This research was conducted to study exfiltration of wastewater from gravity sewers. Exfiltration through different types of sewer leaks were studied. With the different size of leakage areas and a constant thickness of soil bedding, it was found that the exfiltration rate reduces and became constant over a duration of one (1) to three (3) days. Knowing the exfiltration rate, the time

taken for the polluted water exfiltrate from sewer pipes to reach the groundwater can be determined so that preventive measures can be taken to prevent it. From studies conducted, it can be shown that the size of the leakage area was found to play an important role in determining the size of the clogging zone, the increased in the clogging zone resulted in the decreased of exfiltration rate due to the accumulation of organic matters at the edge of the leakage area and trapped in the pores of the bedding soil

Ab Wahab, Mohd Ashaari

Abdul Talib, Suhaimi

Baharom, Bahardin

Marwi, Mat Som

Universiti Teknologi MARA Institutional Repository

Volume 3  No. 2
Dec  2006
Institute of Research, Development and Commercialisation
ISSN 1675-7009
JOURNAL
Scientific
RESEARCH
 
 
 
SCIENTIFIC RESEARCH JOURNAL 
 
Chief Editor 
Prof. Dr. Zaiki Awang, 
Universiti Teknologi MARA, Malaysia 
 
 
Managing Editor 
Assoc. Prof. Dr. Razidah Ismail, 
Universiti Teknologi MARA, Malaysia 
 
 
Editorial Advisory and Review Board 
Prof. Dr. Ir. Wahyu Kuntjoro, Universiti Teknologi MARA, Malaysia 
Assoc. Prof. Dr. Salmiah Kasolang, Universiti Teknologi MARA, Malaysia 
Assoc. Prof. Ir. Dr. Muhammad Azmi Ayub, Universiti Teknologi MARA, Malaysia 
Prof. Dr. Ichsan Setya Putra, Bandung Institue of Technology, Indonesia 
Prof. Dr. Mohd. Nasir Taib, Universiti Teknologi MARA, Malaysia 
Prof. Dr. Ir. Shah Rizam Mohd. Shah Baki, Universiti Teknologi MARA, Malaysia 
Prof. Dr. Titik Khawa Abd. Rahman, Universiti Teknologi MARA, Malaysia 
Prof. Dr. Luciano Boglione, University of Massachusetts Lowell, USA 
Prof. Dr. K. Ito, Chiba University, Japan 
Prof. Dr. Azni Zain Ahmed, Universiti Teknologi MARA, Malaysia 
Prof. Ir. Dr. Ideris Zakaria, Universiti Malaysia Pahang, Malaysia 
Prof. Dr. Abd. Aziz Dato’ Abd. Samad, Universiti Tun Hussein Onn, Malaysia 
Prof. Sr. Ir. Dr. Suhaimi Abd. Talib, Universiti Teknologi MARA, Malaysia 
Assoc. Prof. Ir. Dr. Kartini Kamaruddin, Universiti Teknologi MARA, Malaysia 
Assoc. Prof. Dr. Hamidah Mohd. Saman, Universiti Teknologi MARA, Malaysia 
Dr. Robert Michael Savory, Universiti Teknologi MARA, Malaysia 
Assoc. Prof. Dr. Mohd Hanapiah Abidin, Universiti Teknologi MARA, Malaysia 
 
 
 
Copyright © 2006 Universiti Teknologi MARA, 40450 Shah Alam, Selangor, Malaysia. 
 
All rights reserved. No part of this publication may be reproduced, stored in a retrieval system or 
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Scientific Research Journal is jointly published by Institute of Research, Development and 
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The views and opinion expressed therein are those of the individual authors and the publication of 
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reproduce any part of this publication. 
 
