Ohio State University Extension Factsheet

Ohio State University Fact Sheet

Agricultural Engineering

590 Woody Hayes Dr., Columbus, Ohio 43210


Why Do Septic Systems Malfunction?

AEX-741-00

Karen Mancl
Professor and Extension Water Quality Specialist
Food, Agricultural and Biological Engineering

Brian Slater
Assistant Professor and Extension Soil Scientist
School of Natural Resources
The Ohio State University

These are just some of the signs that a septic system has malfunctioned. Not every sign of a malfunction is obvious. In improperly designed systems, untreated sewage can move for hundreds of feet from a home before contaminating the environment or threatening the public health. The offending property owner may not even know that a problem exists.

The purpose of a septic system is to remove pollutants from wastewater to protect the public health and the environment. Pollutants such as bacteria, viruses, and nitrate threaten the public health. Ammonia, organic matter (measured as BOD), suspended solids, and nutrients threaten streams, rivers, and lakes.

To protect public health and the environment, discharge limits are set and used to evaluate systems to make sure they stay in compliance with those standards.

For example, a discharge standard for ammonia may be set at 1 mg/l to protect aquatic life. If a septic system contributes more than 1 mg/l of ammonia to a stream or pond or discharges to a ditch, drain tile, or storm sewer that flows into a stream or pond, then the system would be out of compliance.

Systems can be out of compliance because they are malfunctioning or are failing. These two reasons differ in the actions that must be taken to bring the system back into compliance.

System Malfunctions

A system malfunction is associated with improper maintenance or operation. These problems can be fixed to bring the septic system back into compliance. With proper care, oversight, repairs, and occasional upgrades the system should work for decades to protect the public health and the environment. Malfunctioning systems were initially properly designed and installed to match the soil and other conditions on the home lot. Some reasons for a malfunction are:

Avoiding System Malfunctions

For systems that are properly designed and constructed, it is easy to avoid malfunctions. Four simple steps should be followed.

  1. Avoid excess water use. Using too much water is the single biggest reason for system malfunction. The soil under the septic system must absorb all of the water used in the home, therefore it is important to limit the amount of discharged water. It is also important to space out water use by staggering loads of laundry to one per day and timing showers throughout the day.

  2. Be careful when changing landscaping. The septic system is buried just beneath the ground surface and can be damaged if vehicles drive over or are parked on top of it. Paving over even a portion of the system can damage it, leading to a malfunction. Most importantly, be careful not to direct excess rain water to the area where the septic system is buried. Make sure downspouts and drainage off roofs and paved areas flow to other areas of the home lot.

  3. Install risers and inspection ports. Because the system is buried, it is difficult to inspect to check for problems leading to a malfunction. To facilitate quick and frequent inspection, small inspection ports should be installed at the end of each lateral line. By extending the inspection ports up to the ground surface they can be easily mowed over, while still providing easy access to check for ponding in a lateral, which is an early warning sign of a malfunction. Risers over the lid of a septic tank make it easy to inspect and pump the septic tank.

  4. Regular professional inspection. Each year a quick inspection of the lateral lines reveals possible problems. If ponding is observed, first check for excess water use or changes in drainage of rainwater on the lot. Fixing a water leak or moving a downspout may correct the problem. If not, a portion of the field may have to be rested to restore its treatment capacity. Fortunately most counties require the construction of two lateral fields with a valve to switch them, which makes resting a lateral easy at no additional cost. If this is not the case, additional lateral lines may need to be installed with a valve to allow for resting a portion of the system. Septic tanks should be checked for damage every three years and pumped when needed. See "Septic Tank Maintenance" (AEX-740) for recommended septic tank pumping frequency. This and other publications are available from local county Extension offices or at Ohio State University Extension’s web site at: http://ohioline.ag.ohio-state.edu.

System Failures

A system failure occurs when the existing system cannot be fixed to bring it back into compliance. In this difficult situation, a property owner will have to install a new system. Unfortunately, many home lots do not have an adequate site to construct a new system and the property owner has few options.

If the soil conditions are suitable and space is available, a property owner may be able to construct a mound system or a sand bioreactor with an onsite irrigation system to replace a failed septic system. For more information on mound, sand bioreactor, or irrigation systems, consult Ohio State University Extension Bulletins 813, 829, 860, and 876 for sale at local Extension offices. If available, a home may be able to connect to a sewer that carries the wastewater to a system that can treat it to protect the public health and the environment. If no other options exist, the property owner may have to rely on a holding tank to collect and pump out sewage at considerable expense to prevent a public health or environmental threat.

A property owner may have a failing septic system for one of three of the following reasons:

  1. The systems designer sited the system on unsuitable soil. For example, septic systems constructed in a wet land (hydric soils) fail to operate during the wet season of the year, resulting in groundwater contamination or surfacing sewage. Septic systems designed in soils with a shallow depth to seasonal high water table, bedrock, or a slowly permeable soil layer can contaminate the groundwater that contaminates nearby wells, ditches, and streams.

  2. The contractor made an error when installing the system. For example, an installer may place a shallow drain around a septic system constructed in wet soils. These drains carry polluted water to ditches and streams threatening public health and the environment. The property owners may not even know that their system is failing and polluting public waterways, because the problem was moved off the lot.

  3. The system may be too old and exceeded its design life. Tanks and pipes buried in the ground can be expected to last 20 to 30 years before they begin to deteriorate and require repair or replacement. The soil itself does not "wear-out," but if water use has increased over the years from when the system was first installed, the system can be overloaded. Design and construction practices have improved over the last 30 years. Systems built before the 1970s may be inadequately designed by today’s standards.

Avoiding System Failures

Most failures can be avoided at the time of construction. The soil is the most important portion of any septic system. The soil must be carefully considered and protected during and after construction. A property owner can avoid a system failure in the following three ways:

  1. Detailed soil analysis as the basis of a good design. Hire a trained soil evaluator to examine the site to make sure it has adequate soil depth and permeability to support a septic system. The soil evaluator determines the soil depth to seasonal high water table and any soil layers that restrict absorption and treatment of sewage. Soil profiles are best observed in a soil pit that will need to be excavated on the lot. The soil evaluator will supplement information gathered from the soil pit with information from auger holes and probe samples and general information from soil surveys.

  2. Construction when the soil is dry. Even the most careful and experienced contractor will have difficulty installing a system during wet weather. Be patient and make sure that the soil is dry before asking the contractor to install a septic system. Construction in wet soil can result in soil compaction and smearing that reduces the ability of the soil to absorb and treat wastewater.

  3. Do not pipe sewage to the ditch or storm sewer. Do not allow the construction of a shallow drain to carry untreated sewage to a ditch, drain tile, or storm sewer. While this practice may eliminate ponding sewage in the yard, it only moves untreated sewage to Ohio’s streams and lakes. If sewage is ponding in the yard, the site is probably not suited for a septic system, and a trained soil evaluator must evaluate the site to design a replacement system. Don’t be a polluter and damage the rural environment that all Ohioans value.


All educational programs conducted by Ohio State University Extension are available to clientele on a nondiscriminatory basis without regard to race, color, creed, religion, sexual orientation, national origin, gender, age, disability or Vietnam-era veteran status.

Keith L. Smith, Associate Vice President for Ag. Adm. and Director, OSU Extension.

TDD No. 800-589-8292 (Ohio only) or 614-292-6181



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