about your house

about your house
about your house
CE 34
Your S e p t i c S yst e m
Do you know where the water goes
when you empty a sink or flush a
toilet? If your home is in a city, the
wastewater likely goes into a municipal
sanitary sewer system to a sewage
treatment plant. If your home is
located in a rural area or a small
community, you are likely one of
the 25 per cent of Canadians whose
wastewater is treated by a septic system
(also referred to as an onsite wastewater
system). A septic system treats your
sewage right in your own yard and
releases the treated effluent back into
the groundwater (see Figure 1).
How Does My Septic
System Work?
A properly functioning septic
system receives all the wastewater
created from household use
(including toilets, showers, sinks,
dishwasher, washing machine, and
so on), treats the wastewater to a
safe level, and returns the treated
effluent to the groundwater system.
A conventional septic system is
composed of a septic tank and a soil
filter called a leaching bed. A leaching
bed may also be called a drain field,
an absorption field or a tile field.
Credit: Eric Brunet, Ontario Rural Wastewater Centre, University of Guelph
Figure 1
Wastewater recycling from an onsite system
Septic tank
The purpose of the septic tank is to
separate liquids from solids and to
provide some breakdown of organic
matter in the wastewater. A septic
tank is a buried, watertight container
made from concrete, polyethylene or
fiberglass. In the past, the tank was
sometimes made of steel or wood. If
you have a steel tank, it is likely
rusted through and needs replacing.
If you have a wooden one it is likely
rotting and may need replacing.
The size of the septic tank will
depend upon the size of the house
(number of bedrooms) and
household water use, with minimum
tank volumes ranging from 1,800 to
3,600 L depending on the province
or territory. Older tanks may be
smaller than those installed today
and tanks may have one or two
compartments, depending upon
when and where they were installed.
About Your House
Your Septic System
As wastewater from the house enters
the septic tank, its velocity slows
allowing heavier solids to settle to
the bottom and lighter materials to
float to the surface (see Figure 2).
The accumulation of settled solids
at the bottom of the tank is called
“sludge” while the accumulation of
lighter solids (greases and fats), which
form a mass on the surface, is called
“scum”. Anaerobic bacteria, which are
always present in wastewater, digest
some of the organic solids in the tank.
Clarified wastewater in the middle
of the tank flows by displacement
into the leaching bed for further
treatment in the soil layer.
Leaching bed
The partially treated wastewater
from the septic tank flows into the
leaching bed (see Figure 3). The
Credit: Eric Brunet, Ontario Rural Wastewater Centre, University of Guelph
Figure 2
Common septic tank with access risers and effluent filter
leaching bed is typically a network of
perforated plastic distribution pipes
laid in gravel trenches over a layer of
Credit: Eric Brunet, Ontario Rural Wastewater Centre, University of Guelph
Figure 3
Conventional septic system
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soil. In most provinces, the soil layer
must be a minimum of 0.7-1.2 m
above the high ground water table
or a restrictive layer such as bedrock
or clay and have a certain permeability
(absorptive capacity). Older systems
may have been constructed with clay
tiles instead of plastic pipes, while
new systems may use plastic chambers
to replace the gravel trenches and
perforated piping. The actual size,
design and layout of the leaching bed
is defined in provincial/territorial code
or regulation and is based upon the
volume of sewage generated, the
absorptive capacity of the underlying
soils, and the depth to the high
groundwater table or limiting/
restrictive layer. Wastewater can flow
by gravity from the septic tank to
the distribution lines, or where required,
can be collected in a pump chamber
and pumped to a leaching bed at a
higher elevation.
About Your House
Your Septic System
The leaching bed is a soil filter which
uses natural processes to treat the
wastewater from the septic tank.
Contaminants in the wastewater
include solid and dissolved organic
matter (carbon compounds), nutrients
(nitrogen and phosphorus) and harmful
bacteria and viruses. A slime layer of
bacteria, called a “biomat” layer, forms
at the bottom and sidewalls of each
distribution trench; and it is in this
layer where much of the treatment
occurs. Bacteria in the biomat layer
and surrounding soils consume the
organic matter in the wastewater as
well as transform ammonia nitrogen,
which is toxic to some aquatic
species, to the less toxic form of
nitrate-nitrogen. Harmful bacteria
and viruses present in the wastewater
are largely removed in the leaching
bed through filtration, predation
(eaten by other microbes) and
environmental exposure. Some
leaching bed soils will contain iron,
aluminium or calcium which can
adsorb phosphorus from the wastewater.
