1. Assessment of Red Soil as Solid Waste Landfill Liner System
Mani Bhargava Reddy1
, Muthukkumaran K2
Student, National Institute of Technology, Tiruchirappalli - 620015,
Associate Professor, Department of Civil Engineering,
National Institute of Technology, Tiruchirappalli 620015, India, e-mail:email@example.com
This study evaluates the performance of the red soil and their mix with fly ash, bentonite and
kaolinite as a liner material that act as containment of landfill leachate. Permeability tests were carried
out on the black soil and red soil composites in the laboratory. The leachate used in the experiments
was collected from a landfill situated in the outskirts of Bangalore. The permeation of the potassium
through the media is analyzed by conducting batch studies and the diffusion coefficient and adsorption
coefficients were back calculated. These values were used to model the contaminant transport
considering a clay thickness of 1 m in POLLUTE. POLLUTE software was used to study the
variation in the concentration of the target contaminants over a period of 5 years. The permeability
values and diffusion coefficient values obtained from the experiments were used as inputs for
POLLUTE. The results of the study showed that the red soil with 10% bentonite whose average
permeability was 4.310x10-9
m/s was considered an effective substitute for clay liner. The predicted
concentration profiles by POLLUTE also indicated that the red soil with 10% bentonite sample was
able to reduce the potassium concentration from 19000 mg/l to 0 within a depth of 0.6m over a period
of 5 years.
Keywords: Landfill, Liner, POLLUTE, Permeability and Red soil
Landfills have been one of the most adopted Municipal solid waste disposal methods.
Landfilling as a practice has evolved over the years from the conventional type to the modern type.
The purpose of landfill is to separate the waste from the environment and prevent any kind of pollution
to air, water, soil and the organisms. The landfill system consists of cover system, liner system,
leachate collection and gas collection systems. Modern landfills are scientifically engineered
containment systems, designed to minimize the impact of solid waste such as refuse, trash, and
garbage on the environment and human health. The greatest threat to ground water posed by modern
landfills is leachate. Leachate consists of water and water soluble compounds in the refuse that
accumulate as water moves through the landfill. This water may be from rainfall or from the waste
itself. Leachate may migrate from the landfill and contaminate soil and ground water, thus presenting a
risk to human and environmental health.
Landfill liners are designed and constructed to create a barrier between the waste and the
environment and to drain the leachate to the treatment facilities. This is done to prevent the
uncontrolled release of leachate into the environment. The potential threat posed by the waste
determines the type of liner system required for each type of landfill. Liners may be described as
single (also referred to as simple), composite, or double liners. The design of the liner system plays a
vital role in the performance of a landfill. The use of clay as liners in the liner system has a significant
role in the containment of the leachate. In the past decades, researchers have worked on the factors that
influence the hydraulic conductivity of compacted clays used for liners and covers in waste
containment systems (Boynton and Daniel (1985), Kleppe and Olson (1985), Daniel and Benson
(1990) and Othman et al. (1994) by conducting laboratory and field hydraulic conductivity tests
2. The objective of this research is to investigate the performance of red soil and the mixtures of
red soil with fly ash, bentonite and kaolinite as a substitute for the clay liner in the liner system. In the
present study, different combination of red soil, fly ash, bentonite and kaolinite are made and their
permeability properties are studied. The landfill leachate indicates the presence of higher levels of
potassium which can have adverse effects on the health that needs to be removed. The distribution
coefficient and the diffusion coefficient obtained from the laboratory studies were used in the
mathematical modelling using software Pollute v7.
2. Materials and Methods
The municipal solid waste leachate used in this study was collected from Mavallipura landfill site in
Bangalore. The leachate was diluted in 1:100 ratio and used for permeability test. The characteristics
of municipal solid waste leachate are shown in Table.1.
Table 1. Characteristics of Municipal solid waste Leachate
Electric conductivity in mhos/cm 87000
TDS mg/L 56000
BOD mg/L 6700
COD mg/L 21500
Sulphates as SO4, mg/L 316
chloride as Cl mg/L 8942.35
Calcium as Ca, mg/L 92.18
Total alkalinity as CaCo3 mg/L 13200
Iron as Fe mg/L 11.16
Copper as Cu, mg/L -
Silver as Ag, mg/L -
Chromium as Cr, mg/L -
Cadmium as Cd, mg/L 0.82
Lead as Pb, mg/L -
Zinc as Zn, mg/L 1.67
Nickel as Ni, mg/L 6
Sodium as Na, mg/L 15062.5
Potassium as K, mg/L 18427.5
Nitrate as No3, mg/L 3068
2.2 Red soil: Red soil of Bangalore collected from the Campus of Indian Institute of Science (IISc),
Bangalore, India is taken as the main soil. The soil was air dried and sieved using 2mm sieve.
2.3 Fly ash: A fly ash of class “F” category procured from Raichur Thermal Power Station (RTPS), in
Karnataka, India, called Raichur Fly ash (RFA) was used in the present study. The fly ash used was
grey in color.
