Planning (Practical Exercise)
Session Objectives
· To provide a
practical example of the process of planning water supply monitoring programmes
which cover a wide range of conditions.
· To reinforce the need to
develop monitoring programmes which are linked to decision-making and management
needs.
Outline
1. Divide the participants into at least two groups.
2. Provide the participants with the attached description and
ask one or more groups to design a health-based drinking-water quality
surveillance programme for the town and the remaining groups to design a quality
control monitoring programme for a water supplier.
3. Ask the groups to make a presentation on the programmes
designed and discuss these in plenary.
NB: This practical is best run over several days. Therefore, the
groups should be given the background information at the start of the workshop
and asked to present their findings on the last day.
Monitoring Programme Design
The town of Terebaka serves a total population of 105,000. The
town is a regional centre of importance and has a busy market selling foodstuffs
and a variety of hardware and clothes and an industrial area. The town is the
centre for the surrounding district and the population is significantly
increased on market days. The town is also an important rail and bus terminus
and the short-term transient population is high.
The town has a centralised piped water supply which serves 85
per cent of the population with a mixture of in-house and yard level water
supply service (roughly a 40-60 split). In addition, a number of public
tapstands are located in the market and at the bus and rail stations. The piped
water supply utilises two main sources: a reservoir situated 20 kilometres to
the north of the town and connected to the water treatment plant; and a well
field (series of boreholes) 10 kilometres to the west of the town which joins
the distribution system at the major storage tank on the western extremity of
the town.
The treatment plant utilises coagulation-flocculation-settling
through two conventional settlers set in parallel. This is followed by rapid
sand filtration and the plant has two filters per settler. The water is
disinfected with hypochlorite does through a pulse doser into the final clear
well. The water is then pumped to the main town storage tank which feeds the
distribution systems which passes through 6 subsidiary tanks spread around the
city.
The well field water is pumped to a central collector tank where
it is chlorinated using a gas chlorinator and the water is then pumped to the
major tank on the west of the city, form where the water is distributed through
the main system.
The treatment plant has suffered a number of failures during the
recent past and the coagulation-flocculation-settling in particular is known to
be inefficient. Problems have arisen through the lack of coagulant and
insufficient settling time. Some problems have also been encountered with the
chlorination of water form both sources.
The distribution system is old and has a leakage rate of around
3- per cent. Several "hotspots" of pipe leakage are known and there are also
several areas of known low pressure within the system.
The parts of the town not served by the main pipe system are on
the periphery of the town and utilise hand-dug wells in most areas, although
several private boreholes have been sunk.
Design a monitoring scheme for Terebaka, indicating the range of
analysis, frequency of sampling, type of sampling points, location of sampling
points and frequency of sanitary inspection. Indicate the objectives of your
monitoring programme and highlight the actions you would take on the basis of
the results received.
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Figure