The soil bacteria which perform the
treatment require oxygen to function;
therefore the leaching bed must be
installed in soils that are not saturated
by surface water run-off or a high
groundwater table, and should
not be paved or covered over with
pavement, patios, sheds, and so on.
The leaching bed soil must be the
right type to retain the wastewater
long enough for treatment to occur,
while at the same time allowing the
wastewater to infiltrate into the
ground (refer to your provincial
or territorial regulations).
Credit: Eric Brunet, Ontario Rural Wastewater Centre, University of Guelph
Figure 4
Raised bed system
In cases where there is a sufficient
separation from either the high
groundwater table or bedrock, the
network of drainage piping is installed
directly in the native soil or in imported
sand if the permeability of the native
soil is not suitable. This is called a
conventional system (see Figure 3).
In cases where the high groundwater
table or bedrock is close to the surface,
the leaching bed must be raised so
that there is sufficient unsaturated
soil under the drainage piping. This
is called a raised (bed) system or a
mound system (see Figure 4).
Aerobic treatment technologies
There are many site conditions where
it is impractical to impossible to install
a conventional septic system such
as: high groundwater table, bedrock,
poor soil conditions (i.e. clay, silt, till) or
inability to meet the setback distances
from surface water, wells or property
boundary lines. In these cases, an
aerobic treatment technology is often
used. These treatment technologies
are proven technologies which have
been on the market since the 1970s
with numerous installations across
North America. Aerobic technologies
treat the wastewater to a higher level
(secondary and tertiary) than a septic
tank, permitting the treated effluent
to be discharged into a much smaller
area than is required for treatment
by a conventional leaching bed. Each
province and territory has its own
regulations for aerobic treatment
technologies and you should consult
with your local regulatory authority
to determine which technologies are
approved in your locality.
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About Your House
Your Septic System
Credit: Eric Brunet, Ontario Rural Wastewater Centre, University of Guelph
Figure 5
Is the technology or product
brand approved in your
Does the manufacturer provide a
reliable service contract and support
in your area?
What are the maintenance
requirements and costs associated
with the technology (frequency
and timing required for inspections,
effluent sampling, and replacement
What is the cost and availability
of replacement parts?
What are the annual energy costs
(pumps, aerators)?
What are the frequency, volume
and costs of pumping out
the system?
What are the special considerations
for installing the system for
seasonal use and winterization?
Alternative treatment technology
Aerobic treatment technologies
typically have three components: a
settling tank (this may be smaller than
a conventional septic tank), the aerobic
treatment unit which removes much
of organic matter from the wastewater,
and a dispersal system, which is often
a small leaching bed (see Figure 5).
Aerobic treatment technologies all
rely on aerobic micro-organisms to
break down the organic matter in
the wastewater. In order to optimize
treatment, the treatment unit vessels
either include a material to support
the growth of micro-organisms
(called attached growth media),
or a continuous mixer to keep
micro-organisms in suspension
(called suspended growth). Many
technologies utilize either an air
pump or blower to provide oxygen
to the micro-organisms, while some
technologies are designed as “trickling
filters”, where effluent is dosed onto
an unsaturated media and the
micro-organisms use the oxygen in
the air which surrounds the media.
The treated effluent is typically
discharged into a small leaching
bed, although there are alternative
methods in some jurisdictions
including pressure distribution systems
near the soil surface or even discharge
to surface waters. Consult with your
provincial/territorial authority to see
which methods of dispersal are
permitted in your area.
In most provinces, homeowners
with aerobic treatment technologies
are required to have a maintenance
contract with an authorized service
provider to inspect and maintain
their systems. Things to consider
when purchasing an aerobic treatment
technology are :
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What Do I Need to
Do to Keep My Septic
System Working?
Access risers
Having easy access to the septic
tank is the first step to routine
maintenance. For tanks that are
buried in the ground it is a very
good idea to install access risers,
which extend the tank lids to or
near the surface (see Figure 2).
Should there be a need to access the
tank during the winter, risers will
make the job much easier. Risers
can be made of plastic or concrete
and must be secured against entry.
