A septic tank is designed to remove the solids found in wastewater from
a Privately Owned Wastewater Treatment
System (POWTS). These solids are what cause failure in most
cases as they collect in the systems discharge bed and form an
impermeable layer, known as a bio-mat. Once the bed is "clogged" with
solids, costly renovations must be made. The more solids that can be held
in the septic tank, the longer the system will function properly.
The inlet and outlet in these tanks are located near the top of the
units. Both the inlet and outlet are covered with a baffle that extends
down to the effluent. these baffles help reduce solids output. Most
solids will settle on the bottom of the tank. Then solids are then
partially consumed by anaerobic bacteria. Remaining solids are removed by
pumping.
Greases, oils and suspended solids (solids held suspended in the waste
water) form a scum layer at the top of the tank. This layer is held in
the tank by the baffle over the outlet of the tank. In the center of the
tank a clear layer of effluent forms. The outlet baffle is placed so that
discharge from the tank comes from this clear layer. Most studies
indicate that septic tanks will remove about 50% of the solids that flow
into it. This varies from system to system based on total flow during the
day, and total rest time during the day.
Assuming an average flow system, one tank will remove 50% of the solids,
a two tank system will remove 75% of total solids, etc. There are also a
number of filters that can be installed in a tank to reduce solid output.
See Zabel Filters. Another aid in
reducing
solid output is multiple chamber tanks. These are septic
tanks having
more than one chamber. Lake Shore offers several tanks with
this
configuration. See the 1200 Gallon, 1000/750 Gallon,
1200/1000
Gallon two compartment tanks.
Tanks should be pumped every two years. Current research
indicates that
this frequency is optimal. Pumping more often results in
reduced bacterial
action. Pumping less frequently will result in smaller
solid settling
distance and higher solids output. Any filters installed in
a tank must
also be cleaned regularly. See manufacturers recommendation
for proper
cleaning schedule.
Current Wisconsin regulations require a soil test be performed to
determine what type and size of a POWT (Privately
Owned Wastewater Treatment System)is
required.
Currently the two most predominate types of systems in
Wisconsin are
Conventional and
Mound wastewater disposal systems.
This test
must be performed by a Certified Soil Tester/Morphological
Evaluator. These evaluators hold
licenses which are issued after passing an exam
administered by the state
of Wisconsin. This certification program and soil
evaluation procedure is
relatively new to the State of Wisconsin.
Prior to the institution of soil testing, a percolation or
"perc" test
was performed. This procedure involved digging a hole in
the ground,
filling it with water, and timing how long it took to drain
or percolate
the water into the surrounding soil. As time passed, more
and more systems
were failing prematurely. It turned out that many "perc"
tests were
performed on poor soils and were done in late summer and
early autumn
when ground water was low. This would ensure the property
would pass for a
conventional system. Well as you may be aware, water levels
in the soils
of Wisconsin vary greatly during the year. In spring, due
to snow and
frost thawing, levels are at a yearly high in many areas.
These levels
recede until winter frost sets in and the cycle starts
again. Soils that
are dry and capable of absorbing effluent from a septic
tank during late
summer and early fall may be completely saturated early
each year and
not suitable for treating wastewater in spring and early
summer. This
"perc" test also failed to consider a number of other
important and
neccessary factors in determing whether soils present were
capable of
treating wastewater effectively year round.
In response to the shortcomings of the "perc" test, the
current soil
testing regulations were developed. Limiting factors such
as high seasonal
groundwater (less than three feet from surface ANY TIME
DURING THE YEAR),
high bedrock, soil being disturbed (land fills, compact
soils, etc.) are
now considered as part of the evaluation. Other factors
must also be
weighed. These include the clay, silt and sand content of
the soils, soil
structure, soil profile, mottling (discoloration due to
seasonal changes
in ground water levels), etc. are also factored into the
evaluation. All
of these factors determine what type of POWTS is to
be installed.
Some parcels of property will not allow for any
POWTS to be built
and you may have to install a holding tank or not be
allowed to build at
all. Many local communities will not allow a holding tank
to be installed
for new construction.
Please note that if you have an existing system that needs
to be
replaced, the state of Wisconsin will waive some or all of
these rules to
allow a replacement system to be installed. These
experimental systems
include aerobic treatment plants, sand filters, and
modified mound
systems, or a holding tank. These systems may be included
as a standard
POWTS in new regulations now under consideration.
Currently a
waiver from the State may be required. Talk to your local
soil tester or
installer. The state cannot condemn your property because
of poor soils.
Also, if you are forced to build your home with a holding
tank, once you
occupy the house you may be able to obtain a waiver to
build a POWTS.
