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1. What is a septic tank?
2. What is a conventional septic system?
3. What is a leaching bed?
4. How does a conventional septic system work?
5. What treatment occurs in the septic tank?
6. What treatment occurs in the leaching bed?
7. Can I do anything to improve treatment in
my system?
8. What type of maintenance should I perform
on my system?
Q1. What
is a septic tank?
A septic tank is a water-tight container, frequently made
of concrete, that's buried somewhere in your yard and accepts
all sewage from your house. "Sewage" includes not
only the toilet wastes but shower, sink, kitchen, and washing
machine wastewater as well. The tank has no moving parts and
is just the first part of your onsite wastewater system. In
Ontario the septic tank must have at least two chambers or
compartments. The first chamber must be larger than the second
chamber. Outlets must be fitted with baffles to prevent scum
from going to the leaching bed. Access manholes should be
accessible for maintenance purposes.
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Q2: What is a conventional
septic system?
A conventional septic system consists of a septic tank and
a leaching bed consisting of gravel filled trenches constructed
in the native soils. This is the most common type of system
installed in Ontario.
tank is buried, but the access manholes or risers should be
accessible for maintenance purposes
in Ontario there must be at least two chambers in the septic
tank (facilitate solids settling)
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Q3. What is a leaching bed?
A leaching bed consists of a number of individual
absorption trenches laid parallel to one another. Each trench
consists of a perforated PVC pipe (3 or 4 inch diameter) surrounded
by clean gravel. Filter cloth is laid on the top of the gravel
to prevent fine particles in the backfill from clogging the
spaces between the gravel. Each trench, or lateral, is connected
to a header pipe and is sloped away from the header at 0.5%.
Wastewater from the septic tank flows to the header, which
evenly distributes the effluent to the laterals. Effluent
flows down the perforated pipe and percolates through the
gravel into the underlying soil where the bulk of treatment
occurs.
Depending on the relative elevations of the septic tank and
the leaching bed, a pump may be required to lift effluent
from the tank to the header of the leaching bed.
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Q4: How does a conventional
septic system work?
Generally, wastewater generated in the house is transported
to the septic tank via the building sewer. Wastewater stays
in the septic tank for approximately two days, and during
this time the solids settle out and oil and scum float to
the top. Only the remaining liquid moves out to the leaching
bed. In the leaching bed, the liquid is dispersed into the
native soils where it is treated by a variety of chemical,
physical and biological means and eventually returned to the
groundwater. It is very important that solids are retained
in the septic tank and not conveyed to the leaching bed, as
they can quickly clog a trench and cause failure of the bed.
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Q5: What treatment occurs in
the septic tank?
The septic tank provides primary treatment of the
wastewater from the building. The first compartment of the
septic tank is for separating the solid and floatable material
from the liquid portion of the wastewater. Wastewater flows
from the building into the first compartment of the tank,
where it is retained for approximately 1.5 days. During that
time, solids settle out and sink to the bottom, and oils and
greases separate and form a scum layer along the top of the
liquid. A relatively clear layer of liquid is created between
the scum and solids layers. The remaining clear liquid flows
through holes in the middle of the baffle wall into the second
chamber of the tank, from where it goes out to the leaching
bed. When wastewater flows into the tank, equal volume of
effluent is transferred out of the tank and to the leaching
bed.
Bacteria present in the wastewater breaks down, or "eats
up" solids that have settled to the bottom of the tank.
In a septic tank, these bacteria are called anaerobic bacteria
because they survive best in low oxygen environments. As long
as these bacteria are provided with time and warm temperatures,
they can break down some of the solid material in a septic
tank. However, the septic tank only accounts for approximately
10 - 20% of the treatment in a conventional system.
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6. What treatment occurs in
the leaching bed?
Treatment in the leaching bed occurs through a variety of
physical, biological and chemical means. Effluent from the
second chamber of the septic tank flows to the leaching bed
header and is distributed equally to the laterals. Wastewater
then moves from the perforated pipe into the gravel in the
absorption trench, and eventually into the underlying soil.
As this happens, some solids are filtered out (this occurs
as the wastewater percolates all the way down the soil column).
This is the physical part of the treatment in the leaching
bed.
At the soil/gravel interface, a biomat forms that contains
many bacteria. These bacteria are aerobic bacteria, meaning
they thrive in the presence of oxygen. Similar to the bacteria
in the septic tank, they break down, or eat microscopic solids
in the wastewater, but because they are aerobic bacteria,
they work much faster. Soil microorganisms also feed and break
down wastewater. This is the biological component of the treatment
in the leaching bed.
Chemical reactions between certain soil components and nutrients
in the wastewater also occur. An example of the is the cation
exchange which binds phosphorous to some soil particles.
All together the leaching bed is responsible for 80 - 90%
of the treatment in a conventional onsite system. It should
be noted that treatment will not occur in saturated soils
(full of water, from high or perched water table).
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Q7. Can I do anything to improve
treatment in my system?
In order to fully maximize the treatment of your
onsite system, you should only flush biodegradable material
down the drains. Caustic or acid fluids, or bleaches, will
kill the bacteria in your system, effectively halting treatment.
Also avoid flushing things like paint, paint thinners etc.
The use of an effluent filter is a relatively inexpensive
way to prevent solids from moving from your tank into your
leaching bed. Frequently mowing the lawn on your leaching
bed will improve evapotranspiration and airflow into the leaching
bed, improving treatment in the bed as well.
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Q8. What type of maintenance
do I have to perform on my system?
Periodically the tank must be pumped to remove the
solids that have accumulated in the tank. According to the
OBC, this must be done when the working capacity of the tank
is less than 2/3 of its original depth. Generally, the industry
recommends that a single family residence pump out their tank
every 3 - 5 years.
In addition to pumping out the tank, you should periodically
make sure that the baffles on the inlet and outlet of the
tank are in place and functioning as intended. If you have
a pump chamber, check to make sure the pump is working and
the alarms are functional. The leaching bed should be periodically
inspected for soft spots, break out or other defections such
as excessive erosion on the side slopes.
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