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Md. Tauhid-Ur-Rahman, 2009. An Investigation of the Contaminant Transport from the Waste Disposal
Using
ISSNSite,
0126-2807
Femlab.
Volume 4, Number 2: 79-88, May-August, 2009
© T2009 Department of Environmental Engineering
Sepuluh Nopember Institute of Technology, Surabaya
& Indonesian Society of Sanitary and Environmental Engineers, Jakarta
Open Access

Research Paper

AN INVESTIGATION OF THE CONTAMINANT TRANSPORT FROM THE WASTE
DISPOSAL SITE, USING FEMLAB
MD. TAUHID-UR-RAHMAN
Department of Civil and Environmental Engineering, Shahjalal University of Science and Technology,
Sylhet-3114, Bangladesh.
Phone: +88-0821-71349 extn-169; Fax: +88-0821-715257; E-mail:
Received: 4th April 2009; Revised: 15th May 2009; Accepted: 28th July 2009

Abstract: Untreated landfill leachate produced typically at the unmanaged waste
disposal site may pose substantial contamination hazards not only to the nearby
surface water but also to the groundwater system. This study attempts to focus on the
potential risk arising with the spreading of contaminant generated at the solid waste
disposal site in the lake Kiyanja watershed which has usually been considered as the
key source of supplying water to the surrounding community of the Masindi district of
Uganda. A numerical model was developed with the help of FEMLAB to study the
transport of the leached contaminants from the waste disposal site through the
subsurface soil. The model shows that the contamination plume needs around 40
hours to infiltrate through the saturated groundwater after being released from the

source. Further, it needs at least 183 hours to reach close to the nearby lake water.
Although, the deep groundwater currently seems to be protected, but it needs
adequate attention while installing deep wells through the clay layers to make it
remained safe for the future. It can however be mentioned that to protect and preserve
the groundwater resources, the waste disposal site should immediately be relocated
elsewhere.
Keywords: Numerical model, groundwater-pollution, leachate, unmanaged solid waste

INTRODUCTION
Urban landfill, due to its relatively lower maintenance cost, has popularly been choosing for
disposing finally the solid waste produced at any city dwellers, over the decades [1]. Well
maintained and scientifically designed landfill could significantly reduce the solid waste burden of
any urban community. However, unmanaged solid waste usually disposed in this landfill has
increasingly been becoming as one of the sources of potential environmental concern in most of
the developing countries [1,2]. Most of the pollution hazards that can likely be taken place at any
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Journal of Applied Sciences in Environmental Sanitation, 4 (2): 79-88.


Md. Tauhid-Ur-Rahman, 2009. An Investigation of the Contaminant Transport from the Waste Disposal Site, Using
Femlab.

uncontrolled waste disposal site are such as air pollution due to the spreading of bad odour,
potential public health risk since this landfill can be a breeding host for the disease causing
vectors and also the water pollution due to the subsurface transport of leachate [3-8].
The study site, Masindi District is located in the northernmost part of the western region of
Uganda. It is bordered by Luwero and Kiboga districts in the south, Hoima district and the
Democratic Republic of Congo in the west, while in the north it is bordered by the districts of
Gulu, Apac and Nebbi (Fig 1). It extends between 1°21′ to 2°24′ in the North and 31°18′ to 32°21′
in the East.

MASINDI
TOWN
LAKE
KIYANJA

Fig. 1: Map showing the location of Masindi district along with that of the lake Kiyanja
The District comprises four counties namely Kibanda, Buliisa, Bujenje and Buruli. It has a total
area of 9,326 sq. km (8,458 sq. km of land and 868 sq. km of water bodies), much of which is
gazetted as conservation area. The population of this Masindi District has increased steadily over
the years, from 155,511 in 1969 to 223,230 in 1980 and 260,796 in 1991, up to the present level
of 469,865 persons (National Census 2002). This district is largely rural, with more than 90% of
the population living in rural areas and depending on arable land and livestock farming. Fewer
than 10% of the district population live in the urban areas of Masindi Town Council, Kigumba
Town Council and Kijura (part of Masindi Town). Thus, the situation indicates a low level of
urbanisation in the district. The settlement patterns in the rural areas have also been greatly
influenced by geographical factors of terrain, climate, vegetation, disease agents and the physical
socio-economic infrastructure like roads, water supply and the different forms of land ownership.
The community water supply system of this town has never been well appreciated. Due to the
lack of well constructed water supply facilities, people have generally been collecting their water
required for domestic as well as drinking purposes from the boreholes that were constructed
around the community (Fig. 2C)
Like other cities in developing countries, Masindi in Uganda doesn’t have any sanitary landfill
to cope with the ever increasing solid waste disposal demand. As a consequence to this, solid
waste has always been disposed near the household premises (Fig. 2A, B). Leachate
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Journal of Applied Sciences in Environmental Sanitation, 4 (2): 79-88.


