Frequently
Asked Questions
Find
Here: A good
explanation
of what septic
systems are,
how they
work, and why they fail, contributed
by Lockwood, Dietershagen Associates
Licensed Professional Engineers, Clifton
Park, NY.
Contents:
Frequently
Asked Questions
- Septic
FAQ's
What
are Septic Systems?
by Lockwood, Dietershagen
Associates Septic systems
are considered
to be on-site systems designed
to safely
dispose of biological sanitary
waste. "Gray
water", such as laundry
waste, is part of the waste
system, but it
may not result in what is
referred to as "biological" waste.
We will address "gray
water" waste
as it impacts the design
of a septic system.
How
do Septic Systems
Work?
Basically a septic system
provides a "holding Tank" where
natural bacterial action decomposes
human
waste products into environmentally
acceptable components - the
major end-components being water,
mixed
with some other components that
are not readily consumed by
the bacterial
action, gases, and undigested
solids. The end products, except
the undigested
solids, are then discharged
to the on-site environment.
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What are the Components
of a Private
Septic System?
The things that
are most obvious
are the things
seen every day
- the sinks, toilets,
and pipes in a
normal house.
What are not visible
are the things
that are underground;
the things that
are underground,
and the ground
itself, greatly
impact how a septic
system works.
The individual
parts of the system
are the septic
tank, a distribution
box, and a leach
field. Bacterial
action takes place
in the septic
tank where the
end products are
mainly water,
gases, and undigested
material, called
sludge that sinks
to the bottom
of the tank and
scum that floats
to the top of
the tank. The
septic tank contains
baffles that prevent
any scum that
floats to the
surface and sludge
that settles to
the bottom from
passing out of
the tank. The
gases that are
generated vent
to the atmosphere
via the plumbing
vent system. From
the septic tank,
the segregated
and relatively
clear liquid flows
into a small distribution
box where it is
then metered out
to several perforated
pipes. These perforated
pipes then deliver
the liquid to
a large soil surface
area, called a
leach field, or
absorption field,
for absorption.
The soil also
acts as a filter
to remove any
small amounts
of solids that
may be carried
along with the
liquid. The sludge
in the bottom
of the tank must
be periodically
pumped out and
properly disposed
of.
There are other
kinds of systems
for special situations,
but the septic
tank and leach
field is the most
widely used system
in our area. The
following discussion
concentrates on
this type of system.
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Where are
These Components
Located?
The concrete,
or sometimes
steel, septic
tank is
buried in
the ground,
usually
a minimum
of 10 feet
from the
house. The
top of the
tank is
usually about
one foot below
the soil surface
so it can
be periodically
opened for
inspection
and pumping.
If you do
not know
for sure where
the tank is
located, the
first step
is to locate
where
the house
sewer pipe
leaves the
house. In
a house
with a basement,
this is where
the pipe passes
through the
wall. Locating
the exit
point may
be more difficult
for
a house with
no basement.
If the
pipe exit
can be found,
the
tank normally
begins about
10 feet from
the
house outside
wall and in
line with
the house
sewer pipe.
If the soil
is not
frozen, you
can usually
find the
tank by pushing
a slender
metal rod
into the ground
until it hits
the buried
tank.
You can buy
a metal rod
about
1/8 inch in
diameter for
a few dollars
at most hardware
stores. Be
careful
when probing
for the tank
and avoid
hammering
the metal
rod into
the ground
- you could
break a
sewer pipe.
The distribution
box is much
smaller than
the septic
tank and is
usual
found about
20 feet from
the
house. It
too is usually
only
about one
foot below
the ground.
Again, you
can
probe the
soil carefully
to locate
the distribution
box with a
slender metal
rod.
From the distribution
box, several
pipes direct
liquid
to a series
of pipes in
trenches
called laterals.
The pipes
in the trenches
have
holes in them
to allow the
liquid to
be evenly
distributed
within the
trench.
To keep the
pipes from
being blocked
with soil
and
to provide
a space for
water to be
stored while
it
is being absorbed
by the soil,
the pipes
are laid
in a bed of
crushed stone.
Above the
stone is a
soil filter
(usually
one or two
layers of
what is called
untreated
building
paper). Above
the soil filter
is top soil
in which grass
is
planted.
Equally important
is WHERE THE
COMPONENTS
SHOULD NOT
BE. If there
are wells,
either yours
or
a neighbor's,
the leach
field must
be a minimum
of 100 feet
from
the location
of the well.
In some
areas, the
well is not
allowed
to be down-slope
from the leach
field. If
there is a
stream or
pond, the
leach field
must also
be a minimum
of 100 feet
from
the mean high
water mark.
