Presentation made at the International Conference on Emerging Trends in Engineering, (ICETE 2012), NMAM Institute of Technology, Nitte, Karnataka State, India, 15th and 16th May, 2012.

1. THE SYSTEM DYNAMICS MODELING
METHOD IN APPLICATION OF
GEO-MEMBRANES AS LANDFILL
LINERS
By
Samson O. OJOAWO, Ph.D
Department of Civil Engineering,
Ladoke Akintola University of Technology Ogbomoso,
Nigeria

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

3. INTRODUCTION
*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

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

5. Figure 1. Schematic diagram of a liner system in landfills

6. * Geo-membranes = highest durability of
between 50 to 65 years (Rowe and Rinal, 2008)
* 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

7. CENTRAL AIM
To model the applications of Geo-
membranes as landfill liners using case
study of Ogbomoso North Local
Government Area (LGA) of Oyo State
Nigeria, in Africa

8. The Case Study
• Ogbomoso North LGA, Oyo State
Nigeria, in Africa & has an average
population of 198,720 (National Population
Commission, 2011)
• It lies on Long 40 15’East, Lat 80 07’ North
• It’s situated in the transitional zone
between rain forest and savannah region
(Edward and Joel, 1998)

9. Figure 2. Map of Africa showing Nigeria

10. Figure 3. Map of Nigeria showing the 36 States

11. Figure 4. Map of Nigeria showing Oyo State & Ogbomoso North LGA

12. Figure 5. Map of Oyo State showing the 33 Local Govt Areas (LGA)

13. Figure 6. Map of Ogbomoso North LGA, the Study Area

14. METHODOLOGY
(a) Materials studied:
Smooth HDPE
Textured HDPE
Smooth LDPE
Textured LDPE

15. Figure 7 . Sample of the Smooth HDPE

16. Figure 8 . Sample of the Textured HDPE

17. Figure 9 . Sample of the Smooth LDPE

18. Figure 10 . Sample of the Textured LDPE

19. (b) Properties considered:
Hydraulic conductivity
Porosity
Thickness
Maximum slope

20. (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)

21. 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

22. (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)

23. (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)

24. (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

25. 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 11. The Stella flow diagram of the system

26. (e) Validation of the model:
Through assessment of practical
problems of leachate pollution
containment with Geo-membranes
of Ogbomoso North LGA

27. Material Hydraulic
Conductivit
y
(x 10-9) m/s
Porosity Thickness
(m)
Maximu
m slope
Smooth
HDPE
0.58 0.62 0.004 16
Textured
HDPE
0.93 1.75 0.005 16
Smooth
LDPE
0.81 2.27 0.002 16
Textured
LDPE
1.16 1.85 0.003 16
TABLE I: VALIDATION DATA FOR THE GEO-MEMBRANE SAMPLES

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

29. 10:33 PM Sun, Apr 15, 2012
Fig 12. Breakthrough time graph of Smooth HDPE
Page 1
0.00 25.00 50.00 75.00 100.00
Time (yrs)
1:
1:
1:
23526458
23526458
23526458
1: Selected Breakthrough Time
1
1
1
1

30. 10:44 PM Sun, Apr 15, 20
Fig 13. Breakthrough time graph for Textured HDPE
Page 1
0.00 25.00 50.00 75.00 100.00
Time (yrs)
1:
1:
1:
10190915
10190915
10190915
1: Selected Breakthrough Time
1
1
1
1

31. 10:47 PM Sun, Apr 15, 2012
Fig 14. Breakthrough time graph of Smooth LDPE
Page 1
0.00 25.00 50.00 75.00 100.00
Time (yrs)
1:
1:
1:
10194942
10194942
10194942
1: Selected Breakthrough Time
1
1
1
1

32. 10:50 PM Sun, Apr 15, 2012
Fig 15 . Breakthrough time graph for Textured LDPE
Page 1
0.00 25.00 50.00 75.00 100.00
Time (yrs)
1:
1:
1:
10185531
10185531
10185531
1: Selected Breakthrough Time
1
1
1
1