 
 
 
 
 
SCIENTIFIC 
RESEARCH 
JOURNAL   
Vol. 3 No. 2                                 December 2006                     ISSN 1675-7009 
 
1. Development of an Automated Bi-axial Solar Photovoltaic 
Tracking System 
Ahmad Maliki Omar 
Muhamad Rizuan Yahir 
Sulaiman Shaari  
Abdul Rahman Omar 
 
1 
2. Bending and Bonding Properties of Sandwiched Polymer 
Concrete Composites 
Hamidah Mohd Saman 
Azmi Ibrahim 
Yakub Md. Taib 
Mohd. Faizal Md. Ja’afar 
 
13 
3. Ergonomics Analysis of Muscles Activity of Workers in a 
Metal Stamping Industry 
Md Fuad Bahari 
Abdul Rahman Omar 
Darius Gnanaraj Solomon 
Nor Hayati Saad 
Isa Halim 
 
31 
4. 
 
 
 
 
 
 
 
 
 
Optimisation of Calcium Silicate and Sand Cement Bricks in 
Masonary Bearing Walls 
Kartini Kamaruddin 
Siti Hawa Hamzah 
 
 
 
 
 
 
45 
 
 
 
 
 
 
 
 
 
 
 
 
 
5. 
 
 
 
 
 
 
Exfiltration from Sewers: Effects of Different Type of 
Leakage 
Mohd Ashaari Ab Wahab 
Suhaimi Abdul Talib  
Bahardin Baharom 
Mat Som Marwi 
 
 
 
 
 
61 
 
 
 
 
Exfiltration from Sewers: Effects of
Different Types of Leakage
Mohd Ashaari Ab Wahab, Suhaimi Abdul Talib,
Bahardin Baharom & Mat Som Marwi
Institute for Infrastructure Engineering and
Sustainable Management (IIESM)
Faculty of Civil Engineering
Universiti Teknologi MARA (UiTM), Malaysia
ABSTRACT
This research was conducted to study exfiltration of wastewater from gravity
sewers. Exfiltration through different types of sewer leaks were studied. With
the different size of leakage areas and a constant thickness of soil bedding, it
was found that the exfiltration rate reduces and became constant over a
duration of one (1) to three (3) days. Knowing the exfiltration rate, the time
taken for the polluted water exfiltrate from sewer pipes to reach the groundwater
can be determined so that preventive measures can be taken to prevent it.
From studies conducted, it can be shown that the size of the leakage area was
found to play an important role in determining the size of the clogging zone,
the increased in the clogging zone resulted in the decreased of exfiltration rate
due to the accumulation of organic matters at the edge of the leakage area and
trapped in the pores of the bedding soil
Keywords: Exfiltration, wastewater, gravity sewers, sewer leaks, clogging zone
Introduction
Sewerage system plays an important role in ensuring public health,
environmental protection and enhancing the standard of living of the general
population. Sanitary sewer systems are designed to collect and transport
61
Scientific Research Journal
ISSN 1675-7009
© 2006 Universiti Teknologi MARA (UiTM), Malaysia.
Vol. 3 No. 2, 61-69, 2006
62
Scientific Research Journal
to waste water treatment facilities the municipal and industrial waste
waters from residences, commercial buildings, industrial plants, and
institutions, together with minor or insignificant quantities of ground water,
storm water and surface waters that inadvertently enter the system [1].
Broken sewer and leakage pipes have been identified as one of the
major problems in sewer network management. Serious environment
damage and threats to the local community may result from sewage
being release into the soil and groundwater. This project is intended to
provide a clear understanding on the exfiltration behaviour so that
corrective and preventive measures can be recommended and
implemented.
Vollertsen and Hvitved-Jacobsen [2] conducted pilot scale
experiments on exfiltration of wastewater from gravity sewers. The effect
of storm events, flushing of pipes and alternating infiltration or exfiltration
were simulated in the experiments. Exfiltration through different types of
sewer leaks and into different soil beddings condition were also studied.
That mean, it can be estimate how long the exfiltration will polluted the
groundwater. The exfiltration was governed by the development of a
clogging zone at the sewer leak and could be characterized by a leakage
factor. The leakage factor may then be use to estimate the risk of
groundwater pollution from a sewer network. However, it is reasonable
to assume that when groundwater can infiltrate, wastewater may also
exfiltrate under given conditions.
On the use of TV-inspection for evaluating pollution due to leakages
from sewers, available literature agree that the method is inconclusive
when identifying if – and to what degree – wastewater leaking is from
sewers [3, 4]. In other words, not all damages of sewers are also leaks
from exfiltration. The goodness of this postulate is difficult to assess as a
missing correlation between the damages found by TV inspection and
exfiltration could also be due to difficulties in determination of exfiltration
[5].
The main objective of this study is to establish of an experimental
procedures for determining exfiltration from sewers due to different
leakage causes under various flow and to determine exfiltration from
sewers due to different sizes and faulty sewer fittings under various flow
and soil bedding conditions.
63
Exfiltration from Sewers: Effects of Different Types of Leakage
Experimental Set-up
Figure 1 shows the layout plan for the equipment used for the study of
exfiltration from various pipes. The equipment was set-up near an
operational aeration settling tank at Univesiti Teknologi MARA main
campus in Shah Alam. This circular aeration tank has a capacity to process
wastewater produced by approximately 3000 residence and non-residence
populations. A supply of fresh wastewater from inlet of the aeration tank
was pumped into a 150-gallon tank as shown in Figure 1. The wastewater
was allowed to flow into a 100-gallon tank before it flows under gravity,
through four sets of 110mm PVC pipes placed at a gradient of between
1.0 to 1.5 %. The flow rate of 0.3 m/s were maintained by controlling the
inlet valves.
Four 300 mm diameter by 750 mm height column reactors (marked
A, B, C and D in Figure 1) were placed under the pipes. Figure 2 and
Figure 3 show the cross-sections of one of the column reactor. A stainless
steel net with 1 mm openings was placed at the bottom of the column and
two layers of soil were laid on top of it consisting of a layer of gravel
underneath a layer of sand. The gravel was used to support and control
the thickness of the sand bedding and performed as an underdrain.
Different height of sand bedding can be simulated by varying the thickness
of the gravel and sand layers.
Figure 1 : Experimental Set-up for Exfiltration Experiment
X 
Valve to  
control flow 
Column Tank 
Ø300mm 
PVC pipe 
Ø110mm 
PVC pipe 
Ø110mm 
      