Md. Tauhid-Ur-Rahman, 2009. An Investigation of the Contaminant Transport from the Waste Disposal Site, Using

Femlab.

subsequently produced at this waste disposal site may easily get worst while it mixes with the
surface runoff. The subsurface Infiltration of this landfill leachate appears to be a potential source
that may cause substantial pollution to the surface water as well as groundwater resources [7-9].
Moreover, organic humic acid which forms in the intermediate stage can even cause severe
problem for the aquatic lives due to the rapid oxygen depletion. Physical and mathematical
models capable of quantifying the different environmental consequences occurring continuously
around us, have been practising by the environmental modellers since long [7-9]. In addition,
numerical analysis has long been applied as a tool in solving the intricate mathematical problems
associated with any environmental study. FEMLAB a multi-physics based numerical modeling
package that can simply be utilized to simulate any physical progression related with any adverse
environmental incident [10].
A

B

C

Fig. 2: A typical solid waste disposal custom around the community premises (A); an unmanaged
solid waste disposal site (B); and boreholes used by the community people for collecting
their demanded water (C) [10,11].
The objective of this present study is to highlight the pollution possibility for the groundwater
of the lake Kiyanja watershed of Masindi, Uganda, that may take place with the spreading of the
highly organic contained leachate which has been generating continuously at the nearby solid
waste disposal site .
METHODOLOGY
A multi physics numerical modeling package FEMLAB was selected to capture the
hydrological processes that can explain the possible transport of waste disposal contaminant
transport in the subsurface layers. For this, FEMLAB Chemical Module coupled with Earth

Science Module had been utilised to solve the advective-dispersion equation. For specifying the
dimensions and physics of the flow domain Richard’s equation had been used. In order to
generate the geometry of flow domain, background grid had been formed.
In developing the physical environment of the model, three sub domain layers including their
dimensions and the physics of the flow domain were specified. Various characteristics of the
associated parameters were also assigned to the three different subdomains (Table 1, 2 and 3).
These could be categorised as subdomain-1 representing the bottom clay layer, subdomain-2
that stands for the intermediate sandy clay layer and the subdomain-3 expressing the upper
sandy- silt layer mixed with organic materials (Fig. 3). The hydraulic conductivity for the bottom

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Journal of Applied Sciences in Environmental Sanitation, 4 (2): 79-88.


Md. Tauhid-Ur-Rahman, 2009. An Investigation of the Contaminant Transport from the Waste Disposal Site, Using
Femlab.

layer (layer-1), intermediate layer (layer 2) and the upper layer (layer 3) were taken as 1*10-7 (m
s-1), 1*10-4 (m s-1) and 1*10-3 (m s-1) respectively based on the soil report of the Masindi district.
Table1: Parameters assigned to the subdomain layers
Rectangle 1
Rectangle 2
Width-12
Width 12
Height-0.4
Height 0.5
Position
Position
X-0
X-0

Y-0
Y (-1.0)

Rectangle 3
Width-12
Height 0.5
Position
X-0
Y (-1.4)

Table 2: Subdomian setting for the Richard’s equation (esvr)
Quantity
Value
Description
Constitutive relation Brooks and Corey
----------0.6, 0.005
Liquid fraction saturated and residual
θs, θr
1
Time scaling coefficient
οts
Storage term
Specific storage
-----------S
0
-----------Xf, Xp
4e-10, 1e-5
Compressibility of fluid and solid
Ks
1e-5

Saturated hydraulic conductivity
*Ks
1
Saturated permeability
Ar
1001
Anisotropy ratios
1000
Density liquid
ρf
Qs
0
Liquid source

Table 3: Subdomain setting for solute transport (flow and media)
1
οts
Flow Field
theta_esvR
θs
u
u_esvR
v
v_esvR
Qs
0