33. Material Breakthrough
time (s)
Breakthrough
time (day)
Smooth HDPE 23,524,658 273
Textured HDPE 10,190,915 118
Smooth LDPE 10,194,942 119
Textured LDPE 10,185,531 117
TABLE II
BREAKTHROUGH TIMES OF THE STUDIED GEO-MEMBRANES

34. FINDINGS
*Smooth HDPE has the highest
simulated retention capability
for the leachate volume
----- this is explainable by the fact that of the 4 samples,
Smooth HDPE possesses the lowest water absorption rate
[Dauda & Salami, 2012]

35. **The texture LDPE on the other
hand recorded the lowest
breakthrough period

36. CONCLUSIONS

37. *effectiveness of the studied geo-
membrane material liners is of
the order
Smooth HDPE > Smooth LDPE >
Textured HDPE > Textured LDPE.

38. **The longest breakthrough period
discovered for the application of
geo-membrane liners in Ogbomoso
North LGA of Nigeria was 273 days
(3/4 year)

39. RECOMMENDATION

40. ***For landfill leachate
containment in the study
area, Smooth HDPE liners
are recommended

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

42. REFERENCES
[1] S.O Ojoawo “Management of leachate pollution form dumpsites in ogbomosoland”. Unpublished
Ph.D Thesis, Faculty of Technonoly, University of Ibadan, Ibadan, Nigeria, pp 51-52, 2009.
[2] J.T Pfeffer “Solid waste management in Engineering”. Prentice Hall, pp 235 -249, 1992.
[3] R.K Rowe “Geosynthetics and the minimization of contaminant migration through barrier systems
beneath solid waste” Proceedings of the 6th International Conference on Geosynthetics, pp 24 -36, 1998.
[4] L.H Kerry, A.D Christy, J.E Heimlich and K.L Shah “ Basics of Solid and Hazardous Waste Management
Technology”. Prentice Hall, Upper Saddle River, New York. Pp 45-46, 2005.
[5] R.K Rowe, E.T Kerry, L.M Quigley, M.A Robert, F.J Brachman, W.I Richard, J.M Booker, and R.I
John, 2nd ed., (2004) “Barrier Systems for Waste Disposal Facilities” . Prentice Hall, pp 22-25, 2004.
[6] J.O Wesseloo, A.T Visser and E.H Rust “A Mathematical Model for the Strain Rate Dependent
Stress-Strain Response of HDPE Geomembranes”. Geotextiles and Geomembranes 22, No.7: 273-295, 2004.
[7] M.W Sharma, G.J Hari, D.V Reddy and O.P Krishna “Geoenvironmental Engineering: Site
Remediation”, Waste Containment and Emerging Waste Management Technologies. John Wiley Sons, Inc,
Hoboken, New Jersey, pp 23-24, 2004.
[8] U.S Environmental Protection Agency, Office Municipal Solid Waste Disposal 2011.
[9]Gundle Lining Systems. GSE Lining Technology. [Brochure]. Gundle Lining Technology Inc., pp 27-
36, 1996.
[10] R.K Rowe and G.J Rinal “Durabiltiy of Landfill liners”. Prentice Hall, pp 4-6, 2008.
[11] NPC “Official gazette for 2006 population cencus”. National Population Commision. Nigeria, p 34,
2006.
[12] B. Edward and L.M Joel “World Atlas”. 16th ed., USA, pp 21-35, 1978
[13] E. Safari and C. Baronian “ Modelling temporal variations in leachate quantity generated at
Kahrizah landfill”. Proceedings of International Environmental Modeling Software, 482 – 484, 2002.
[14] T. Kadlec and M. Knight “Leachate management in landfills”. Environmental Hydrology, Chapter 12,
94 – 105, 1996.
[15] R.J Petrov and R.K Rowe “ Geosynthetic clay liner: chemical capability by hydraulic conductivity
testing and factors impacting its performance”. Canadian Geotextile Journal, 34: 863-885, 1997.
[16] J. Dauda and B. Salami “ An investigation into the physical properties of landfill liners”.
Unpublished B. Tech Project Report, Department of Civil Engineering, Ladoke Akintola University of
Technology, Ogbomoso, Nigeria, pp 56-59, 2012

43. THANK YOU
ALL FOR THE
ATTENTION