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Odor Issues with Onsite Sewage Treatment Systems
Sara Christopherson, Minnesota
Extension Educator
Ken Olson, Minnesota Extension Educator
Dave Gustafson, Minnesota Extension Educator
Jim Anderson, Professor and Extension Soil Science, Department of Soil,
Water, and Climate, University of Minnesota
Occasionally, homeowners complain about odors from their onsite sewage
treatment system. Although most people understand that sewage has a
particular odor, steps can be taken to limit these odors in the home
and yard. Gases from an onsite system that can be a problem include
hydrogen sulfide, carbon dioxide, and methane. Within a home these gases
can be irritating, toxic and explosive. In a yard they are not typically
found in high enough concentrations to be dangerous, but are still a
nuisance.
There are several locations within an onsite system where odor can
be an issue.
- In the home
- Near the septic tank
- Near a pretreatment unit
- Near the soil treatment area
- In the yard
1. Odors in the Home
Septic odors inside the house are both annoying and can be a health
problem. Odors in a home are typically an indication of a plumbing problem.
A very common problem is the drying out of a trap in a basement floor
drain allowing gases from the septic tank to vent back into the home.
This can be corrected by making sure all floor drain traps are periodically
filled with water. Also, the cleanout access plug inside a drain may
be loose and could allow for sewer gas to escape. A plumber or ISTS
professional who provides line cleaning could check this out and correct
the problem.
A second common problem is the plumbing vent located on the roof, which
allows the pressure in the drainpipes to equalize as wastewater flows
through them. Without this vent, sinks, tubs, and toilets gurgle, traps
dry out, and odors come into the home. These plumbing vents can freeze
closed during prolonged cold periods or get clogged with leaves or other
debris. A warm day or two will thaw out the frozen pipe, but leaves
will need to be cleaned out. The pipe can also be unfrozen using a jetter
or warm water, but always be sure to take special precautions when working
on a slippery or steep roof.
A third common plumbing problem is an improperly sealed cover on an
ejector sump pump basket in the basement. The cover should be checked,
and a new seal applied to prevent leaks.
2. Odors near the septic tank
An occasional weak odor near the septic tank may be quite normal. But,
if there is a particularly strong odor around the septic tank(s), the
first step should be to make sure all manholes and risers are securely
covered. Typically, a concrete lid covers the tank manhole, although
other materials such as plastic and metal lids are used. The septic
tank manhole can be covered with a maximum of 12-inches of soil or can
come to the surface, while any manhole on a tank with a pump must come
to surface to allow for repair or replacement of the pump. The newer
plastic lids have a rubber seal which helps keep odors in the tank.
They must also be properly secured in place with lag screws or other
fasteners. If a concrete lid is leaking odors out of the manhole, weather
stripping or other materials can be used to create a temporary seal
that will contain odors but still allow for proper maintenance of the
tank. This seal will need to replaced after maintenance.
3. Odors near a pretreatment unit
There is a growing use of pretreatment units in onsite sewage treatment
systems. The most common pretreatment devices are aerobic treatment
units; constructed wetlands; and peat, recirculating, sand, and textile
filters. If an odor is persistent around one of these pretreatment units,
a licensed onsite professional trained to maintain the specific type
of unit should be called.
4. Odors near the soil treatment area
If there are strong odors in the soil treatment area (around an in-ground
drain field, bed or mound), it can indicate a problem with that part
of the system. All inspection pipes should be checked to make sure the
pipes are not broken and that they are covered. A visual inspection
of the entire area should be performed to determine if there are any
wet or spongy soil areas indicating that sewage is coming to the surface.
If any of these conditions are found, humans and animals can come in
contact with it. This is considered an “imminent health threat”
and should be corrected immediately.
5. Odors in the Yard
If the yard in general smells of septic gas, it may be that the plumbing
vent pipe (described in # 1 above) on your house or a neighbor’s
house needs to be extended to diffuse the odors. Homes located in valleys,
forested areas, or low areas may not have appropriate wind patterns
to carry the odors away from the living areas and the yard. As the wind
blows over the house, the air currents that are supposed to carry the
gases up and away can instead carry the sewer gas down into the yard.
Extending the vent pipe can help diffuse the odors carrying them away
from the yard. Carbon filters can also be placed on the top of the vent
to help control odor. The filters need to be changed regularly (every
1 to 5 years) to be effective. According to the Minnesota Plumbing Code,
a device such as a filter is not allowed obstruct the flow of air, therefore
the filter must be chosen in accordance with these regulations. Check
with the local unit of government if clarification is needed.
For More Information
Please see our website at:
http://septic.coafes.umn.edu/homeowner/
for more information about proper operation of septic systems. We can
be reached by calling 800-322-8642.