Normally,
no part of
the
system should
be within
10 feet of
a property
line. In some
areas and
in unusual
conditions,
minimum
distances
may be greater
than
those noted
here. In addition,
no
part of the
system should
be under
a porch or
driveway and
you should
not drive
heavy
vehicles (including
automobiles)
over the system
lest
the system
be damaged.
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Care
and Maintenance
Conventional
septic
systems
are
not entirely
care
free.
The
undigested
solids
(sludge)
in the
bottom
of the
septic
tank
should
be pumped
out
every
two to
four
years,
depending
on usage
and
tank
size.
If the
sludge
is not
removed
periodically,
it will
eventually
carry
over
into the
leach
field
and
cause
the field
to fail.
A well
designed
system
can handle
a reasonable
amount
of normal
household
chemicals
such
as drain
cleaners,
laundry
detergent
and bleach;
excessive
usage
can
be detrimental.
You should
avoid
putting
in chemicals
that are
toxic
to the
bacteria,
such as
paint
thinner,
solvents,
insecticides,
etc. Cooking
fats
and grease
should
also
be avoided.
If a garbage
disposal
is used,
more frequent
tank
pumping
may be
needed.
Depending
on the
size of
the tank
and your
location,
plan on
a
cost
of about
$200 each
time
the tank
is pumped.
When the
tank
is pumped,
your service
person
should
also check
the
tank baffles
for possible
damage;
ask them
to do
this inspection
before
you
contract
with them.
While
the tank
is open,
the service
technician
can also
run
some
water
from a
hose into
the distribution
box to
get
an
indication
that the
leach
field
is also
still
functioning;
ask if
the
company
offers
this service.
Estimated
Septic
Tank Pumping
Frequency
In Years
(assumes
no garbage
disposal)
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Why
Septic
Systems
Fail
If
the liquid
effluent cannot
soak into the soil
surrounding the leach
field, sewage
may back up into
the system and overflow
into the house
or puddle on the
surface of the
ground. There
are several
possible causes
for this problem.
1.
Poor Soil Conditions;
Faulty Design
or Installation
A
leaching system
placed in unsuitable
soil, a system
that is too small
for the house
it serves, or an
improperly constructed
system may lead
to early failure.
2.
Soil Clogging
If
sludge or scum
is allowed to
escape into the
distribution box and
from there
into the leach
field, the
soil will quickly
become clogged.
If this happens,
the liquid
will no longer
soak, or percolate,
into the soil.
This condition can be
caused by broken
baffles in the
septic tank that
allow sludge
or scum to
escape. Failure
to have the tank
pumped can also
lead to a
situation where
the sludge and scum
overwhelm the baffles.
3.
High Water
Table
During
wet, or
abnormally wet,
seasons groundwater
may rise
into the
leach field
and force
sewage upward
to the
ground surface.
This condition
may mean
the system
has to
be re-installed
at a
higher level.
It may
also be
possible to
intercept the
high groundwater
with a
series of
drains around
the system
called "curtain
drains".
4.
Roots
The
roots of trees
and bushes planted
too close to the
system can
sometimes enter
and block the pipes
of the system.
Removal of the
plants and clearing
the pipes of the
roots is usually
required.
5.
Physical Damage
Trucks
or heavy
equipment
passing
over the
system can
damage
pipes and
joints to
the
point of rendering
the system
inoperable.
You should
be aware
of the location
of the system
and direct
traffic
to avoid such
damage.
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How
Long
Should
a Septic
System
Last?
You
can
expect
a conventional
septic
system,
such
as
that
being
described
here,
to last
about
30 years.
Some
systems
last
much
longer
and
some
systems
can
fail
earlier
for
reasons
like
those
noted
above.
Other
things
can
also
affect
the
life
of
a septic
system.
For
example,
a
system
may
have
been
providing
satisfactory
service
for
a previous
owner
for
many
years,
only
to fail
shortly
after
you
have
bought
the
house.
If
the
previous
owners
were
a
working
couple
with
no children,
the
system
was
probably
not
heavily
used;
if
yours
is
a family
of
six,
the
added
load
could
push
a marginal
system
over
the
edge
and
into
failure.
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What
are the
Signs
of a
Failing
System?
Sewage
backup
into
the
home
is
one
possible
sign
of
a
failing
system.
However,
backup
can
also
be
simply
the
result
of
a
blockage
somewhere
between
the
house
and
the
septic
tank
(this
is
relatively
easy
to
fix).
Another
possible
sign
of
failure
is
a
smell
of
sewage
outside
the
house.
If
this
smell
is
more
noticeable
after
a
lot
of
water
has
been
put
into
the
system
-
multiple
showers
or
several
loads
of
laundry
(if
the
laundry
waste
discharges
into
the
septic
system),
for
example
-
this
may
be
an
indication
that
the
leach
field
is
failing.