      
      
INLET 
             
             
OUTLET 
X 
X 
X 
Compact 
Ball Valve  
Pump 
 
100 Gallons 
Tank 
 
150 Gallons 
Tank 
                  
                  
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                  
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500mm 
500mm 
500mm 
A 
B 
C 
D 
64
Scientific Research Journal
Experimental Works
During the experiments, all the PVC pipes and the column reactors
described above were used. A hole is made underneath each pipe above
the reactor. Different size of hole is made in each pipe to simulate the
different sizes of leakage. In this study, three different sizes of leakage
and faulty fitting (Figure 2) were used. The three different sizes of leakages
are 10 cm2, 20 cm2 and 30 cm2. Sand bedding thicknesses of 200 mm
and 300 mm were used in the experiments.
Wasterwater was allowed to flow through each of the PVC pipes at
a constant rate of 0.15 ms-1 and 0.3 ms-1. The excess wastewater was
collected and discharged back into the aeration tank at the outlet.
Exfiltration from the leak in the pipe was allowed to flow through the
sand bedding an into the free-draining gravel layer. A funnel underneath
a column reactor then channeled the exfiltrated water into a measuring
cylinder. The volume of water collected in the measuring cylinder was
recorded with time. The exfiltration rate through the soil bedding were
measured for several days until the exfiltration rate became constant.
Figure 2: Faulty Sewer Fittings and Column Cross Section
Exfiltration 
Steel net of 
1mm 
BEAKER 
GRAVEL
SAND 
           
