM COARSE
CLAY SILT GRAVELSAND
BR Soil
SF Sand
P
E
R
C
E
N
T
 P
A
S
S
IN
G
 (
%
)
Figure 2 Grain size distributions of Sao Francisco and Bento Ribeiro sands
302
slurry poured into the Mini-Drum was kept the
same in both the model tests. The acceleration
of drum was increased in stages to avoid
tensile cracking of bentonite layer. Due to the
centrifugation, bentonite and sand were
separated in uniform layers. After primary
consolidation, solutions of chemical were
poured over the bentonite layer through the
ring channel. Migration test were carried out at
105-g. Effective stress at the bottom of the
bentonite in both cases was calculated as 6.1
kPa (Table 3). One hour after pouring the
solution, a drainage valve was opened.
Discharged solutions were collected at regular
intervals and analyzed by high performance
liquid chromatography for determining the
relative concentration of discharged solution.
Model tests were terminated once the
discharge was no longer monitored due to the
decrease in hydraulic head. High Performance
Liquid Chromatograph (HPLC) was used for
the chemical analysis of solution discharged
from the Mini-Drum to obtain the
breakthrough curve for each chemical.HPLC
consists of solvent delivery unit, UV detector
and chromatopac. Solvent delivery unit
supplies the mobile phase under pressure to the
HPLC column, which is designed to retain the
different chemicals for different periods. The
chemicals from HPLC column then flow to
UV detector, which uses deuterium lamp as a
light source, and perform the ultraviolet
analysis and relay the test data to chromatopac
for printing the test results. The linear
adsorption coefficients (k) for both the
chemicals on bentonite were determined from
the classical batch experiments. In each batch,
1 g of bentonite was mixed with 12 mL. of
freshly prepared chemical solution (same
concentration as in centrifuge model) and
shaken for 24 hours giving adequate time for
adsorption.
Table 3. Model test conditions
Models g-levels sv’ (kPa)
Bmin 105 6.10
SALIcid 105 6.10
SF 50 22.7
BR 50 25.4
6.2 For dredged sediment models
Two centrifuge model containers with
dimensions of 21 cm. (width) x 25.8 cm.
(length) x 17cm. (height) were mounted in
opposite sides of the ring channel, which
allowed the drum centrifuge to be used as
beam type centrifuge. However, the whole area
of the ring channel can be used for modelling
geotechnical events as in the case of Hiroshima
University one. In the present study, this beam
type of facility was used to reduce the volume
of the soil models, so that about 20 pore
volumes of solution could flow through the
soil models during the observation time. A
piece of geotextile, having the same plan area
as that of the model container, was placed at
the bottom of the model container to allow
adequate drainage. Above this geotextile, a 5-
cm deep soil model was compacted in five
layers. In each layer 60 blows of a 2.54-kg
hammer, falling from a height of 30.5 cm was
used for the compaction of model. Models
were compacted at their respective optimum
water contents to produce maximum densities,
as shown in Table 2. After compaction of a soil
model, the centrifuge was tilted from the axis-
horizontal mode to the axis-vertical mode with
the help of an electrically driven motor.
Centrifuge acceleration was then applied in
increments of 10-g steps up to 50-g. Following
this; tap water was supplied to the soil model
from the overhead water tank through an inlet
pipe, to saturate the model. Three pore
volumes of water were allowed to flow
through the soil models in an attempt to ensure
complete saturation. It is believed that the
accelerated flow flushed out all of the air
bubbles. After three pore volumes of water
flowed through the soil, the zinc solution was
supplied to the soil model. 2 cm depth of zinc
solution was maintained constantly over the
soil model throughout the zinc migration
process. The 2 cm depth of zinc solution above
the soil model yielded a hydraulic gradient of
1.4 in an accelerated gravity field of 50-g. The
zinc solutions that migrated through the soil
models were collected regularly, and titration
of the samples were carried out immediately to
trace the breakthrough curve.