2.4 Bentonite and Kaolinite: Bentonite is a natural clay mineral and is found in many places of the
world and it belongs to 2:1 clay family. The basic structure is composed of two tetrahedrally
coordinated sheets of silicon ions surrounding by a sandwiched octahedrally coordinated sheet of
aluminum ions. The isomorphs substitution of Al3
in the tetrahedral layer and mg2
3. for Al3
in the octahedral layer results in a net negative surface charge on the clay. It has excellent
sorption properties and possesses sorption sites available within its interlayer space as well as on the
outer edges. Bentonite procured from Kolar region of Karnataka was used in the present study. The
commercially available kaolinite was used in this study.
2.5 Mix proportion and Permeability Test: The Red soil, fly ash, bentonite and kaolinite were
mixed in proportions and conductivity of the samples was measured using constant head method.
Table 2 shows the description of the soil samples with weight and density. The size of the soil
specimen as 4 cm diameter and 6 cm height. Leachate brought from the site was used in the
experiments. The moisture content of the soil samples were measured by drying in oven at a
temperature of 105 degree Celsius.
Table 2. Description of soil samples along with weight and density
Sample Description Weight (g) Density(g/cc)
Red soil 551 1.89
Red soil+ 10% FA 536 1.77
Red soil+ 20% FA 534 1.76
Red soil + 30% FA 534 1.76
Red soil + 2% Bentonite 542 1.79
Red soil + 5% Bentonite 560 1.85
Red soil + 10% Bentonite 551 1.82
Red soil + 5%Kaolinite 546 1.80
Red soil + 15%Kaolinite 540 1.78
Red soil + 10%kaolinite 542 1.79
Batch tests were conducted in order to determine the adsorption coefficient and the diffusion
coefficient. Figure 1 shows the experimental setup for the measurement of hydraulic conductivity.
Fig 1. Experimental setup for measuring the hydraulic conductivity
2.6 Column Experimental setup
Figure 2 shows the column setup for the measurement of hydraulic conductivity. The test
column has a diameter of 4 cm and soil height 26 cm. A porous plate of 1 cm was placed between the
leachate and soil sample. The height of the leachate in the tank was constantly maintained 20 cm. The
4. infiltrated volume was measured and replaced with the same volume of leachate to re-establish the
original level. The test run was conducted at ambient room temperature. Outlet valve was opened
when sample was saturated and the advection-diffusion test was performed. The outlet was closed in
order to have a no flow boundary at the bottom for the diffusion test. For both advection - diffusion
and pure diffusions test period was 15 days. The effluent samples were collected over a 3-day interval
and analysed for the parameters Ca2+, Mg2+, Na+ and K+. After completion of the test, the
contaminated clay liner materials were analysed. Approximately 10-15 g of the soil sample was placed
in a 100 ml distilled water was added to the conical flasks. The samples were placed in optical shaker
speed of 150-160 rpm. The sample was withdrawn from the shaker after one hour and the sample was
filtered through centrifuge apparatus at speed of 6000 rpm run for 3 minutes. All of the tests were
carried out at room temperature. The diffusion coefficient (D), retardation factor(R) found for single
liner system using equation 1.
C/C0 = [
C- Final concentration of the sample
Vs- Seepage velocity
C0- Initial concentration of the sample
t- Time taken
Z- Thickness of the column
De- Diffusion coefficient of the sample
R- Retardation Factor
The initial and final concentrations of the samples are obtained using the Inductively Coupled
Plasma Spectroscopy (ICP-OES) analysis. Considering advection and diffusion responsible for the
migration of contaminating ions, the diffusion coefficients are calculated. The thickness is equal to the
soil height of 26cm and effluent samples were collected after a time period of 3 days.
Fig 2. Column setup for the single liner system
2.7 POLLUTE v7 model description
The theory implemented by the POLLUTEv7 program, in its basic mode of operation, is described in
detail by Rowe and Booker (1991). According to this theory contaminant migration in one-dimension,
for an intact material is given by the equation 2.
= − − ( ) (1)
5. c = concentration of contaminant at depth z at time t,
D = coefficient of hydrodynamic dispersion at depth z,
v = groundwater (seepage) velocity at depth z,
n = porosity of the soil at depth z,
= dry density of the soil at depth z,
Kd = distribution/partitioning (sorption) coefficient
at depth z,
va = nv = Darcy velocity,
3. Results and Analysis
3.1 Permeability Results
Red soil and mixtures
The permeability of the red soil decreased with the addition of fly ash. The permeability of the red soil
was found to be 1.82x10-6
m/s. The permeability of the red soil and its mixtures reduced with time.
Red soil mixtures recorded lower permeability compared to red soil. The average permeability of red
soil and 10% fly ash was found to be 7.48x10-7
m/s. With the increase in fly ash content to 20 and 30
percent, the permeability recorded was further lower values equal to 4.36x10-7
Figure 4a shows the variation of permeability of red soil and red soil mixtures with time.
Fig 4a. Variation of permeability of red soil and red soil mixtures with time. Fig 4b. Variation of
average permeability of Red soil samples with 10%, 20% and 30% fly ash.