           
Ø110mm 
PVC PIPE                  Various Flow 
                                   V= 0.3 ms-1 and 0.15 ms-1 
           
           
Ø300mm 
1.5-2% 
    30mm 
DETAIL A 
Faulty Fittings 
DETAIL A 200mm 
200mm 10m
  10mm 
65
Exfiltration from Sewers: Effects of Different Types of Leakage
Results and Discussion
Effect of Leakage Areas on Exfiltration Rate
Figure 4 and Figure 5 show the results of test carried out to determine
the effect of different areas of leakage on exfiltration. The bedding
thickness and flow velocity adopted during these tests were 200 mm and
0.15 ms-1 respectively.
It is clearly evident that exfiltration from sewers can be described as
a three stage phenomena. The first stage which lasted over duration of
12 hours is characterized by a high and rapidly decreasing rate of
exfiltration. The exfiltration rates for the 10 cm2, 20 cm2 and 30 cm2
leakage areas were observed to have been reduced during this stage by
52 %, 68 % and 71 % respectively. This stage is the followed by a
further decreasing exfiltration rate over time. This decrease however is
much smaller compared to Stage I. By the end of stage II the exfiltration
rate observed were between 15 % and 25 % of the initial exfiltration
rate. Finally during stage III, exfiltration rate became stable and measured
exfiltration rates were 15 %-20 % of the initial exfiltration rates.
Different leakage areas affect only the initial amount of wastewater
exfiltrating from the sewer pipe. The large area of leakage tends to release
more wastewater into the soil bedding during stage I. However,
Figure 3: Wastewater Flow Variations
                                 
                                 
                                 
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  
  
 
 
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Sediment bed 
               
Water level 
variation 
Flow 
Ø110mm 
PVC pipe 
GRAVEL 
SAND 
Exfiltration 
Funnel 
66
Scientific Research Journal
Figure 4: Results of Tests Showing the Effects of Different Leakage
Areas on Exfiltration Rate
Figure 5: Idealised Results of Tests Showing the Effects of
Different Leakage Areas
0
2
4
6
8
1 0
0 1 2 3 4 5 6
T im e  (d a y)
E
xf
il
tr
at
io
n 
R
at
e 
(L
it
re
s/
da
y-4
1 0 c m 2 , 0 .1 5 m /s 2 0 c m 2 , 0 .1 5 m /s 3 0 c m 2 , 0 .1 5 m /s
 
0
0.2
0.4
0.6
0.8
1
0 1 2 3 4 5 6
Time (day)
U
ni
t
10cm2, 0.15m/s 20cm2, 0.15m/s 30cm2, 0.15m/s
Stage IIIStage IIStage I
irrespective of the sizes of the leakage areas the long term exfiltration
rates were similar. Thus is can be concluded that, leakage areas do not
have a significant effect on exfiltration rates. This can be attributed to
67
Exfiltration from Sewers: Effects of Different Types of Leakage
the fact that solid in the wastewater filled up the pores in the bedding
material, thus making it less and less permeable over time. The behaviour
can also be described as a “self sealing” leak.
In these tests, the three stage exfiltration phenomena prevailed.
Furthermore it was also observed that the duration of Stage I lasted for
12 hours. The results of these tests are as expected, i.e. thicker bedding
would result in lower exfiltration rates. This is due to the increase in the
flow path and increase in flow resistance, thus reducing the hydraulic
gradient required to drive the flow. During stage I, a reduction of 69 %
and 60 % of the exfiltration rates were observed for the 200 mm and 300
mm thickness soil bedding respectively. After 6 days the exfiltration the
200 mm thick bedding was measured to be 12 % of the initial exfiltration
rate, while in the 300 mm thick bedding, the exfiltration was virtually
sealed.
Effect of Faulty Fittings on Exfiltration Rate
Tests were also performed on a faulty pipe joint to determine the effects
of flow velocity and bedding thickness on exfiltration from sewers. Results
on effects of flow velocity and bedding thickness are shown in Figure 6
and Figure 7.
Figure 6: Results of Tests Showing the Effects of Flow
Velocity on Exfiltration Rate
 
