| Absorption
Area/Leaching Field
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| The absorption area is a system of subsurface piping, known as
lateral lines, that forms a series of water-carrying channels into which
the effluent is discharged for direct treatment and absorption into the
soil. 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. The natural soil conditions will need to be able to dissipate and
disperse the discharged effluent without becoming oversaturated. It
should also provide enough capacity to store effluent during periods of
unusually heavy use or when rainfall or subsurface flooding reduces the
ability of the system to disperse and distribute the liquid. The most readily, noticeable sign that an absorption area has failed
is “breakout.” When this occurs, you will notice ponding water
laying on the soils directly above the individual lateral lines. 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, for example-this
may be an indication that the leaching field is failing. The smell may
also be accompanied by a "spongy" feeling in some areas of the
leaching field. |
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| Backfill |
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| Backfill is clean soil, free of debris or large organic material,
that is used to fill the lateral trench lines after the gravel and
piping is installed. The backfill needs to be finish-graded so that
surface water does not pond above the lines. |
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| Blackwater/Septage
Outlet |
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The point at which the drain/waste pipes for the bathroom
plumbing connect and leave the house structure is the blackwater outlet.
In typical on-site waste disposal systems, there is usually only a single
primary septic tank that all of the plumbing drain lines empty into. This
includes toilet, as well as sink, shower, and tub waste. In most cases,
when looking for the blackwater drain outlet, you will find a drain line
of approximately 4-4 ½ inches in diameter exiting the foundation wall, to
which all of the other drain lines lead into. |
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| Bouyant
Waste |
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| The buoyant waste is made up of greases and soaps from the graywater
waste. When a septic tank is opened, this is usually the first thing
that is seen floating on top. If periodic maintenance is not performed
(i.e. pumping the tank clean every 2-4 years), this waste can build up
to the point of going above the top of the inlet and outlet tees and
clogging the inlet into the tank, as well as possibly clogging the soils
in the absorption area. |
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| Distribution
Box |
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| When the effluent leaves the septic tank, it is sent to the
distribution box (D-box). The D-box usually has a single inlet (from the
tank) and several outlets that lead to the individual lines in the
absorption area. The D-box will usually have one or more separate
baffles that reduces the velocity of liquid moving through the D-box to
allow more even displacement of the liquid effluent into the separate
lateral lines. |
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| Exterior
Cleanout |
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| For ease of maintenance and inspection, most properties with
private on-site waste disposal systems will have an additional
cleanout pipe and access installed to aid in removing waste from the
septic tank without having to actually excavate the main tank access.
The cleanout is usually made of 4-inch diameter PVC or cast iron
piping with a screw-on cover. The cover is usually flush with the
finish grade or extends up high enough to be noticeable so as not to
be run over with yard equipment. If there is sewage backup in the home, it can be a possible sign of
a failing system. However, backup can also be the result of a blockage
somewhere between the house and the septic tank. |
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| Gravel
Bed |
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| The gravel bed is crushed or screened stone
that comes from river sand or is quarried. The open porosity of the
gravel allows rapid dispersal of the liquid effluent. The gravel bed is
laid at the bottom of the lateral line trench, with the actual lateral
plumbing line sandwiched within the gravel. |
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| Graywater
Drain Connection Tee
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| There are usually two ways that graywater waste can be treated and
disposed; one way is through its own absorption area and another is to
tie into the primary waste system. When the graywater discharge is tied
into the primary house waste system, the outlet line should be tied into
the primary drain line of the main waste system. This connection can be
located between the foundation exit and the main septic tank itself. |
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| Graywater
Outlet |
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| In some specialized cases, there will be a separate septic tank for
graywater waste. These systems are usually for the kitchen and laundry
plumbing, and sometimes the bathroom sinks.The graywater outlet will usually be constructed of 2 or 3-inch
drain pipe. Like the blackwater outlet, the point where the drain line
exits the house may serve as an indication of where the graywater tank
is located, but not always. |
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| Graywater
Tank |
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| When the disposal of blackwater waste and graywater waste is
separate, there will be a separate tank installed for the graywater
waste. This tank is usually made of the same materials as the main
septic tank, however, it can also be made of other materials such as
metal, plastic, fiberglass and concrete. This tank is usually smaller in
size than the primary septic tank. The interior components of the graywater septic tank are similar to
those of the larger septic tank, with inlet and outlet tees, baffles,
access covers and tank connections. The graywater tank may be connected
to the primary septic tank and absorption area, or it may discharge into
its own absorption area. |
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| Graywater
Waste |
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Graywater waste is defined as the wastewater produced from baths and
showers, clothes washers, lavatories, laundry systems, perhaps the
effluent from a sump pump, the foundation footing drains, and sometimes
roof runoff. This waste usually contains significant amounts of soaps
from personal hygiene, dishwashing and laundry, as well as greases and
oils from cooking. If a dishwasher or garbage disposal is used, there
will also be food solids present. Because the bacteriological farm has
greater difficulty breaking down undigested food material, a separate
collection tank aids in the efficiency of the main waste system. Also,
soaps and greases can prematurely saturate and rapidly clog the main
absorption area if they manage to reach it. Graywater 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.
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| Inlet
Tee |
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| All septic tanks have an opening for the waste to enter the tank and
another one for the waste to exit the tank. The entrance is called the
inlet. Inside the tank there will be either a PVC or metal, tee-shaped
fitting, consisting of a short section of horizontal piping leading into
a slightly longer, vertical section of piping that is open on both the
top and the bottom. The bottom of the tee is usually below the level of
the bottom of the outlet and is inside the liquid effluent layer. This
is to prevent any buoyant waste from backing up into the house side of
the drain lines and into the house plumbing. |
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| Leach
Line |
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| Leach line piping is usually made of perforated piping, approximately
four inches in diameter. The piping is laid in a bed of gravel at the
bottom of a series of interconnected trenches. The gravel is then
covered by a layer of backfilled soil that covers the trench system.
