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DANDENONG SEWERAGE
AS THE WORK STEADILY
PROGRESSES.
That a water-borne system in the
disposal of sewage is undoubtedly
the best is admitted, and where,
possible is always adopted To de-
scribe the work which is being carried
on in Dandenong is not a task that is
at all uninteresting.
Pipes mad© of “various materials,,
such as earthernware,' concrete, or
cast iron of sufficiently large dia
meter, are used to carry the sewage,
and are laid underground at such
depths as will allow the sewage to
flow slowly from the highest point
to be served in the town to the treat
ment works, At the treatment works
the flow, is pumped up and aerated
until the effluent is approximately 99
per cent, pure water. ‘ f
Part of the preliminary work of in
stalling a sewerage system consists
of surveying the town - so that all
contour levies can be studied and the
whole town measured up. This is
done so that the minimum length of
pipe will be used, thus ensuring the
minimum cost.
In Dandenong the top soil, as it-is
• also in most places on the higher
levels', is dark in color, but of light
texture, and is from 12 to 18 inches
deep. This soil'when broken up melts
very quckly in water, and must
therefore be timbered up, where
shafts are sunk in it so as to conteract
the action of rain or surface drainage.
For three or four feet under the top
soil a hard dry clay confronts the
worker, but from that depth down to
about 16 feet a mixture of clay and
sand is encountered, . the clay pre
dominating, The mixture is easy to
work, and good progress can always
be made in it. At this depth at times
a good grade of pipe or potter’s clay
shows up, but so far in only small
quantities. In some places where a
depth of 20 feet has been attained a
very hard sandstone has delayed pro
gress. This stone is quite impervious
to the ordinary pick ano manual
labor, and had to be blasted out with
gelignite. It makes good paving for
footpaths when kept free from day.
On the lower levels of the town the
clay is of a short grained, greasy
type. It'is very hard to work, and
heavy to shovel, where trenches are
sunk in it they must be closely tim
bered so as to prevent the sides of
the trench sliding to the bottom. At
these levels a certain quantity of
underground water seeps into the
trenches; the flow of this water is
quite slow, and does not cause much
inconvenience to the workers exca
vating the ground and laying the
pipes. This ground water has a
high saline content, which is very in
jurious to cement, so earthenware
pipes, which are quite impervious' to
salt and other acids, are used in the
reticulation of Dandenong.
These pipes are laid on even grades
to ensure a steady flow of the sewage,
and where laid at a greater depth than
15 feet are cased in concrete to pre
vent the crushing of the pipes by the
weight of earth on top of them.
Where the ground water makes' the
bottom of the trenches wet and
sloppy the pipes are laid, on four
inches of crushed rock, but in all
other places sand is used as a bedding
for the pipes.
After each section of the pipes be
tween manholes is laid, it is tested
by water pressure for leakages at
joints, or from damaged pipes, which
must all be repaired or removed be
fore finally-filled in. The manholes
are built into the pipe lines' at every
junction, or change-of direction, and
are used for cleansing purposes or
for clearing stoppages which may
occur from time to time.
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