The
smell
may
also
be
accompanied
by
a "spongy" feeling
in some areas
of the leach field,
near the distribution
box, or near the
septic tank. The "spongy" feel
may be caused
by water and waste
being pushed to
or near ground
level. If ponding
water is also
seen, this is
called "breakthrough" and
is an
almost positive
indication of
failure of
one or
more parts
of the
system. This
smell, however,
can also
originate at
the plumbing
vent. In
either case,
further investigation
is warranted.
If
you see
such signs,
a dye
test may
confirm your
suspicions. For
this test,
a special
strong dye
is put
in the
system -
usually by
flushing it
down the
toilet. A
significant amount
of water
is then
washed into
the system.
If there
is "breakthrough",
the dye
will become
visible on
the ground
surface. If
the dye
is seen
on the
surface, this
would be
a very
strong indication
that the
system has
failed. Your
Home Inspector,
a licensed
professional engineer,
or a
septic system
contractor can
usually perform
this test
for you
if it
is needed.
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If
I Plan
on Repairing,
Installing,
or Replacing
A System,
What should
I expect?
There
are two major
factors involved
in adding a new
system or repairing
or replacing an existing
one. The first
is the cost;
the second is
the inconvenience
of possibly
not being
able to use the
existing system
while a replacement
is being
installed. For new
construction, the
second
factor is not
usually a major
consideration.
Repair
or replacement
cost will
obviously depend
on what
has to be repaired
and/or replaced.
If the repair
does not involve
the leach field,
the cost may
be high, but
it will probably
not be exorbitant.
The least
expensive repair
will be associated
with a broken
pipe between the
distribution box
and
the house. The
cost for this
type
of repair is in
the order
of several hundred
dollars. If only
a septic tank
needs
to be replaced
- and the leach
field is still
undamaged - the
cost will be in
the order
of about $1500
to $2500. If a
new
leach field
is needed, and
there
is room for such
an installation,
you should plan
on
spending an
additional $2000
to $3000 for a
typical home.
If there is
not sufficient
room
for a new leach
field, the existing
field, including
the clogged soil,
must be removed
and a completely
new system must
be
installed. Such
an
effort can easily
exceed $10,000.
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If
my Family
is Growing
and I
add a
New Bedroom,
What
Should
I Expect?
Septic
systems
are designed
to dispose
of household
biological
waste.
The amount
of waste
to be handled
depends
on
a number
of factors.
Among these
are the
number
of people
living in
the
house and
their
lifestyle.
After
many years
of experience,
a major
guideline
in determining
the size
and
capability
of a septic
system has
been
correlated
to the
number of
bedrooms
in a house.
The number
of bedrooms
typically
determines
the
number of
people generating
waste and
hence
the amount
of waste
that must
be handled.
If your
family
is growing
and a
new bedroom
is needed,
then the
load
on the septic
system is
also
increased.
If the
septic system
capability
does not
keep up
with the
increased
demand,
system failure
may occur.
So,
how do you
determine the
septic system
needs for
your growing family?
The following sections
deal mainly with
sizing a septic
system so that
it can adequately
perform the desired
function. Your design
professional can
handle
the actual
testing and number-crunching
- but we have
provided some
standard guidelines
developed by New
York State to
aid you in discussing
your options with
your
contractor. You
may
not need
all this information,
but it could
help in making
your decisions.
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How
Big Should
a Septic
Tank Be?
Septic
tanks are sized
according to
the
amount of liquid
waste they
must process.
This
is
done by counting
the number
of bedrooms.
In
New York State
the minimum
size
tank
that can be
installed
now is 1000
gallons
for a 1, 2,
or 3 bedroom
house.
For each bedroom
after 3, add
250 gallons
to the
size of the
tank.
If a garbage
grinder is in
the kitchen
sink,
it counts as
an
additional bedroom.
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How
Big Should
the Leach
Field
Be?
Determining the
required size
of a leach field
is a bit more
complicated. The
first thing to
consider is the
nature of the
soil in which
the leach field
is to be constructed.
Because water
has to be absorbed
in the soil, we
need to know how
fast it can be
absorbed. This
is called the
percolation rate
and is expressed
as the time it
takes for water
in a test hole
to decrease in
level by one inch
(minutes/inch).
We must also know
the type of soil
and whether seasonal
changes in the
natural level
of groundwater
will interfere
with the satisfactory
operation of the
system. Seasonal
groundwater must
be more than four
feet from the
bottom of the
leach field trenches.
Judgments regarding
the soil conditions
and percolation
rates are best
left to a professional.
If the soil percolates
very fast (less
than one minute
per inch) or very
slow (greater
than 60 minutes
per inch) it will
not be possible
to install a standard
leach field in
the existing soil.