Time scaling coefficient
Flow volume fraction
X- velocity

y-velocity
Fluid source

Boundary conditions were specified to the different boundaries considered for the conceptual
model (Fig. 3). It can easily be seen that out of the 11 boundaries presented in Fig. 4, only the no.
4 and no. 6 should be recognized as internal boundary, while the no. 2 would be considered as
the bottom boundary and the no.7 and no.8 should definitely be thought as top boundaries. It can
also be mentioned that only the boundary no. 7 and no. 3 have the inward flux, whereas the
boundary no. 9 have seepage face. However, mixed condition existed at boundary no. 10 could
be noticed. However, rest of the boundaries except no. 2 have zero flux. Moreover, free drainage
occurs at the bottom boundary as the selected inward flux and the saturated hydraulic
conductivity might have balanced themselves.

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Journal of Applied Sciences in Environmental Sanitation, 4 (2): 79-88.


Md. Tauhid-Ur-Rahman, 2009. An Investigation of the Contaminant Transport from the Waste Disposal Site, Using
Femlab.

Fig. 3: Conceptual model showing different sub domain layers [10]

B-7

B-8
B-11

B-5
B-6
B-3

B-10
B-4

B-1

B-9
B-2

Fig. 4: Boundary conditions assigned to different layers
Considering steady state flow condition, the simulation was run to solve the Richard’s equation.
An initial value of a contaminant influx of 1*10-6 (m s-1) with an assumed concentration, C (0.015
kg/m3) at the inward boundary was considered in this study. At boundary no. 2, the out flow was
estimated as -6.88*10-12 (m s-1). This outflow value might be negligible in compare to that of the
influx boundary. The outflow at boundary no. 10 was estimated as 5*10-9 (m s-1).

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Journal of Applied Sciences in Environmental Sanitation, 4 (2): 79-88.


Md. Tauhid-Ur-Rahman, 2009. An Investigation of the Contaminant Transport from the Waste Disposal Site, Using
Femlab.

RESULTS AND DISCUSSION
The leachate that could have generated at the waste disposal site may get started to move
in different directions after being guided by the surface runoff. This leachate contaminant could
mainly reach to the subdomain-03 through the boundary no. 7 and then can continue flowing
through the unsaturated zone vertically. After that it can advance further till it reaches the
seepage boundary no. 9 due to the existence of the differential water head there. At this
boundary, the contamination carried by the soil pore water could try to exit the subdomain as an

out flux. A part of influx could also have entered through the boundary no. 3 in the form of either
seepage or lateral infiltration.
The simulation run for the solute transport model shows that after the first one hour of its
being released from the waste disposal site, the contamination starts to move through the
infiltration boundary no-7 (Fig. 5) towards the unsaturated zone of the upper top layer. Through
this layer it can easily be transported along the vertical as well as horizontal direction after being
adequately directed by the pore water velocity. The visualization of this numerical model also
shows that the contamination needs at least 180 hours to reach closer to the boundary no 10.
After 183 hours (Fig. 7), the pollutant just touches the out flux boundary and then tries to move
out of that. There hasn’t been observed any flow moving towards the bottom layer due to the
presence of the impermeable clay layer. It has also been observed that the water inside the
saturated layer would only get contaminated if the pollutant would have passed 40 hours of its
travel distance after being first released from the disposal site (Fig 6). This pollutant may continue
to move forward till it reaches the lake water. This would surely contaminate the lake water as
well as the other adjacent surface water sources. The shallow and intermediate groundwater in
the saturated layer-2 would already have contaminated by this pollutant.

Fig. 5: Pollutant infiltrates through the unsaturated layer just after 1 hour
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Journal of Applied Sciences in Environmental Sanitation, 4 (2): 79-88.


Md. Tauhid-Ur-Rahman, 2009. An Investigation of the Contaminant Transport from the Waste Disposal Site, Using
Femlab.

Figure 6: Pollutant reaches in the saturated layer after 40 hours

Fig. 7: Pollutant touches the exit boundary after 183 hours

However, the contaminant from the waste disposal site to the deep ground water lying

beneath the impervious clay layer will not be able to reach immediately unless there have cracks
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Journal of Applied Sciences in Environmental Sanitation, 4 (2): 79-88.


