Over 30% of Oregonians dispose of their wastewater through septic systems. Properly functioning septic systems treat sewage to prevent ground and surface water pollution. It is up to the homeowner to be informed and protect their community and environment. A failing system or an illegally installed system can jeopardize that protection and the value of the home.
Consult with a local onsite professional to make sure your system is functioning properly. You can find a professional by searching for an O2WA member by name, city, type of service and/or county.
How Septic Systems Work
A septic system consists of a septic tank between 1,000 and 2,000 gallons of liquid volume, where solids settle and decompose, and a septic drain field where liquid discharged from the tank is treated by bacteria living in the soil. These pipe connections into and out of the septic tank are generally made via a T pipe which allows liquid entry and exit without disturbing any surface scum layer. Tank designs today may incorporate multiple compartments which are separated by means of a dividing wall which has openings located about midway between the floor and roof of the tank in order to further remove solids from the liquid.
Wastewater enters the first chamber of the tank, allowing heavier solids to settle and lighter liquids and solids (such a grease and oil) to float to the surface and form a scum layer.
Wastewater flows from the tank outlet into the soil absorption system which may be a drainfield (or leach field), or seepage bed.
The remaining impurities are further broken down by bacteria in the soil, adsorbed to soil particles, or taken up by roots. The wastewater is further eliminated through percolation into the soil (eventually returning to the groundwater), evaporation to the atmosphere, and by uptake through the root system of plants and eventual transpiration.
A piping network, often laid in a stone filled trench (see weeping tile), distributes the wastewater throughout the field with multiple drainage holes in the network. The size of the leach field is proportional to the volume of wastewater and inversely proportional to the porosity of the drainage field. The entire septic system can operate by gravity alone, or where topographic considerations require, with inclusion of a lift pump. Certain septic tank designs include siphons or other methods of increasing the volume and velocity of outflow to the drainage field. This helps to load all portions of the drainage pipe more evenly and extends the drainage field life by preventing premature clogging.
Solids build up in the septic tank and have to be removed from the septic tank, or solids will make their way to the drainfield and clog the soil pores, which will lead to saturated soils and likely a drainfield replacement will be necessary.
How often the septic tank has to be emptied depends on the volume of the tank relative to the input of solids, the amount of indigestible solids and the ambient temperature (as anaerobic digestion occurs more efficiently at higher temperatures). The necessity of pumping varies greatly depending on usage, number of people using the system and system characteristics. Some systems require pumping every few years or sooner, while others may be able to go 10–20 years between pumpings. Contrary to what many believe, there is no "rule of thumb" for how often tanks should be emptied. An older system with an undersized tank that is being used by a large family will require much more frequent pumping than a new system used by only a few people. Additives
A properly designed and normally operating septic system is odor free and, besides periodic inspection and pumping of the septic tank, should last for decades with no maintenance.
A well designed and maintained concrete, fibreglass or plastic tank should last about 50 years.
- Excessive dumping of cooking oils and grease can cause the inlet drains to block. Oils and grease are often difficult to degrade and can cause odour problems and difficulties with the periodic emptying.
- Flushing non-biodegradable items such as cigarette butts and hygiene products such as sanitary napkins, tampons and cotton buds/swabs will rapidly fill or clog a septic tank; these materials should not be disposed of in this way.
- The use of garbage disposers for disposal of waste food can cause a rapid overload of the system and early failure.
- Certain chemicals may damage the working of a septic tank, especially pesticides, herbicides, materials with high concentrations of bleach or caustic soda (lye) or any other inorganic materials such as paints or solvents.
- Roots from trees and shrubbery growing above the tank or the drainfield may clog and/or rupture them.
- Playgrounds and storage buildings may cause damage to a tank and the drainage field. In addition, covering the drainage field with an impervious surface, such as a driveway or parking area, will seriously affect its efficiency and possibly damage the tank and absorption system.
- Unsupervised septic tanks may cause serious injury or death to children playing nearby.
- Excessive water entering the system will overload it and cause it to fail. Checking for plumbing leaks and practicing water conservation will help the system's operation.
- Very high rainfall, rapid snow-melt, and flooding from rivers or the sea can all prevent a drain field from operating and can cause flow to back up and stop the normal operation of the tank.