We must now determine
the amount of
water that has
to be absorbed
each day. As with
the septic tank
sizing, there
are also "rules
of thumb" that
can be used to
find out how much
water must be
absorbed each
day for each bedroom
in the house (expressed
as gallons per
day per bedroom).
For older houses
(built before
1979) we must
allow 150 gallons
per day (gpd)
per bedroom. For
houses where the
toilets are limited
to no more than
3.5 gallons per
flush and the
faucets and showerheads
are limited to
3 gallons per
minute or less,
we must allow
130 gpd per bedroom.
For houses with
water-saving toilets
that use only
one gallon per
flush we allow
90 gpd per bedroom.
The required flow
rate is found
by multiplying
the appropriate
flow by the number
of bedrooms (in
this case, we
do not have to
count a garbage
disposal as a
bedroom).
Knowing the rate
at which water
can be absorbed
by the soil (the
percolation rate)
and the flow rate
(in gallons per
day), we can use
the following
table to calculate
how many square
feet of absorption
field is needed.
Absorption Percolation
minutes per inch
1
- 5
6 - 7
8 - 10
11 - 15
16 - 20
21 - 30
31 - 45
46 - 60 |
Application
Rates Gallons
per Day
per Square
Foot
1.2
1.0
0.9
0.8
0.7
0.6
0.5
0.45 |
Soil with
a percolation
rate less
than 1 minute per inch or more
than 60
minutes
per inch
is unsuitable
for a conventional system.
Required Area (square feet)
= Flow Rate (gallons per day)
/ Application
Rate (gallons per day per square
foot)
Now that we know the number
of square feet of absorption
field that is needed,
we can divide by the width of
each trench to see how many
feet of trench
is required. The normal trench
width is two feet.
Let's do a sample calculation
to see how this works. Assume
you are buying
a 3-bedroom house that was built
in 1971. The leach field has
failed and
a new one must be installed.
You have had a percolation test
performed and
the design professional has
determined that the soil is
suitable, the groundwater
conditions are acceptable, and
the percolation rate is 32 minutes
per
inch. How big an absorption
field will be needed?
Since the house was built before
1979, the flow rate is 3 bedrooms
times
150 gallons per day per bedroom,
or 450 gallons per day. From
the table
above, the application rate
is 0.5 gallons per day per square
foot for
a percolation rate of 32 minutes
per inch. The required trench
area is
then 450 gallons per day divided
by 0.5 gallons per day per square
foot.
You will need 900 square feet
of absorption area. If the absorption
trenches are
2 feet wide, you will need a
total of 450 feet of absorption
trench.
Most health codes limit the
length of any one trench (called
a lateral)
to no more than 60 feet, the
minimum number of laterals is
450 feet divided
by 60 feet per lateral, or 7.5
laterals. Where property conditions
permit,
it is best to keep the laterals
the same length, so your design
professional
may specify 8 laterals, each
60 feet long. But what if there
is only room
on the property for laterals
that are 45 feet long. In this
case, you
would need 10 laterals, or trenches.
In addition to the area needed
for the leach field, you should
also allow
room for possible expansion
(50% expansion area is required
in New York State).
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What
is Gray Water?
Gray water is usually water
from a laundry system, perhaps
the effluent
from a sump pump, the foundation
footing drains, roof runoff,
and sometimes
shower drains. This water
usually does not contain human
waste
products and does not need
to be digested like
human waste. The disposal
requirements for this type
of water are less
stringent than those for human
waste. If there
is a space problem on your
site, it may be possible to
segregate
the gray
waste from the human waste
and minimize the size of the
system
needed for
control of the human waste.
Your design professional (Licensed
Engineer or
Registered Architect) can
advise you of your options
in this
area.
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Alternative
(Other Types of) Systems
The system discussed above
is a conventional system
installed in the soil
that
exists on the site. Where
the
site conditions do not
lend themselves
to installing this type
of system, there are alternatives.
For example, if ground
water or percolation
rates are
unsuitable, it may be
possible to install
what is called
a "mound" system.
In a mound system, a
suitable soil is placed
above the
unsuitable soil.
A conventional system
is then installed in
the mound.
There are some additional
requirements for this
type of design.
If there is not enough
room for a conventional
leach field,
it may be
possible to install one
or more cesspools, or
seepage
pits.
These units are usually
round, require less open
ground, and are deeper
than a conventional
leach
field. Again, there are
specific requirements
for these systems.
Conventional, mound, and
seepage pit systems all
work by what
is called
anerobic bacterial action.
This means the bacteria
work without
oxygen.
Some systems are designed
to be aerobic - meaning
the bacteria
need oxygen
(air); There are also
hybrid systems that use
a combination
of anerobic
and aerobic sections.
Your design professional
will advise you if one
of the non-conventional
systems is best for your
needs.
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