Even with attentive care and management, issues can arise. Learn how to identify some of the more common septic system issues and how to address, or even prevent them.

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Why do septic systems fail?

Sewage from homes has pathogens such as bacteria and viruses, plus nutrients, solids and cleaning products that can cause human health and environmental problems. "Failure" of a septic system means that wastewater may be allowed to come in contact with people or enter the natural environment before it is harmless.

Common indicators of a failing or failed septic system may include one or more of the following:

  • Sewage backup into the house.
  • Water or sewage surfacing in the yard or a ditch. Sewage odors indoors or outdoors.
  • High levels of nitrates or coliform bacteria in well water tests.
  • Alarms sounding/flashing on the system.
  • Frozen pipes or soil treatment areas.
  • Frequent intestinal disorders.
  • Algae blooms and excessive plant growth in nearby ponds or lakes.

Failure to properly treat sewage is most commonly the result of: improper design, installation or sizing of one or more components of the system; over use of water in the household; or lack of proper maintenance.

Improper design, installation, or sizing may be a result of mistakes by the professionals when the system was installed. More commonly, it means that the wrong system was chosen for the site and soil conditions (i.e. high water table, cesspool, etc.); or the residence has been modified to include more people or use fixtures or appliances that the system was not designed or sized to handle. Examples of this are a bedroom addition to the house or the installation of a garbage disposal.

Over-use of water is a common problem since the typical person (man, woman, or child) uses about 100 gallons of water per person per day. Systems are sized for normal volumes of water use, but abnormally high usage or accidental over-use - leaky fixtures - can easily overload a system. And partially damaged drainfield (perhaps from improper maintenance) may not be able to treat even normal water use rates. This situation often occurs when a home of one or two persons is sold to a family of five or six and water use suddenly increases.

Improper maintenance -- the solids that accumulate in the septic tank must be removed regularly. Build-up of excessive scum or sludge in the tank will cause solids to enter the soil treatment area and plug it over time. The University of Minnesota Extension Service recommendation suggests a septic tank should be cleaned (pumped) through the manhole every one to three years to remove all of the solids. The frequency of cleaning depends on several factors including the number of people in the home, the size of the tank and garbage disposal usage. The removal of all solids requires flushing and back flushing of the tank several times

By following some simple home management and maintenance practices, these failures can be eliminated.

Freezing problems

Even in a normal Minnesota winter,septic system freezing can occasionally be a problem. Identifying and correcting a potential freezing problem is far easier than dealing with a frozen system. Here are a few common causes of onsite system freeze-ups, and what you can do if your system freezes.

Odor issues with septic systems

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.

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 that provides line cleaning could check this out.

A second common problem is the plumbing vent located on the roof. It is necessary to allow the pressure in the drainpipes to equalize as wastewater flows through them. Without this vent, sinks, tubs, and toilets would 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 be unfroze using a jetter or warm water. Always 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.

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" 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.

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.

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 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.

Odors in the yard

If the yard in general smells of septic gas, it may be that the plumbing vent pipe 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 do 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, cannot 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.

The problem with cesspools and seepage pits


The presence of improperly treated sewage is a threat to public health and the environment. Human exposure to sewage has resulted in disease outbreaks, severe illnesses, and in some instances death from the bacteria, viruses and parasites contained in the waste. Wastewater disposal systems that do not adequately treat wastewater also negatively affect our lakes, rivers, and groundwater by potentially introducing sediment, nutrients, and chemicals that result in contamination. 

There is also a safety concern with many of these systems because the tank lids may collapse resulting in an unsafe environment for people, animals and infrastructure.

What is proper wastewater treatment?

In Minnesota, we are concerned about all of our water resources for both beneficial use and recreation. One way to minimize damaging our waters is to ensure effective wastewater treatment is achieved across the State.

Effective wastewater treatment is simply the removal of solids, nutrients, bacteria and viruses from the wastewater and the predictable acceptance of the treated waste into the natural environment. In the case of individual sewage treatment systems (ISTSs), this level of treatment and acceptance is fundamental to our ISTS design requirements.

Specifically what is required for this level of treatment has been researched for over 100 years and remains true today – three vertical feet of dry, well-aerated soil with a wastewater distribution network sized based on use (e.g. single family home, day care facility, etc.) and soil properties. Often times our older ISTSs placed too much importance on wastewater going away (i.e. disposal), without adequate understanding or concern for treatment.

There are two primary reasons why seepage pits and cesspools do not provide adequate wastewater treatment; size and depth. Sewage is discharged into a small diameter pit and causes the wastewater to disperse under saturated, anaerobic conditions, limiting soil treatment. The small size of these systems also increases the likelihood of sewage back-up into the dwelling and surfacing sewage. Many cesspools and seepage pits were intentionally sited with the bottom of the pit in groundwater, as the natural water movement carried the sewage away. Raw or partially treated sewage should never reach groundwater, as the impacts to an aquifer are similar to the damages in a ditch, stream, or lake. There have been numerous studies documenting contamination of ground and surface water from wastewater systems in contact with groundwater (Allen and Morrison, 1973; Anan'ev and Demin, 1971; Crane and Moore, 1983; Kligler, 1921; Vaisman, 1964).

Do I have system with a cesspool or a system with a seepage pit, drywell or leaching pit?

Diagram of a cesspool discharging raw sewage into the environment
A cesspool discharges raw sewage into the environment
Diagram of a seepage pit discharging partially treated septic tank effluent into the environment
A seepage pit discharges partially treated septic tank effluent into the environment

A cesspool is an underground tank with holes in the side and/or bottom through which wastewater is discharged. The wastewater seeps into the surrounding soil through the bottom and openings in the side of the pit. Some designs may have a septic tank prior to the leaky tank and if so, it is considered a seepage pit, drywell or leaching pit.

When and how do we fix noncompliant seepage pits and cesspools?

In Minnesota, noncompliant seepage pits and cesspools must be replaced with a compliant system. The time period for upgrade is based on local public health and environmental priorities and varies from location to location. Be sure to check with your local governmental unit (LGU). A list of MN LGUs can be found under "SSTS Local Units of Government" at:

The noncompliant cesspool or seepage pit must be properly abandoned to eliminate the safety hazard and impact to public health and the environment. A licensed designer must be hired to evaluate site and soil conditions to determine the proper replacement ISTS to treat and disperse the wastewater at the site. This design is reviewed by a LGU to ensure it meets Minnesota Rules, Chapter 7080 and any additional LGU requirements. A list of licensed septic professionals can be found by contacting your LGU or under "SSTS Business Licensing, Individual Certification, and Enforcement" at:

Referenced research

Allen, M.J. and S.M. Morrison. 1973. "Bacterial movement through fractured bedrock." Ground Water 11 (2): 6-10. 

Anan'ev, N.I. and N.D. Demin. 1971. "On the spread of pollutants in subsurface waters." Hygiene and Sanitation 36 (8):292-294. 

Crane, S.R. and J.A. Moore. 1984. "Bacterial pollution of groundwater: A review." Water, Air, and Soil Pollution. 22 (1): 67-83.

Kligler, I.J .1921. "Investigation on soil pollution and the relation of the various types of privies to the spread of intestinal infections." p. 1- 75 in ( ed.) Monograph of the Rockefeller Institute for Medical Research. Vol. No.15 .The Rockefeller Institute for Medical Research, New York. 

Vaisman, Y .I. 1964. Hygiene and Sanitation. 29:21.