303
Table 4. Transport parameters for the models
Interstitial Velocity
 u (m/h)
Hydrodynamic
Dispersion, D (m2/h)
Name of model Tests
Model Prototype Model Prototype
Bmin 0.0032 0.300x10-4 5.90x10-5 5.90x10-5
SALIcid 0.0101 0.900x10-4 17.9x10-5 17.9x10-5
SF 2.2600 452.3x10-4 0.085 0.0017
BR 0.3870 77.40x10-4 0.030 0.0006
After attaining equilibrium of a
breakthrough curve, the zinc solution was
stopped and tap water was supplied to the soil
model to cleanse zinc from the soil model, in
order to obtain the desorption part of the
breakthrough curve. However, in the present
study only the absorption results have been
presented, as the numerical simulation was not
carried out for the desorption studies. The
cleansing process was carried out until the
relative concentration of effluent dropped to
below 2%. Effective vertical stresses at the
bottom of the soil model were calculated to be
22.7 kPa, and 25.48 kPa for SF and BR soil
models, respectively.
7. RESULTS AND DISCUSSION
7.1 Bentonite soil models
Each soil model was prepared in the same
way and therefore is the replicate of each
other. As this is the first attempt to model the
chemical flow using the Mini-Drum centrifuge,
emphasis here is centred at the validation of
transport phenomena by comparing the
breakthrough curves obtained from the model
tests and theoretical advection-dispersion
equation. Theoretical breakthrough curve for
each of the chemicals was calculated by
considering the bentonite layer only without
considering the underlain sand layer because it
is the bentonite that is effective in attenuating
the chemicals.
For the theoretical model, relative
concentration i.e. effluent concentrations
divided by the initial concentration of the
chemical solution (C/Co) was calculated by
using Eq. (6) and the average interstitial
velocity (u) and advection-dispersion
coefficient (D) was calculated by using Eq. (7).
The prediction of BNmin breakthrough curve
by the theoretical model is shown in Figure 3
where good fit between theoretical and
centrifuge models can be observed. The u and
D for this model were calculated as 3.2x10-3
m/h and 5.9x10-5 m2/h, respectively. Similarly,
the prediction of theoretical model for the
SALIcid is presented in the Figure 4 and is in
good agreement. Toward the end, the
theoretical model over-predicts the SALIcid
values, which is believed to be due to the
reaction between salicylic acid and bentonite,
as the discharged solution never showed the
initial concentration of 0.96 g/L. The
convection-dispersion parameters for this
model was calculated as u = 10.1x10-3 m/h and
D = 17.9x10-5 m2/h. These values are about 3
times greater than the corresponding values of
BNmin. These higher values of u and D are
believed to be due to the higher molecular
weight of the salicylic acid (Table 1.) which
make the flow faster under the accelerated
gravity field. The peclet number (Pe) of these
two models were calculated to be less than
unity hence, the model values of D have been
reported as the corresponding prototype values
of D in Table 4. However, the values of u and
D in both the cases are very low (nominal),
which may suggest that bentonite have good
potential in attenuating the tested organic
chemicals.
7.2 Dredged material models
Data from the centrifuge tests on Sao
Francisco sand and Bento Ribeiro sand are
presented in Figures 5 and 6. The diagrams
shown are for relative concentrations versus
elapsed time, where relative concentrations are
the measured effluent concentrations divided
by the initial concentration. The interstitial
velocity of the Sao Francisco soil model was
found to be nearly six times higher than that of
the Bento Ribeiro soil model (Table 4) and is
304
due to the high fines content in Bento Ribeiro
soil. Note that Sao Francisco soil has almost
zero clay content.
0,0
0,2
0,4
0,6
0,8
1,0
1,2
0,0 10,0 20,0 30,0 40,0 50,0
Time (Hours)
R
el
at
iv
e 
co
nc
en
tr
at
io
n
FITTED OBS
u = 0.03x10-3 
m/hour
D = 0.5x10-4 m2/hour
Rd = 2.5
Fig. 3 Breakthrough curve for Benzyl amine
The centrifuge data were analysed by the
computer code CXTFIT, a non-linear least-
squares routine designed to provide one or
more parameters for a number of transport
equation formulations (Parker and van
Genuchten, 1984). Two parameters, the
dispersion coefficient (D) and the retardation
factor (Rd), were simultaneously obtained
using CXTFIT. The breakthrough curves from
these centrifuge model tests have been well
fitted by the CXTFIT code as shown in Figures
6 and 7 for Sao Francisco sand and Bento
Ribeiro soil respectively.