0
1
2
3
4
5
6
7
0 1 2 3 4 5 6 7
Time (day)
Ex
fil
tra
tio
n 
Ra
te
 (L
itr
es
/d
ay
) x
 1
0-4
200mm,0.15m/s 300mm,0.15m/s
68
Scientific Research Journal
In both sets of tests, the three stage exfiltration behavior is clearly
distinct. As with the case of holes of different sizes, stage I of exfiltration
from a faulty fitting also lasted for a duration of 12 hours. The results
obtained from these two sets of tests seemed to suggest that both flow
velocity and bedding thickness do not have much influence on the
exfiltration rates from sewer pipes.
Conclusion
From the results, the following conclusion can be drawn.
1. The apparatus and experimental set-up designed in this study has
successfully enabled the exfiltration rates from sewer pipes to be
determined.
2. Overall findings of this project had shown that irrespective of the
study condition, the exfiltration rate behaviour can be described by a
3-stage process. Stage I involves a rapid decrease in exfiltration
rate. This stage lasted over duration of 12-24 hours. Stage II is
followed by a further reduction in exfiltration rate. However the
reduction in this stage (Stage II) is very much lower compared to
Stage I. Finally during Stage III the exfiltration rate becomes constant
and it is less than 10 % of the initial exfiltration rate.
Figure 7: Results of Tests Showing the Effects of Bedding
Thickness on Exfiltration Rate
0.00
0.50
1.00
1.50
2.00
2.50
3.00
0 0.5 1 1.5 2 2.5 3
Time (day)
Ex
fil
tra
tio
n 
R
at
e 
(L
itr
es
/d
ay
) x
 1
0-4
200mm,0.3m/s 300mm,0.3m/s
69
Exfiltration from Sewers: Effects of Different Types of Leakage
3. This study shows that the size of leakage affects only the amount of
exfiltration. A large leakage area leads to high amounts of exfiltration.
However if rates and flux are considered, leakage areas do not have
much effect on the exfiltration rates. Exfiltration rate becomes constant
after 3 days.
4. Further studies should be conducted to determine the effect of
different grading (of bedding material) on exfiltration rates and also
on the wastewater quality exfiltrated from sewers.
References
[1] Amick, R. S. and Burgess, E. 2000. Exfiltration in Sewer Systems.
National Risk Management Research Laboratory, 26.
[2] Vollertsen, J. and Hvitved-Jacobsen, T. 2002. Exfiltration from gravity
sewers – a pilot scale study. 3rd Int. Conf. on sewer processes
and networks, Paris, France, pp. 155-162.
[3] Eiswirth, M. and Hotzl, H. 1994. Groundwater contamination by
leaking sewerage systems. Water Down Under, November 1994,
Adelaide, Australia, pp. 21-25.
[4] Knudsen, L., Andersen, U., Orskov, P. and Pederesen, C. M. 1996.
Avoid drinking water pollution. Stands og havneingenioren, 10,
pp. 34-36.
[5] Ab-Wahab, M. A., Abdul-Talib, S., Baharom, B. and Marwi, M. S.
2004. Exfiltration from sewers pipes – Effects of flow rates, different
leakage area and soil bedding. 1st Asian Junior Scientists
Workshop on Sewer Network Processes and Urban Drainage,
Faculty of Civil Engineering, UiTM, February 7-10, Malacca,
Malaysia.


Exfiltration from sewers: effects of different types of leakage / Mohd Ashaari Ab Wahab ... [et al.]

http://ir.uitm.edu.my/id/eprint/12816/1/AJ_MOHD%20ASHAARI%20AB%20WAHAB%20SRJ%2006%201.pdf

Exfiltration from sewers: effects of different types of leakage / Mohd Ashaari Ab Wahab ... [et al.]

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