Mound systems, conventional "septic" systems, in-ground pressure
systems, at-grade systems, trench systems, etc. are all types of systems
used to treat wastewater
from structures not served by public sewer. They all do
basically the same
thing, they are just designed differently to compensate for
differing lot
constraints and soil conditions. A MOUND SYSTEM refers to a system in which the
soil absorption part
of the system must be designed and installed literally on
top of the existing
grade to assure the wastewater is properly treated on sites
that have
high groundwater or bedrock. In all Privately Owned Wastewater
Treatment Systems (POWTS), including
both mound and conventional systems
in Wisconsin, the wastewater exits the house and enters a
septic tank
where the water is partially treated. In a septic tank the
inlet and outlet of
the tank are both near the top of the tank, allowing the
larger solids to settle
to the bottom of the tank. A portion of the solids
accumulating on the bottom
of the tank are eventually "broken down" by anaerobic
bacteria, and the
balance pumped out when you have your system periodically
pumped.
Greases, oils, and lighter solids which float on the top of
the water in
the tank are prevented from exiting ( which leads to
clogging of the soil absorption
bed), by baffles which cover both the inlet and the outlet
of the tank,
allowing only relatively cleaner water near the middle of
the tank to exit. Remember: both conventional septic systems and mound
systems
begin by having the wastewater partially treated in a
septic tank and
must be periodically pumped for proper maintenance. After the partially treated water exists the septic tank
the water may
follow gravity into a conventional (below grade)
soil absorption
bed, or flow into a pump tank to eventually be dosed into a
mound system under
pressure. A mound system in Wisconsin is a pressurized equal
distribution
system, which means when water is "dosed" to the mound
(four times max in a 24
hour period) the wastewater is equally distributed under
pressure. This means
you use the entire square footage of the mounds soil
absorption area
to treat the water. The pressurized equal distribution is
due to the
distribution pipes in the mound being only 1" to 1&1/2" in
diameter with
small, specifically sized holes drilled at specific
spacings. This
assures the most equal distribution possible.
A conventional septic system is an in-ground gravity discharge
Privately Owned Wastewater Treatment
System (POWTS). This system will consist of one or more
septic tanks and a gravity discharge feed bed or series of trenches.
Characteristics of the soils will be high sand and gravel content along
with low levels of clays and silts. Seasonal high ground water and
bedrock levels must also be at least three feet below the discharge pipe
in the trench. These soil characteristics have to be evaluated by a
certified soil tester.
In a conventional system, the wastewater exits the home and enters one or
more septic tanks. The inlet and outlet of these tanks are located
near the top so to allow solids in the wastewater to settle to the
bottom. This is the septic tanks primary function, to keep the solids
from leaving the tank. These solids are later partially broken down by
anaerobic bacteria. Remaining solids are removed by having the tanks pumped.
Pumping should be done every two years.
After the effluent leaves the tanks, it is gravity discharged to a
"leech" field or series of trenches. A trench system has the best
performance characteristics, but requires a much larger area. The "leech"
bed is most common. In both systems the effluent passes through the
native soil on its way to the ground water. This is why there must be 36"
inches of soil between the bottom of the discharge pipe in the bed or
trench, and any ground water or bedrock present. After the water passes
through this layer of soil it has been purified enough that it may be
added back to ground water without posing a health hazzard.
Most of these beds are constructed in the field utilizing clean stone and
perforated PVC pipe. There are also performed plastic chamber on the
market such as Infiltrator. These chambers offer unique
performance characteristics that enhance installation and overall systems
performance.
This type of system is the most inexpensive discharge system available.
However many areas do not have the native soils present to allow this
type of system. Talk to your installer or soil tester about what would be
best for your lot. If you are currently looking at a piece of property,
you should know what type of system you will be able to install.
A new feature to Privately Owned Wastewater
Treatment System (POWTS) are new emerging
technologies. These systems are not covered by current administrative
code ILHR83. The State of Wisconsin's Department of Commerce
recognizes that current code is outdated and does not take into
account new technology developed in the last decade. The department, in
conjunction with other regulatory agencies, the legislature, private
industry, environmentalists, and a host of others is currently working
on a new code that will allow new treatment systems to be tested and then
made availible to homeowners. These systems will include aerobic
treatment plants, sand filters, peat moss treatment, constructed
wetlands, and the list goes on.
Many of these new systems are still in the development and testing stage.
The Department of Commerce, the University of Wisconsin-Madison's
Agricultural department and private industry are working on numerous
projects testing these projects. Many of these tests are being conducted
on private homeowners properties where the existing system failed and the
native soil and site characteristics would only allow a holding tank to
be installed.