The regression coefficient r2 obtained for
each test shown in Figures 6 and 7 indicates
the quality of the fit for the centrifuge data by
usingCXTFIT. The equilibrium model
describes the shape of the breakthrough curves
quite well. In present case N=50 and Pe is 29.1
and 169.7 for the test with Bento Ribeiro and
Sao Francisco soil respectively. The interstitial
velocity and hydrodynamic dispersion in the
test, in term of both model and prototype
values, have been presented in Table 4. The
ispersion coefficient of Sao Francisco soil is
higher than the dispersion coefficient of Bento
Ribeiro soil showing the dependence of the
dispersion coefficient with interstitial
velocities for the high Peclect numbers used.
The calculated value of retardation factor (Rd)
for Bento Ribeiro clayey sand was found
greater than the Rd of Sao Francisco sand.
0,0
0,2
0,4
0,6
0,8
1,0
1,2
0,0 2,0 4,0 6,0 8,0 10,0 12,0 14,0
Time (Hours)
R
el
at
iv
e 
co
nc
en
tr
at
io
n
FITTED OBS
u =0.09x10-3 
m/hour
D = 0.1x10-4 m2/hour
Rd = 8.1
Fig. 4 Breakthrough curve for Salicyclic 
acid
0,0
0,2
0,4
0,6
0,8
1,0
1,2
0,0 0,2 0,4 0,6
Time (Hours)
R
el
at
iv
e 
co
nc
en
tr
at
io
n
OBS FITTED
u = 4.5 x 10 -3 m/hour
D = 85.7 x 10 -3 
m 2/hour
Fig. 5 Breakthrough curve for zinc (SF sand)
8. CONCLUSION
In this study, Mini-Drum centrifuge facility
available at Hiroshima University and Federal
University of Rio de Janeiro were used to
investigate the migration of benzyl amine,
salicylic acid and zinc through clayey and
sandy soil models respectively. Predictions of
1-D advection-dispersion theoretical model
and the computer code CXITFIT are in good
agreement with the centrifuge test results and
thus validate the migration phenomena through
clayey and fine grain soil in the accelerated
gravity field. This shows that Mini-Drum
centrifuges can be a useful tool in modelling
pollution migration problems related to
geotechnical engineering.
0,0
0,2
0,4
0,6
0,8
1,0
0,0 1,0 2,0 3,0
Time (Hours)
R
el
at
iv
e 
co
nc
en
tr
at
io
n
OBS FITTED
u = 7.7 x 10 -3 m/hour
D = 30.5 x 10 -3 
m 2/hour
Fig. 6 Breakthrough curve for zinc (B R sand)
305
Benzyl amine treated bentonite shows about
three times lower interstitial velocity than
salicylic acid treated bentonite. Consequently,
dispersion coefficient of benzyl amine is lower
than salicylic acid. This difference in behavior
may be attributed to higher affinity of benzyl
amine to water and lower molecular weight of
benzyl amine than salicylic acid.
Both the interstitial velocities and
dispersion coefficients for benzyl amine and
salicylic acid are much smaller than the
corresponding values of zinc. Although the
organic compounds were migrated at the
acceleration level of 105-g compared to 50-g
for the zinc migration. This phenomenon
suggests the importance of clayey soil in
attenuating the migration of pollutants.
Furthermore, the interstitial velocity of the São
Francisco sand is six times greater than the
interstitial velocity of the Bento Ribero soil.
Similarly, the dispersion coefficient of the São
Francisco sand is also greater than the
dispersion coefficient of the Bento Ribero
sand. This difference in behavior is due to the
higher percentage of clay content i.e. 28 % in
Bento Ribero sand than the 0 % of clay content
in São Francisco sand.
9. REFERENCES
Almeida, M.S.S., Barbosa, M.C., and
Casanova, F., and M.C. Moreira Alves
(1998), “Characterization of the sediments
of Jacarepaguá lagoons for dredging
purposes”, 3rd Intern. Congress on
Environmental Geotechnics, Vol. 1 , pp. 69-
76, Lisboa, Portugal, 7-11 de Setembro de
1998.
Almeida, M.S.S., Borma, L. S. and Barbosa,
M.C., (1999), “Land Disposal of Dredged
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