Presentation made at the International Conference on Hydrology and Groundwater Expo, Hilton San Antonio Airport, Texas, U.S.A, 10th to 12th September, 2012.

1. THE SYSTEM DYNAMICS MODELING
OF GEOSYNTHETIC CLAY LANDFILL
LINERS
By
Samson O. OJOAWO, Ph.D
Senior Lecturer,
Department of Civil Engineering,
Ladoke Akintola University of Technology Ogbomoso,
Nigeria

2. OVERVIEW
PREAMBLE
INTRODUCTION
METHODOLOGY
RESULTS AND DISCUSSION
FINDINGS
CONCLUSIONS
RECOMMENDATION
CONTRIBUTION TO KNOWLEDGE
REFERENCES

3. Figure 1. Map of Africa showing Nigeria
PREAMBLE

4. Figure 2. Map of Nigeria showing the 36 States

5. Figure 3. Map of Nigeria showing Oyo State

6. Figure 4. Map of Oyo State showing the 33 Local Govt Areas (LGA)

7. INTRODUCTION
Solid Waste Management (SWM)
PRACTICE IN NIGERIA
(a) Determining factors
i. Location: urban, semi-urban & rural centres
ii. Income of residents: high, medium & low
iii. Education level: literates, semi-literates &
illitrates

8. (b) The practice
(i) Generation: per capita = between 0.4 and
0.5kg/day (Ojoawo, 2011)
(ii) Collection and Storage from source:
bucket, calabash, bin, etc
(iii)Transportation: compactor trucks

9. Figure 5 Typical waste collection bins in rural centres

10. Figure 6. Typical waste collection bin in Urban centres

11. (iv) Disposal of wastes in the study area:
- Indiscriminate dumping: rural areas, about 35%
of general practice
-Open burning: rural areas, about 25%
-Composting: rural areas, about 17%
-Incineration: urban centres, about 7%
-Landfilling: urban centres, about 2 in a state,
about 15%

12. Figure 7. Typical compactor truck in Urban centres (LAWMA, 2012)

13. Figure 8. Some waste collectors at work

14. Figure 9. Indiscriminate refuse dumping in a rural area

15. Figure 10. Typical aged dumpsite

16. Figure 11. Refuse dump near uncompleted buildings

17. Leachates
*Leachates result from excess water passing
through dumped wastes (Ojoawo, 2009;
Brachman, et.al 2004)
*Leachate control (Pfeffer, 1992)
: cover provision
: liner application
* Liners protect underground water

18. * Liners usually in double layers, Rowe et. al,
2004:
(a) Upper = leachate collection
(b) Lower = secondary check, back-up
• Types of liners: geosynthetic clay
geo-membranes
geonets
geotextiles
etc
* Paper focuses on geosnthetic clay liners

19. Figure 12. Schematic diagram of a liner system in landfills

20. * Geosynthetic Clay Liner (GCL)s were introduced in 1986 as barrier systems for
waste containment sites (Neil and Eddie, 2007).
* GCLs are also called Geosynthetic barriers- Clay (GBR-C).
* GCLs are rolls of factory fabricated thin layers of bentonite clay
sandwiched between two geo-textiles or bonded to a geomembrane
(VanZanten, 1986).
* When compared with clay it has lighter volume, light weight and is convenient to
install. The GCL is versatile, cost-effective, and thinner than Compacted Clay
Liners (GRI, 2011)
* Bentonite attracts positively charged water particles; thus, it rapidly hydrates when
exposed to liquid, such as water or leachate. As the clay hydrates it swells, giving
it the ability to “self- heal” holes in the GCL (USEPA, 2001)
* System dynamics model = one of the latest and comprehensive and is therefore
extensively applied in WM (Ojoawo, 2009)
*System dynamics modeling technique thus employed in this paper

21. CENTRAL AIM
To model the applications of GCL
using case study of the 5 Local
Government Areas (LGAs) of Oyo State
Nigeria, in Africa

22. The Case Study
• the Ogbomosoland LGAs: (a) Urban = Ogbomoso North
Ogbomoso South
(b) Rural = Oriire
Ogo Oluwa
Suurulere
•Ogbomosoland, Oyo State
Nigeria, in Africa & has an average
population of 657,417
(National Population Commission, 2006)
• It lies on Long 40 18’East, Lat 80 10’ North
• It’s situated in the transitional zone
between rain forest and savannah region
(Edward and Joel, 1998)

23. METHODOLOGY
(a) Material studied:
Geosynthetic Clay Liner

24. (b) Properties considered:
Water Absorption
Hydraulic conductivity
Porosity
Thickness
Slope

25. (c) Governing Equations:
(i) For leachate generation (Safari and Baronian, 2002)
N cells
LQnT (nΔt) = W4(t) – Wg(t) + Σ LQn( i, (n – i + 1) Δt
i = 1 -------(1)

26. where
LQnT = Accumulative amount of leachate
generated from the system
nΔt = No of waste cells at the given time
W4 = Overall mass of water entering or
leaving the dumpsite
Wg = Total water loss due to degradation
LQn = Overall leachate quantity generated
from a single cell
n & i = Counters
t = Breakthrough time of the liner
d = Thickness of the liner
α’ = Effective porosity
K = Coefficient of permeability and
h = Hydraulic head

