SEWERAGE
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metal scrap, such material
won't cave in over time. Atop
this medium, in the centre of
the trench, is laid 50 to
63mm rigid drain pipe, cut
half through with slots on the
underside every 10cm or so,
taking into consideration the
necessary fall of 1:40 over the
entire length. If the trenches
are herringboned proper joins
are installed and the ends are
blanked off with blanking
pieces.
Over the entire length and
width of the pipe geo-fabric
(Bidem) or shade cloth is laid,
which will not rot, and which
prevents soil particles and
sand from filtering into the
hard matter (and preventing
roots from growing into the
trenches), while still allowing
rainwater to filter downwards.
Another method is to lay the
shadecloth under the pipe
and to bed the pipe in river
sand before filling the
remainder of the trench with
Side-view of a herringbone trench soakaway
soil. This is an unnecessary
additional cost, however, and
still allows roots to penetrate
to the pipe where they block
the slots.
The trench is then back-filled
with soil to surface level and
planted with grass. The
the liquid which finally enters
the soil.
The gaps provide for the
liquid and air to flow. The
micro-organisms are aerobic,
ie they need air (oxygen) to
live (unlike the microorganisms in the septic tank
itself, which are anaerobic).
After passing in contact with
the media and their attendant
organisms the liquid then
seeps from the trench out into
the soil. Here it is filtered and
receives further treatment by
the soil bacteria and plants. It
is, however, still not "pure" or
harmless.
Pollution of ground water by
septic systems is of particular
concern in smallholding areas
where septic systems and
boreholes are found in
relative profusion. Siting of
boreholes and septic systems
is crucial in ensuring that
borehole water remains clean
and, while you may be able
to ensure that your septic
system is built far away from
your borehole on your own
plot, can you be sure that
your neighbour's system is not
close to your borehole?
For this reason, if your
borehole water is used for
animal or human drinking it
should be subjected to regular
testing for pathogens and
harmful chemicals.
beauty of this system is that it
is extendable: should the slots
in any section of the pipe
become blocked the fluid will
simply flow further down the
pipe. Furthermore, should the
entire system become
clogged, one of the blanking
pieces at the end of the pipe
is simply cut off and further
extensions dug and laid.
What is put into the trench as
filler is important. Old tyres
are not good, neither are old
clay bricks (they disintegrate
in time). The media in the
trench not only prevents it
from collapsing but also
provides surface area on
which microorganisms attach
themselves. The larger the
surface area, the more
accommodation for microorganisms, and the cleaner
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