Md. Tauhid-Ur-Rahman, 2009. An Investigation of the Contaminant Transport from the Waste Disposal Site, Using
Femlab.

and fissures in that layer which may guide the pollutant infiltrating through that. Considering the
future protection, the landfill should immediately be stopped and attempts should also be made to
shift it in another farthest location with providing sufficient provisions for the bottom lining, top
covering, leachate collection system, gas collection system and time-to-time monitoring system.
At the same time, the soil that had already been affected should be treated with soil remediation
such as soil washing and biodegradation. The shallow ground water extraction should also be
stopped for a certain periods and the community should be supplied water either from the deep
ground water aquifer or from the treated surface water sources. Proper care in adequate sealing
should also be taken while installing deep groundwater wells so that there wouldn’t be any
leakage in the clay layer.
It can also be stated that the overall Masindi area would only be sustainable if the present
environmental degradation resulting from the waste disposal site would possibly be minimized as
soon as possible. However, if the area would be exploited further due to the rapidly progressing
of the urbanisation, then there may be a major risk for the soil and ground water being polluted
eventually. Moreover, to get rid of this risk, policy-makers, the urban planners, donor agency and
in fact the people who are living in this area should take collectively immediate decision to restore
the groundwater resources of the that concerned area.

CONCLUSION
A numerical model using the multiphysics FEMLAB has been explored in this present study
to forecast the vulnerability of the groundwater resources of the Masindi district. It has been
presented here that the shallow groundwater has already been polluted after getting mixed with

the spreading of the contaminant plume from the waste disposal site. The clay layer has been
serving as a barrier for the deep groundwater. However, the waste disposal site should
immediately be handled due to its synchronized adverse impacts on the groundwater resources.
Such type of contaminant spreading understanding gained from the numerical model will
obviously assist to select appropriate mitigation measures to save the groundwater in the
concerned locality.
Acknowledgement: The author would like to express his gratitude to Professor Roger Thunvik, Land and
Water Resources Department, KTH, Stockholm, Sweden for his great help during the completion of the
project assignment using FEMLAB for the Quantitative Hydrogeology course.
References
1.
Mwiganga, M. and F. Kansiime, 2005. The impact of Mpererwe landfill in Kampala–Uganda, on the
surrounding environment. Physics and Chemistry of the Earth, 30:744–750.
2.
Heyer, K.U. and R. Stegmann, 2002. Landfill management: leachate generation, collection,
treatment and costs. Available from: <>.
3.
Landfills: Environmental Problems, />probl.html Accessed on 10th March 2009.
4.
Landfills, Accessed on 12th March 2009.
5.
Landfills: Hazardous to the Environment, Accessed
on 15th march 2009
6.
Kulabako R., Thunvik R, Mnalubega M. and Soutter L, 2005, Hydrodynamic modelling of
subsurface flow and contaminant transport in a Peri-urban settlement in Kampala. Land and
water Resources Department, KTH, Stockholm, Sweden.

86
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Md. Tauhid-Ur-Rahman, 2009. An Investigation of the Contaminant Transport from the Waste Disposal Site, Using
Femlab.

7.
8.
9.

10.
11.

Kulabako, R., M. Nalubega Uganda and T. Roger, 2004. Characterization of Peri-Urban
Anthropogenic Pollution in Kampala, Uganda. 30th WEDC International Conference,
Vientiane, Lao PDR, pp. 474-482.
Kulabako, R. 2005. Analysis of the Impact of Anthropogenic Pollution on Shallow Groundwater In
Peri-Urban Kampala, PhD thesis, Land and water Resources Department, KTH, Stockholm,
Sweden.
Rahman, M.T., Buccheri, M., Baghbanan, A., Kizito, F., Kwarteng, O.A., and Ntiamoah, B. 2005,
Development of a Conceptual model and Numerical Modelling of Contaminant Transport for
the Lake of Kiyanja Cachment (Uganda-Africa), Report of Quantitative Hydrogeology
Course, submitted to the Land and Water Resources Engg. Dept. of Royal Institute of
Technology, KTH, Stockholm, Sweden.
FEMLAB 3, 2004, Earth Science Module Library, 2004, COMSOL AB.
Quantitative Hydrogeology, LWR, KTH, Stockholm, Sweden. />1B1635/QH/CourseHome/index.htm

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Md. Tauhid-Ur-Rahman, 2009. An Investigation of the Contaminant Transport from the Waste Disposal Site, Using
Femlab.

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