- Over time, biofilms develop on the pipes of the drainage field which can lead to blockage. Such a failure can be referred to as "biomat failure".
- Septic tanks by themselves are ineffective at removing nitrogen compounds that can potentially cause algal blooms in receiving waters; this can be remedied by using a nitrogen-reducing technology, or by simply ensuring that the leach field is properly sited to prevent direct entry of effluent into bodies of water.
- Historically at least, not all varieties of toilet paper were suitable for disposal in a septic tank as they did not deteriorate sufficiently (or, at least at some points in history, some toilet paper was specifically marked as suitable for use in septic systems and some was not).
- As mentioned above, many chemicals such as household cleaners and detergents can damage the septic system, including the bacteria involved in breaking down solid waste. However, products such as enzyme, chemical, or bacterial additives are not the solution - they can actually cause more problems, not only to your system, but to the environment as well. The best method is to stop using caustic cleaners, and to allow the natural bacteria found in waste to re-accumulate. Check your local legislation to find out what is allowed and what isn't if you insist on using additives.
- Oftentimes, septic systems backup due to non-biodegradable items — either flushed objects or hair from shower drains — that make their way through the inlet T pipe and into the septic tank which then can clog the outlet T pipe and cause the liquid to overflow. To try to avoid such a problem, installation of a filter is recommended. A filter acts as a security guard and stops unwanted items from making their way into the tank. It can be installed in either the inlet or outlet T and protects the septic system.
- Septic system cover safety is an extremely important topic and ongoing issue in the U.S. Older septic system covers were concrete, which over time can crack and corrode and should be regularly checked for guaranteed security. Metal or cast iron covers also have the ability to be unsafe. Metal and cast iron are such heavy materials that if not properly installed and/or with an incorrect bottom structure, can flip themselves like a revolving door which can be especially unsafe for children and animals. It is so important that covers should be regularly checked, preferably by a professional, who can determine whether the cover is up to code standards. It is recommended that covers be checked twice per season (such as once in the beginning of spring and once at the end of spring, once at the beginning of summer and once at the end of summer, etc.). It is also highly recommended that covers are inspected after winter in colder regions as heavy snow and ice can damage even a newer cover.
- As mentioned above, many chemicals can damage septic tanks and a good solution is to allow the natural bacteria found in waste to re-accumulate OR you can use a product that uses natural bacteria to eat the toxic waste.
Some pollutants, especially sulfates, under the anaerobic conditions of septic tanks, are reduced to hydrogen sulfide, a pungent and toxic gas. Likewise, methane, a potent greenhouse gas is another by-product. Nitrates and organic nitrogen compounds are reduced to ammonia. Because of the anaerobic conditions, fermentation processes take place, which ultimately generate carbon dioxide and methane.
The fermentation processes cause the contents of a septic tank to be anaerobic with a low redox potential, which keeps phosphate in a soluble and thus mobilized form. Because phosphate can be the limiting nutrient for plant growth in many ecosystems, the discharge from a septic tank into the environment can trigger prolific plant growth including algal blooms which can also include blooms of potentially toxic cyanobacteria.
Soil capacity to retain phosphorus is large compared with the load through a normal residential septic tank. An exception occurs when septic drain fields are located in sandy or coarser soils on property adjoining a water body. Because of limited particle surface area, these soils can become saturated with phosphate. Phosphate will progress beyond the treatment area, posing a threat of eutrophication to surface waters.
In areas with high population density, groundwater pollution levels often exceed acceptable limits. Some small towns are facing the costs of building very expensive centralized wastewater treatment systems because of this problem, owing to the high cost of extended collection systems.
To slow development, building moratoriums and limits on the subdivision of property are often imposed. Ensuring existing septic tanks are functioning properly can also be helpful for a limited time, but becomes less effective as a primary remediation strategy as population density increases.
Trees in the vicinity of a concrete septic tank have the potential to penetrate the tank as the system ages and the concrete begins to develop cracks and small leaks. Tree roots can cause serious flow problems due to plugging and blockage of drain pipes, but the trees themselves tend to grow extremely vigorously due to the continuous influx of nutrients into the septic system.