Some older septic systems actually used a series of segmented,
non-perforated tubes set in a bed of gravel, with the tubes set between
½ inch and 1 inch apart. These tubes were sometimes constructed of a
thickened roll of asphalt-saturated fibrous material (similar to
building felt paper), or they were made of an orange ceramic tile
material, similar to clay flue tiles. Both of these materials have been
found to deteriorate and collapse. |
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| Leach
Line Trench |
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| Any single trench in an absorption area is called a lateral line.
Where property conditions permit, it is best to keep the laterals the
same length, with the number of laterals being determined by the needs
of the house. The trenches are approximately 2 to 3 feet wide, 3 to 4
feet deep, and about 9 feet apart. Some modern systems may have
shallower trenches. The trench should be sloped enough so that the liquid effluent flows
fast enough to allow for even dispersal. A grade of one to two inches
within eight feet is what is commonly used. If the slope is too flat,
the effluent may stall close to the distribution box and cause premature
saturation. If the slope is too steep, the effluent may run to the end
of the lateral line and, again, cause premature saturation. |
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| Liquid
Effluent |
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| The liquid effluent is made up of the remaining liquids and
semi-buoyant waste particles after the sludge and buoyant waste have
separated. A normally operating septic tank maintains a constant
effluent level at the height of the bottom of the outlet tee opening.
Consequently, when new waste enters the tank, the liquid effluent level
rises and the effluent is forced out of the tank through the outlet into
the distribution box and into the absorption area for dispersment and
continued treatment. Septic tank effluent is usually cloudy and contains suspended solids
and pathogens, including disease-causing bacteria and viruses. This
condition requires more bacterial action for treatment than can occur in
the tank alone. |
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| Outlet
Tee |
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| All septic tanks have an opening for the waste to enter the tank and
another one for the waste to exit the tank. The exit is called the
outlet. Inside the tank, there will be either a PVC or metal tee
fitting, consisting of a short section of horizontal piping leading into
a slightly longer vertical section of piping that is open on both the
top and the bottom. The top of the vertical section must extend above
the level of the scum mat, and the bottom of the vertical section must
extend below the bottom level of the scum mat. The outlet tee is usually
several inches below the level of the inlet tee. |
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| Primary
Septic Tank |
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| The septic tank is a watertight structure that is the main collection
point for human waste by-products. It is at this tank that the solid
waste is separated from the liquid waste and the biological digestion of
the waste matter takes place, referred to as part of the closed portion
of the treatment system. Until about 1965, most septic tanks were constructed of steel plates,
which were welded together. After 1965, the primary construction
materials were fiberglass or cast concrete. Septic tanks are sized
according to the amount of liquid waste they must process. A typical
sized tank is 1000 gallons for a one, two, or three-bedroom house. For
each bedroom after three, add 250 gallons to the size of the tank. If a
garbage grinder/disposal is present at the kitchen sink, it counts as an
additional bedroom. |
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| Septic
Tank Cleanout Access
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| In order to make repairs or perform regular maintenance or
cleaning/pumping of the tank, access must be provided. There are usually
two or three access hatches located at the top of the septic tank-one
located over the inlet and outlet tees, and sometimes one larger one
located at the center of the tank. |
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| Sludge
Layer |
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The sludge layer consists of the heavier waste solids that separate
and settle to the bottom. The sludge layer is where the decomposition
process continues by means of bacteriological interaction. These
bacteria live and grow without the presence of air in what is called an
anaerobic bacteriological farm. (When oxygen is introduced, this
is called an aerobic bacteriological farm.) The average
efficiency of an anaerobic bacteriological farm is approximately 60 to
70 percent. If a second tank is installed, as is becoming more
commonplace in several parts of the country, then the efficiency will be
increased. Although decomposition is a continual process, the breakdown is not
complete, which can eventually result in waste residue build-up if not
pumped out on a regular basis (every 2-4 years). This residue can build
up to the bottom of the inlet or outlet tee and block flow into and/or
out of the tank.
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| Tank
Access Cover and Riser
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When septic tanks have to be buried more than 18 inches below
finished grade, a riser or access tube/tunnel is installed on top of the
tank body above the access cover, and is extended up to a point that is
less than 18 inches from the ground surface. The riser(s) needs to be
completely sealed to the tank to prevent ground water from entering the
riser cavity, which may cause a flooding of the tank and the whole
system.
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| Tank
Baffle |
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| A baffle is a vertical section or wall within the tank that reduces
the velocity of, and directs the waste through, the tank and prevents
solids from flowing into the outlet pipe and leaving the tank. Baffles
are also installed to assist in the further breakdown of the waste by
creating multiple compartments that allow the effluent to sit and
separate longer, providing the bacteriological farm more time to operate
at greater efficiency. The sizing of the baffles is important. If the baffle or tee is not
deep enough, the floating buoyant waste may enter and plug it. If the
baffle or tee extends too deep, the downward flow of incoming waste may
cause excessive agitation within the tank and result in solids being
carried out with the effluent. If sludge or buoyant waste is forced into
the distribution box and into the leaching field, the soil will quickly
become clogged or saturated. If this happens, the liquid will no longer
percolate (absorb) into the soil. Broken baffles in the septic tank that
allow sludge or scum to escape can cause this condition. Failure to
perform periodic maintenance by having the tank pumped can also lead to
a situation where the sludge and buoyant waste overwhelm the baffles.
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