Up until recently, most POWTS relied on the discharge bed to perform
treatment of the effluent. These new technologies all have one thing in
common. These systems pretreat effluent before discharge to the soil.
Aerobic treatment plants work in similar fashion to municipal wastewater
treatment plants. The effluent is held while large quantities of oxygen
are injected. the oxygen allow for aerobic bacteria, bacteria requiring
oxygen to survive, to consume the solids in the effluent. This bacteria
is much more effective than anaerobic bacteria, bacteria not needing an
oxygen source. Most aerobic units have been tested by the National
Sanitation Foundation, NSF. A NSF class one rating is the highest issued
and probably the type you want to pursue.
Sand filters inject effluent in measured quantities through a layer of
sand. This allows also for aerobic bacterial action, discussed above.
Sand filters can be single pass or recirculating. Single pass sand filtes
require a larger area and more material. Recirculating sand filterss are
smaller and easier to construct. Sand filters can be made of several
types of materials. These materials can be course sands or fine stones.
These materials must be clean.
Other types of systems such as peat moss beds, constructed wetlands,
subsurface drip irrigation's systems, etc. are also availible. If you are
having problems getting a POWTS approved for your lot or home you may
want to talk to a soil tester, installer familiar with these systems, or
a representative of Lake Shore Burial Vault. We would be glad to assist
you in finding the most effective and inexpensive system available.
A certified soil tester must complete a detailed
analysis of your
soil characteristics (and other site limitations i.e. set
backs, slopes, etc.)
to determine the type of system your lot requires. The most
important
item the soil tester is looking for is depth to a "limiting
factor" such as
high groundwater or high bedrock. Wisconsin administrative
code ILHR 83
(at this time) mandates a 3 foot vertical separation
between the bottom of
the soil absorption system and high groundwater or high
bedrock in most
instances. Example: If the soil test determines that you are in
suitable soil and
the highest groundwater is 70 inches
in the ground, 3 foot vertical separation would put your
"system
elevation" (or bottom of soil absorption
system) 34" deep in the ground. A subsurface "gravity"
system is what
most people consider to be
"conventional": a system in the ground. If that same soil test showed the limiting factor at
only 24 inches
below the ground surface, how would
you design a system to acheive the minimum required 36 inch
vertical
separation? By artificially creating
the bottom of the soil absorption system 12 inches
above the
ground by placing 12 inches of a medium
washed sand over the top of the ground and then installing
your
distribution bed of stone and piping on top
of the sand. When this system is covered up with topsoil it
creates a
mound, because it's designed
from the ground up instead of below the surface of the
ground.
All on-site waste water disposal systems are "progressively failing systems".
They will all fail at some point in time and you will have to
completely replace the system whether it is a conventional or a mound.
Sysems fail due to the accumulation of solids in the waste water disposal
field preventing the effluent from passing into the soils or mound. This
accumulation of solids is known as a "bio-mat". When a system fails the
wastewater backs up into your house, this occurrence being known as a
"floor-event", or discharges onto the surface above the system, this
occurrence being known as a "lawn event". Both events are the last
warning signs that your system has now failed.
Specific dimensions and cited requirements refer to
Wisconsin
Administrative Code ILHR83. This is not to imply that this
website has
been reviewed, approved, or recognized by any regulatory
agency.
What is a soil test?
Specific dimensions and cited requirements refer to
Wisconsin
Administrative Code ILHR83. This is not to imply that this
website has
been reviewed, approved, or recognized by any regulatory
agency.
What is a mound system?
What is a conventional system?
Specific dimensions and cited requirements refer to Wisconsin
Administrative Code ILHR83. This is not to imply that this website has
been reviewed, approved, or recognized by any regulatory agency.
What other systems are available?
Specific dimensions and cited requirements refer to Wisconsin
Administrative Code ILHR83. This is not to imply that this website has
been reviewed, approved, or recognized by any regulatory agency.
How do I decide what type of system I need?
Specific dimensions and cited requirements refer to
Wisconsin
Administrative Code ILHR83. This is not to imply that this
website has
been reviewed, approved, or recognized by any regulatory
agency.
Do's and Don'ts!
System life is dependent on several factors. Water flow, types of solids
disposed of, discharge of non-biodegradeable items to the system are but
a few. Understanding of how a system works and what types of solids it
can and cannot handle are essential to system life. Private on-site
wasterwater disposal systems can last 20-30 years or more if properly
maintained. Please refer to Mound Systems
and Conventional Systems for more details
on these systems.