27. (ii) Breakthrough time, t (Kadlec and
Knight, 1996)
t = d2α’ / K( d + h) ------(2)
where
d = thickness of the liner (m)
α’ = effective porosity
K = coefficient of permeability (m/s)

28. (iii ) Leackage rate through the liners
qi, also by Kadlec & knight, 1996:
qi = K [ 1 + y cos ϕ ]
d
----- (3)
where
K = coefficient of permeability (m/s)
d = liner thickness (m)
ϕ = the liner slope (measured in angles)
y = the leachate depth over liner (m)

29. (d) Computer programming and Simulation:
*V B language was employed in coding the equations
*Key elements of the Model were defined and quantified as
variables
*Relationships were formulated mathematically
*System dynamics structures applied in developing
the source codes
*Stock flow diagram of the system designed using
STELLA 9.1.4 software and simulation package

30. Population
Births
?
BirthRate
Death Rate
Deaths
?
Initial Field Capactiy
Runoff Coefficient
Total Precipitation
Chemical Reaction
Total Waste Generated
?
Initial Dry Weight of SW
Primary Leachate
Gas Generation Rate Increasing
?
Decay Process
Water Consumption DueTo Waste Decomposition
?
Mass of Water Consumed per CubicMeter of Ga Produced Decreasing
?
Effective Precipitation
Overall mass of WaterEntering or Leaving Dumpsite
?
Actual Evapotranspiration
?
Correction Factor
Overall leachate
Quantity for Single Cell
?
Field Capacity
?
Accumulative Amount of Lechate
?
Moisture Content of Waste
?
Estimated Population
Effective Porosity
Coefficient of Permeability
Hydraulic Head
Breakthrough Time
Saturated Vertical
Hydraulic Conductivity
Liner Slope in angle
Rate of Leakage
Thickness of Liner
?
Figure 13. The Stella flow diagram of the system

31. (e) Validation of the model:
Through assessment of practical
problems of leachate pollution
containment in the study area with
properties of Gesynthetic Clay
Liner materials

32. TABLE I: VALIDATION DATA
Material Hydraulic
Conductivity
(x 10-11) m/s
Porosity Thickness
(m)
Maximum
slope
Water
Absorption
(%)
GCL 5.0 0.62 0.005 2 475
Source: Petrov and Rowe (1997); USEPA, 2001b;
Sivakumar, et.al, 2001; Ojoawo, 2009

33. RESULTS AND DISCUSSION
On Simulation for 100 years the yearly
behavioural patterns are as shown below:

34. 9:43 AM Tue, Apr 24, 2012
Figure 14: Ogbomoso North LG- Breakthrough time graph
Page 1
0.00 25.00 50.00 75.00 100.00
Time (yrs)
1:
1:
1:
10164051
10164051
10164051
1: Selected Breakthrough Time
1
1
1
1

35. 9:54 AM Tue, Apr 24, 2012Page 1
0.00 25.00 50.00 75.00 100.00
Time (yrs)
1:
1:
1:
10163965
10163965
10163965
1: Selected Breakthrough Time
1
1
1
1
Figure 15: Ogbomoso South LG- Breakthrough time graph

36. 9:54 AM Tue, Apr 24, 2012
Fig 16: Oriire LG- Breakthrough time graph
Page 1
0.00 25.00 50.00 75.00 100.00
Time (yrs)
1:
1:
1:
7512343
7512343
7512343
1: Selected Breakthrough Time
1
1
1
1

37. 10:50 PM Sun, Apr 15, 2012
Figure 17 . Ogo Oluwa LG- Breakthrough time graph
Page 1
0.00 25.00 50.00 75.00 100.00
Time (yrs)
1:
1:
1:
6511145
6511145
6511145
1: Selected Breakthrough Time
1
1
1
1

38. 10:44 PM Sun, Apr 15, 20Page 1
0.00 25.00 50.00 75.00 100.00
Time (yrs)
1:
1:
1:
7324567
5
7324567
7324567
1: Selected Breakthrough Time
1
1
1
1
Figure 18: Suurulere LG- Breakthrough time graph

39. TABLE III
BREAKTHROUGH TIMES OF GCL IN THE 5 LGAs
LGA Breakthrough time (
x 107s)
Breakthrough time
( x days)
Ogbomoso North 1.0165 7.74
Ogbomoso South 1.0163 7.73
Oriire 0.7512 5.72
Ogo Oluwa 0.6511 4.99
Suurulere 0.7324 5.57

40. FINDINGS
*GCL has the highest simulated
retention capability for the
leachate volume in urban LGAs

41. **The least breakthrough time
of 5 days was recorded in Ogo
Oluwa LGA- a rural area

42. CONCLUSIONS

43. *effectiveness of the GCL materials
in leachate containment in the
study area is of the order
Ogo Oluwa < Suurulere < Oriire <
Ogbomoso South < Ogbomoso
North

44. **The simulated longest
breakthrough period discovered for
the application of GCL in
Ogbomosoland LGA of Nigeria was
8 days

45. RECOMMENDATION

46. ***GCL are recommended
for landfill leachate
containment in the Urban
LGAs of Ogbomosoland

47. CONTRIBUTION TO
KNOWLEDGE
* The model is universal and thus a
handy tool for dumpsite/landfill
leachate control world-wide

48. Acknowlegements
Mrs Olubunmi T. Ojoawo & Mr. Josiah Adelekan,
Software Assistants

49. REFERENCES
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51. THANK YOU ALL
FOR THE ATTENTION