About Your House
Your Septic System
Tank pump-out
Over time, the sludge will build up
in the bottom of the septic tank. If
the sludge is allowed to accumulate
it will eventually flow into the leaching
bed and rapidly clog the distribution
pipes. Once the pipes become clogged,
the wastewater will either seep to the
surface of the ground, or worse yet,
back up into your house. Not only can
a clogged septic system be hazardous to
the environment and to your family’s
health, it also represents a very
expensive repair bill.
A septic tank should generally be
pumped out every three to five years
or when 1/3 of the tank volume is
filled with solids (measured by a
qualified practitioner). The frequency
of pumping out the tank will depend
upon household water use (number
of people) and the size of the septic
tank. For example, a family of five
with a 2,300 L tank may require a
tank pump-out as frequently as
every two to three years, while a
retired couple with a 3,600 L tank
only require a tank pump-out
every five to seven years. Some
jurisdictions define how frequently a
septic tank must be pumped out.
In the province of Quebec, for
instance, septic tanks are required to
be pumped every two years for full
time residences and every four years
for seasonal residences.
The best time to have the tank
pumped out is summer to early fall.
At these times, the ground will not
be frozen, allowing easier access to
the tank, and the biological activity
in the tank can re-establish itself
What not to put down the drain
before it gets too cold (microorganisms like it warm). In the
spring, a high water table caused by
melted snow can sometimes create
sufficient pressure on the underside
of an empty tank to push it up out
of the ground. This is more of a
concern with lighter tanks made of
polyethylene or fibreglass than those
made of concrete.
Never inspect or pump out a
septic tank yourself. There is no
oxygen in the tank for you to
breathe and the tank contains
deadly gases which can kill you in
only a few seconds. When it is
time to clean or inspect your
tank, call a licensed pumper.
Effluent filters
An effluent filter is a relatively new
accessory for a septic tank. It is a simple
filter which is installed at the outlet
of the septic tank to prevent large
solid particles from flowing out of
the septic tank and into the leaching
bed. An effluent filter could prevent
the premature clogging of your leaching
bed with solids. There are many
different effluent filters on the market,
so consult with a local contractor to
determine which filter is best for
your system.
Effluent filters need to be cleaned
periodically depending upon the
type and size of filter and household
water use. Some filter models can be
fitted with an alarm which sounds
when the filter requires cleaning.
Because septic systems rely on bacteria
to break down the waste material, it
is important that you don’t poison
these micro-organisms. Even small
amounts of paints, solvents, thinners,
nail polish remover and other common
household compounds flushed or
poured down the drain can kill the
bacteria that break down the organic
matter in the wastewater. Household
disinfectants such as laundry bleach
or toilet bowl cleaner can be used in
moderation without affecting the
operation of the septic system; however,
overuse of disinfectants can kill the
bacteria in a septic tank. Some
manufacturers promote the use of
septic tank “cleaners”, “starters” or
“enhancers” to aid in the digestion
of the waste. These products are
typically of little value and are not
You should avoid putting anything
into the septic system that doesn’t
break down naturally or anything
that takes a long time to break down.
Materials such as oils, grease, and
fat, disposable diapers, tampons and
their holders, condoms, paper towels,
facial tissues, cat box litter, plastics,
cigarette filters, coffee grounds, egg
shells, and other kitchen wastes,
should never be put into the septic
system. You should also avoid the
use of in-sink garbage disposal units
(“garburators”) unless the septic
tank and leaching bed are designed
to accommodate the increase water
and organic load created from these
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About Your House
Your Septic System
Do I Need to
Control My
Water Usage?
Every time you put water into the
septic tank, that same amount of
water moves into the leaching bed.
The longer the wastewater is retained
in the septic tank, the more the effluent
has less suspended solids and organic
matter. Conversely, if the water moves
too quickly through the septic system
(through excessive water use in the
household), the solids may not have
time to settle out and then could
flow into the leaching bed. Therefore,
whenever possible, you should try to
regulate the amount of water entering
the septic system; for instance, laundry
can be spread out over several days
during the week. You can reduce
water usage by installing water saving
features in plumbing fixtures and by
only running the washer or dishwasher
when it is full. Fix leaky faucets and
watch out for running toilets—a
running toilet can waste a huge amount
of water and can wash out a septic
tank. Foundation drainage (sump
pump) and furnace condensate should
be excluded from the septic tank. You
can also control the amount and
timing of wastewater you put into
the system by using a discharge pump
package to dose the leaching bed.