Similarly, the average permeability of different red soil composites were plotted. The average
permeability of the samples reduced with addition of fly ash. With increase in fly ash content,
the permeability reduced. The average permeability was found to be maximum in case of red
soil (2 x10-6
m/s) and it decreased for the red soil mixtures to 3 x10-7
m/s. Figure 4b shows the
variation of the average permeability of red soil and its mixtures.
Permeability tests were conducted on red soil mixtures with bentonite and kaolinite and the
permeability of the samples was found decrease as shown in figure 6a. The observed average
permeability values in case of red soil and 10% bentonite were 4.31x10-9
m/s and similarly, the
average permeability of red soil+ 5% bentonite was 5.15x10-8
m/s as shown in figure 5a. The rate of
decrease in the permeability values in case of red soil and bentonite mixtures was found to be less. As
the concentration of bentonite was increased the average permeability was found to decrease.
Permeability tests were done on Red soil and Kaolinite admixtures, the average permeability of Red
soil, 5% kaolinite was 5.67x 10-8
m/s and red soil along with 15% kaolinite was 4.63x10-9
6. 5a. 5b.
Fig 5a. Variation of permeability of red soil samples with 5% and 10% bentonite. Fig 5b.
Variation of permeability of red soil samples with 5% and 15% kaolinite.
The average permeability plots for 5 % bentonite, 10% bentonite, 5% kaolinite and 15%
kaolinite are shown in figure 6. It was observed that the average permeability decreased with
increase in percentage of bentonite and kaolinite. However comparatively, the average
permeability of 5% bentonite was lower than 5% kaolinite. Therefore, it is preferable to use
bentonite as an effective substitute in red soil composites.
Figure 6. Variation of average permeability of red soil samples with 5%, 10% bentonite and 5%,
3.2 Column experiment test results
The measurement of the initial concentration, final concentration and standard was completed by using
the Inductively Coupled Plasma Spectroscopy (ICP-OES) analysis. The diffusion coefficient and
distribution coefficient values were back calculated using the equations (1) and (2). Five samples
were selected based on the permeability results and the tests were conducted. The obtained results for
selected mixtures are presented in table 3.
Table 3. Distribution and diffusion coefficient values of the selected samples.
Parameter Red soil Red soil +
20% fly ash
Red soil +
Distribution Coefficient (ml/g) 1.58 2.32 3.56 4.54 2.86
Diffusion Coefficient (m2
/a) 0.246 0.0357 0.0492 0.0568 0.0505
7. 3.3 POLLUTE Results
POLLUTE version 7 was used for analysis of the migration of the contaminant potassium
through the soil material over a period of five years. The experimentally obtained values like the
diffusion coefficient, distribution coefficient and porosity are used in the analysis. The thickness of the
layer considered was 1 m. The input parameters considered for Pollute are given in Table 4. Figures
7(a-e) show the POLLUTE analysis results.
Table 4. Input parameters considered for Pollute.
Parameter Red soil Red soil +
20% fly ash
Red soil +
Distribution Coefficient (ml/g) 1.58 2.32 3.56 4.54 2.86
Soil Porosity 0.455 0.475 0.462 0.469 0.49
Dry Density (g/cm3
) 1.44 1.39 1.425 1.449 1.35
Thickness m 1 1 1 1 1
Source Concentration g/l 19 19 19 19 19
Base Concentration (g/l) 0.0042 0.0141 0.00006 0.00069 0.0036
Diffusion Coefficient (m2
/a) 0.246 0.0357 0.0492 0.0568 0.0505
Figure 7a) Red soil Figure 7b) Red soil +20% Fly ash
Figure 7c) Red soil + 30% Fly ash Figure 7d) Red soil +10% Bentonite
8. Figure 7e) Red soil +10% kaolinite
The results showed that in all the cases the concentration reduced to zero within a depth of 0.8m over a
period of five years. Red soil with 10% bentonite and red soil + 30% fly ash mixtures were able to
reduce the concentration of potassium to zero within a depth of 0.6 m over a period of five years.
Since the permeability of red soil + 30% fly ash was higher it cannot be considered as a feasible
option. Therefore it can be concluded that red soil with 10% bentonite as a red soil composite can be
used as an effective replacement of clay liners for landfill liner system.
In the present study red soil composites were studied for serving as a replacement for the clay layer in
the landfill liner system. The design of clay liner depends on parameters such as permeability,
porosity, diffusion coefficient and distribution coefficient. Permeability tests and column tests were
conducted on the black soil and red soil composites in order to check the suitability of these as a
replacement to the clay liner in the liner system. Though the permeability values for all the considered
samples were in the range of ≤ 10-7
cm/s as per CPCB standards for liners. Based on the permeability
results and the POLLUTE analysis, it is observed that the concentration profile of potassium was
reduced to zero at 0.55 m in case of red soil with 10% bentonite. Therefore, it can be concluded that
red soil with 10% bentonite can be used as an effective replacement for the clay liner in the landfill
The authors like to thank Dr Sivakumar Babu G L, professor, Department of Civil Engineering IISC
Bangalore for providing us an opportunity to work in IISC Bangalore and IISC for providing us with
the equipment necessary for completing the experiments.
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