Siobhan Jackson - eWISA

INVESTIGATION OF SEEPAGE WATERS IN THE
ETHEKWINI MUNICIPALITY
Siobhan Jackson
Durban Metro Water Services, Wastewater Management Laboratory,
PO Box 1038, Durban, 4000. Tel: (031) 302 4796. Fax: (031) 302 4747.
E-mail: mailto:siobhanj@dmws.durban.gov.za
ABSTRACT
South Africa is acknowledged as a water scarce country and as such has to ensure that its water
assets are utilised effectively to ensure sustainability. Although the eThekwini Municipality lies in
the supposedly water rich province of KwaZulu-Natal, water stewardship is viewed with as much
concern here as it is in other more arid provinces of the country. Treated water travels through
approximately 12 000 km of mains distribution pipeline and sewage through more than 7 000 km of
major sewerage pipes in the municipality. Water could be lost from either network and a system
has therefore been put in place to try to establish the source of a seepage water before action is
taken.
Once a complaint of seepage has been received in the Call Centre, a plumbing team is sent out to
investigate and, if the cause of the problem is not immediately obvious, a chemical sample is taken
and brought back to the central laboratory for analysis. The presence of the major trihalomethanes
(THMs) is used as a primary indicator of potable water. These compounds may however, also be
found in sullage or grey water or in leaks from swimming pools. When there is doubt as to the
identification of the water source, a second team of samplers from the laboratory is sent on site to
take both chemical and bacteriological samples. In this way, costs to Water Operations are
reduced, as effort is not put into tracing and digging seepages which turn out to be normal ground
water. In addition, leaks of potable water traveling over some distance, which might otherwise have
been considered as ground water, can be identified.
INTRODUCTION
During the 1980s the then Durban Water Services started trying to identify the source of seepage
waters in order to optimise the use of digging and plumbing teams and reduce the amount of water
lost in the system. At the start, a range of chemical and bacteriological tests was used and several
days were necessary to complete the analyses and produce a result. Over the years, the testing
has been refined and reduced to the present system where results are often available within hours
of the sample having been taken.
When a complaint of a seepage water is received in the Call Centre, the job is given a number and
a plumbing team is sent to perform the initial investigation. If the cause is readily detected, such as
an obvious rupture in a pipeline, the team takes action immediately. If the cause is not obvious, the
team takes a chemical sample which is returned to the central laboratory for analysis. The basic
analyses of pH and conductivity are performed as well as a gas chromatography (GC) analysis for
the trihalomethanes (THMs) chloroform (CHCl3), dichlorobromomethane (CHCl2Br),
dibromochloromethane (CHClBr2) and bromoform (CHBr3). In general, a potable water source
provides strong trihalomethane peaks as shown in Figure 1, with very little background noise. In
addition, if the source of the leak is relatively close to where the sample was taken, the conductivity
of the sample should be close to that of the water supplied to the area.
Proceedings of the 2004 Water Institute of Southern Africa (WISA) Biennial Conference 2 –6 May 2004
ISBN: 1-920-01728-3 Cape Town, South Africa
Produced by: Document Transformation Technologies Organised by Event Dynamics

Figure 1. GC profile of a potable water leak.
Grey water or sullage also contains THMs but generally at a much reduced level owing to
combination and reaction with the organic matter in the water. There is also a general increase in
background noise. In addition, the conductivity of the water rises as a result of dissolved salts. An
example of a sullage water profile is presented in Figure 2.
Figure 2. GC profile of a sullage water leak.
Sewage waters, Figure 3, generally have very low or no THMs present but can usually be identified
by both their colour and odour. Ground waters, Figure 4, have no THMs, a variable pH and
generally only a slight odour. As can be seen from figures 3 and 4, it is often difficult to discriminate
between samples of sewage and ground waters purely on a GC spectrum. As a safeguard, all
samples which do not produce clear THM peaks are resampled. A sampling team from the
laboratory is sent to the site and takes bacteriological and chemical samples. As this sample is
only taken at least two days after the first sample, if the seepage is from a potable leak the flow will
generally have increased slightly. THMs should then be detectable as the surrounding organic
matter will have become saturated and no longer absorb the compounds being used for analysis.

METHOD
Figure 3. GC profile of a sewage water leak.
Figure 4. GC profile of a ground water leak.
The THMs are extracted from 50 mL of the seepage sample into 1 mL of pentane. The sample is
allowed to settle and 1 µL of the separated pentane is injected into the GC, a Varian 3600. The GC
is run using the electron capture detector (ECD).
The parameters for the run are as follows:-
Injection Volume: 1,0 µl Nitrogen gas is used
Injection Port A: 200 0 C Split ratio: 11
Detector B: 320 0 C Pressure: 8,0 psig
Column B flow rate: 1,6 mL / min Column: SPB-1 (30m x 0,25 µm)
Velocity: 28,8 cm / sec
Oven Program
70 0 C Isothermal for 5 minutes

Table 1. Ideal retention times for the various THMs under the above conditions.
Group ID Retention Time (min)
Pentane 1,88
CHCl3
CHBrCl2
2,02
2,34
CHBr2Cl 2,91
CHBr3
Data Retrieval and Analysis
A chromatogram is printed automatically after a run.
3,88
Sensitivity in µg / L with minimum detection limits in the order of 10 -1µ g / L.
DISCUSSION
As can be seen from the figures above, it is often difficult to distinguish the origin of seepage water
based solely on the THM profile. Figures 1 and 2 both had strong THM peaks, but when the
conductivity was examined it was seen that the sample for the potable leak was 27.8 mS/m, very
close to that of the mains supply while that of the sullage sample was 68.1 mS/m. In addition,
shaking the sample produced a light foam in the sullage sample and had no effect on the potable
sample. Increases in conductivity have however been noted in potable water samples where the
water has seeped through concrete or soil that has been treated with lime. Figures 3 and 4
represent the sewage and ground water samples. Here, the profiles are very similar. The
conductivities were 17.6 mS/m and 33.9 ms/m respectively, which would also not have been
sufficient evidence to make a decision as to source. When the E. coli results were examined, they
were >400 000 cfu/100mL and

taken to complete analyses and the additional costs involved have been found to outweigh the
benefits obtained when all samples are subjected to the full battery.
ACKNOWLEDGMENTS
I would like to acknowledge the plumbing and sampling teams who diligently take samples, often
under trying circumstances and the staff at the laboratory who analyse them with such skill.
Without these people Durban would literally be pouring money down the drain.