How Do I Look After
the Leaching Bed?
Looking after the leaching bed is
easy. There’s nothing you have to
do, but there are a few things you
shouldn’t do. The area over the
leaching bed should have a good
cover of grass. Good ventilation and
adequate sunlight should also be
maintained to promote evaporation.
This means that nothing should be
constructed over the leaching bed
including: parking areas, patios,
tennis courts, decks or storage sheds.
Covering the leaching bed will
prevent oxygen from getting into the
soil. The bacteria responsible for
digesting the wastewater need
oxygen to survive and function.
You should not drive vehicles or
machinery over the bed, as the
weight could crush the distribution
pipes or compact the soil. In winter,
you should also keep snowmobiles
off the leaching bed. The compaction
of the snow will reduce its natural
insulating effect, increasing the
chances of the pipes freezing.
Don’t plant trees or shrubs near the
leaching bed. The roots of some trees,
especially willows and poplars, will
travel significant distances to reach
water. The roots can plug and damage
the distribution pipes. Lastly, don’t
water the grass over the leaching
bed and ensure that all surface
drainage (particularly eave troughs)
is directed away from the leaching
bed. The additional water may
interfere with the ability of the soil
to absorb and treat the wastewater.
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The leaching bed of a conventional
septic system should last at least
20 years; however, the distribution
lines will eventually become clogged
with biomat and the bed will have
to be repaired or replaced.
How Will I Know if I
Have a Problem with
My Septic System?
Some of the warning signs that your
septic system may be failing include
the following:
The ground around the septic
tank or over the leaching bed may
be soggy or spongy to walk on.
Toilets, showers and sinks may
back up or may take longer than
usual to drain.
Occasional sewage odours may
become noticeable, particularly
after a rainfall.
Gray or black liquids may be
surfacing in your yard or backing
up through fixtures into the house.
E. coli or fecal coliform indicator
bacteria may be found in nearby
well water or in a surface ditch
close to the leaching bed.
The water level in the septic tank
is higher than the outlet pipe
(this indicates that the water is
ponding in the distribution lines)
—inspection should be conducted
by a qualified practitioner.
Wastewater is ponding in the
distribution lines—inspection
should be conducted by a qualified
practitioner or an engineer.
About Your House
Your Septic System
How do I Prevent my
System from Freezing?
Septic systems are most likely to
freeze in periods of cold temperature
when there is little snow cover. The
first line of defence against system
freezing is adequate insulation. Adding
0.3 m (1 ft) of mulch (leaves, straw,
hay) or letting the grass grow long
over the system in the fall will provide
a good insulating layer. Snow can
also be piled over the system in the
early winter. Other options include:
insulate the pipe from the house to
the septic tank, add Styrofoam sheets
above the septic tank, and increase
the soil cover over the system.
There are three major causes of
system freezing :
1— Pipes not draining properly
Any standing water in pipes may
freeze. This may result from poor
installation without sufficient slope
or ground settling or frost heaving
over time. The solution to this
problem is to excavate and replace
the faulty section of piping.
2— Low water usage
Water slowly trickling through
piping (for instance from a leaking
tap or toilet) can create a film of
water which can freeze the line
solid. Low water use (or vacancy)
for an extended period of time can
lead to the septic tank freezing. If
you are going away for an extended
period of time during the winter, it
is a good idea to have the tank
pumped out before you leave.
3— Waterlogged system
line, replacing the septic tank to
ultimately replacing the entire
leaching bed.
If your leaching bed is saturated
(either through poor design or
clogging of the distribution lines)
it could freeze solid. If this happens,
the only solution is to use the septic
tank as a holding tank until spring,
when the leaching bed thaws and
can be repaired or replaced. This
means the septic tank will have to
be pumped out every time it fills
up, which could be as frequently
as twice a week. If you have to use
your septic tank as a holding tank,
it would be a good idea to have the
pumper install a high level alarm in
the tank to indicate when pumping
is required.
