SEPTIC TANK
The
septic tank is the first step in the process, which is to separate the
solids from the influent stream. This is done by slowing the velocity
of the influent to allow greases and oils to float to the surface. This
also allows any solid matter to settle to the bottom. It is in here that
the anaerobic bacteria break down any organic materials. Greases and oil,
sheer volume of matter, introduction of toxins all play a part in hindering
the productivity of the bacteria, this accounts for the periodic need
for septic pumping. There are
two chambers in the septic tank with baffles in place to assist this process.
As the wastewater exits the septic tank it passes through a filter places
in the outlet baffle as an added pre caution against the passage of solid
matter. From here the wastewater is called effluent and goes to the pump
tank.
specified dose volume for your system. (I.e.;
90 gallons per dose) There is a pump at the base, along
with float controls, which are actuated by water level in the chamber. If
there is a malfunction and the effluent rises above the normal retention
volume the alarm will be actuated. There is enough capacity above the alarm
float for storage of one day's volume of effluent. Under normal conditions
the pump is actuated by a float control to pump a dose volume of effluent
to the sand filter. The effluent is pumped through a transport pipe into
a network of distribution pipes in the Top gravel layer of your sand filter.
The
sand filter is constructed as follows, starting from the Top down. Nine
inches washed gravel on the Top in which a network of distribution pipes
is installed. This network consists of 1 ¼ in. PVC laterals with
3/16 in. holes drilled at preset spacing to allow for equal distribution
of effluent in the sand filter. Under this gravel layer is twenty-four
inches of graded sand, which provides a medium for the aerobic bacteria
to further breakdown, and filters the effluent. And on the very bottom
is two layers of gravel in which is installed another network of collection
pipes.
These pipes collect the filtered effluent and transport it to a central
pump basin. This pump is installed, along with float controls, alarm etc.,
in much the same fashion as the pump tank. All of these layers are surrounded
on all sides except for the Top by a thirty mil PVC liner. This is done
to protect the ground water from being contaminated by effluent and vice
versa. From her the effluent is once again pumped via a transport pipe
to the drainfield.
This
is the standard type of dispersal system used in the majority of Onsite
Sewage Treatment systems. Drainfield trenches have a four inch perforated
pipe installed in gravel twelve inches deep. The trench width will vary
between twenty four and thirty six inches wide. The pipe is held six inches
up from the bottom of the trench and is covered with two inches of gravel.
Today the gravel is covered with filter fabric with older systems having
used biodegradable covering techniques. These trenches were installed level
following ground contours. On sloping sites more than one trench would be
used interconnected with solid overflow pipes. Each trench designed to fill
up before spilling over into the next trench below.
After
a septic tank is pumped there is a period lasting one to three months
where the full effectiveness diminishes. This is due to a loss of the
anaerobic community that had established itself in the tank. Make sure
that you really do need your tank pumped by checking your sludge and mat
depths prior to scheduling. Given low organic matter loading of a septic
tank, the pumping cycle could extend out ten years or more.