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Checking Frozen Septic Systems to Prevent Future Problems
Sara Christopherson, Minnesota
Extension Educator
Ken Olson, Minnesota Extension Educator
Jim Anderson, Professor and Extension Soil Scientist, Department of
Soil, Water and Climate, University of Minnesota
Dave Gustafson, Minnesota Extension Educator
If an onsite septic system freezes during a cold winter, it is important
to know why and where the system froze. This will help determine if
repairs, corrections, or changes to the system are necessary to make
sure it will operate properly in the future. The steps needed depend
on the type of system and where the freezing occurred. If the freezing
problem was simply because of cold temperatures and/or lack of snow
cover to insulate the system, it may just need to be checked for problems
and perhaps minor repairs or improvements made. However, some freezing
problems are the result of problems with the design, installation, or
use of the system that may require significant repairs or changes to
solve the problem.
Other factors, such as excessively high or very low water use can also
be a contributing factor to the freezing problem. For more information
about why systems freeze and measures to prevent freezing, please see
the fact sheet entitled Freezing Problems with Onsite Sewage Treatment
Systems, found at http://septic.coafes.umn.edu/Homeowner/
There are four common locations where systems can freeze.
- Pipe from house to tank
- Septic tank and/or pump tank
- Pipe to soil treatment area
- Soil treatment area
It is important to determine where and why the system froze so corrective
actions can be taken to avoid freezing in future winters. A licensed
onsite sewage treatment professional should be able to determine where
the system froze if it is not obvious. Homeowners should also know where
each component of the system is located to aid in problem solving and
proper maintenance. After a system has been frozen and thawed each component
should be checked.
1. Pipe from house to tank
If the pipe between the house and septic tank froze, two issues need
to evaluated. First, make sure there are no leaking fixtures, such as
toilets or faucets, or low wastewater generating devices, such as a
high efficiency furnace discharging into the system. Secondly, make
sure the entire pipe has sufficient slope without any sags to assure
water is draining into the septic tank (minimum of 1" drop in eight
feet and a maximum 2" in eight feet).
2. Septic tank and/or pump tank
When a septic tank freezes, the baffles need to be checked to verify
that they are still in place and have not been damaged. The tank(s)
should also be checked for cracks, although this occurs very rarely.
Styrofoam which is designed to be buried can be placed over the tank
to insulate it by removing the soil cover, placing 1-3 inches of Styrofoam,
and replacing the soil cover. If the tank was pumped out because of
a freezing problem and this pumping was not done through the manhole
(>20 inches in diameter), then proper maintenance of the tank was
not performed. In this case, the tank should be pumped on its normal
2-3 year interval from the last date of proper maintenance.
If there is a pump in the system, it should be inspected to make sure
that the floats have not been damaged. The pump should be checked to
assure it is pumping effluent and that it will turn off and on as necessary.
It is important that the pump is accessible at all times. This may require
the installation of a riser to bring the access to the surface. Because
bringing the manhole to the surface will allow more heat loss from the
tank, it is a good idea to add Styrofoam under the manhole cover or
place insulation (loose material such as straw, hay or leaves) over
the top of the cover each fall.
3. Pipe to soil treatment area
The pipe from the tank to the soil treatment area may have frozen for
the same reasons as the pipe from the home (# 1). If so, the same remedies
would apply. In addition, if there is a pump in the last tank, it is
critical that when the pump shuts off, all the effluent drains back
into the tank through a weep hole. A weep hole is typically a ¼-inch
hole in the lowest portion of the piping in the manhole. This weep hole
will drain water even when the pump is on. Two common problems in pump
tanks are check valves that do not allow effluent to drain back and
pumping systems designed for drainback through the pump. A licensed
onsite sewage treatment professional can determine if a check valve
is in place or if the effluent is draining through the pump.
4. Soil treatment area
If the soil or mound was soggy or wet before the winter, the system
needs a thorough evaluation by an onsite sewage treatment professional
to determine why it is not operating properly. If sewage comes to the
surface while frozen in the winter, this creates a health risk to people
or animals that come in contact with it. This problem is serious
and must be corrected. If ignored after the freezing problem, sewage
is likely to surface in this area in the future. The solution may be
as simple as bringing in additional topsoil or a more extensive reworking
of this part of the system. Checking the distribution system should
also be done. In gravity situations drop or distribution boxes should
be checked and in pressure applications the system should be verified.
If a drip distribution system froze, a licensed onsite sewage treatment
professional trained to maintain the system should troubleshoot the
system to determine if a problem exists. Common reasons for drip systems
freezing include improper drainback and frozen air relief valves.
For More Information
Please see our website at:
http://septic.coafes.umn.edu/homeowner/index.html
for more information about proper operation of septic systems. You can
also contact our staff by calling 800-322-8642.