Your Septic System
and the Law
If your system freezes call a qualified
practitioner (pumper or installer).
Many contractors have high pressure
steamers to defrost frozen piping or
can install heat tape or a tank heater.
Do not add antifreeze, salt or additives
to the tank and do not try and run
water continuously to unfreeze
the system.
What If I Have to
Repair My Septic
If you notice a problem with your
system, it is important that you
take action immediately to protect
your health and the environment.
Contact a qualified practitioner
to advise you on how to proceed.
Repairs can range from pumping
out the septic tank, repairing a
broken tank baffle or cracked pipe,
levelling the distribution header
You are required by law to report
any problem to your local authorities
before proceeding with repairs or
replacement. A final inspection will
need to be carried out and a Use
Permit granted before you can legally
use a new or altered septic system.
Your contractor and/or your local
authorities can also help you determine
the required size of your septic system.
You may find that you need a larger
system than you currently have. If
you are repairing, replacing or installing
a new septic system, you will also have
to be aware of the legal limitations
imposed on where your septic system
can be located with respect to your
house and your well, your neighbour’s
house and well, and nearby bodies
of water. These distances are required
to help ensure that wastewater from
your septic system cannot reach and
contaminate nearby water supplies.
Depending upon the province, the
leaching bed must be at least 1.5-9 m
from a property line, 3-11 m from a
building, 15-30.5 m from a well, and
15-75 m from a body of water.
The agency responsible for onsite
septic system permits varies depending
on the province or territory and is
described in Table 1.
Canada Mortgage and Housing Corporation
About Your House
Your Septic System
Table 1
Provincial/territorial septic system regulations
Prince Edward Island
Department of Technology and Environment
Environmental Protection Act—Sewage
Disposal Regulation
Newfoundland and Labrador Department of Health
Public Health Act—Sanitation Regulation
Nova Scotia
Department of the Environment
Environment Act—On-site Sewage
Disposal Regulation
New Brunswick
Department of Health and Community Services
Health Act—Regulation 88-200
Department of Environment
Environmental Quality Act—Regulation
Respecting Wastewater Disposal Systems
for Isolated Dwellings
Ministry of Municipal Affairs and Housing
Ontario Building Code Part 8
Department of the Environment
Environment Act—Private Sewage
Disposal Systems and Privies Regulation
Department of Health
Public Health Act—Plumbing and Drainage
Ministry of Labour
Safety Codes Act—Alberta Private Sewage
Systems Standards of Practice
British Columbia
Ministry of Health Services
Health Act—Sewerage System Regulation
Northwest Territories
Department of Health and Social Services
Public Health Act—General Sanitation
Yukon Territory
Department of Health
Public Health and Safety Act—
Sewage Disposal System Regulations
Canada Mortgage and Housing Corporation
About Your House
Your Septic System
Local municipal offices or public
health offices
Licensed septic system installers
(check the Yellow Pages™)
Provincial and territorial
ministries responsible for septic
systems (e.g. environment,
Canada Mortgage and Housing
Corporation (May 2008)
USEPA Septic (Onsite) Systems
Homepage (May 2008)
Ontario Rural Wastewater Centre
(May 2008)
National Environmental Services
Center (May 2008)
Centre for Water Resources Studies
(May 2008)
Canada Mortgage and Housing Corporation
About Your House
Your Septic System
To find more About Your House fact sheets plus a wide variety of
information products, visit our website at www.cmhc.ca.You can also
reach us by telephone at 1-800-668-2642 or by fax at 1-800-245-9274.
Priced Publications
Household Guide to Water Efficiency
Order No. 61924
Free Publications
About Your House fact sheets
Buying a Toilet
Hiring a Contractor
Buying a House With a Well and Septic System
Order No. 62935
Order No. 62277
Order No. 63319
©2001, Canada Mortgage and Housing Corporation
Printed in Canada
Produced by CMHC
Revised 2002, 2003, 2005, 2008
Although this information product reflects housing experts’ current knowledge, it is provided for general information purposes only.
Any reliance or action taken based on the information, materials and techniques described are the responsibility of the user. Readers
are advised to consult appropriate professional resources to determine what is safe and suitable in their particular case. Canada Mortgage and
Housing Corporation assumes no responsibility for any consequence arising from use of the information, materials and techniques described.
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