If not properly maintained, an on-site septic system could cost you thousands of dollars to repair or replace. The following provides technical information and tips to help you avoid such an expense.
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All on-site septic systems have a septic tank, a large container that is buried underground and is made of concrete, fiberglass or polyethylene. The septic tank protects the absorption ability of the subsoil by:
Removing solids from liquid. As sewage enters the septic tank, heavy solids settle to the bottom and form sludge, which reduces the flow of sewage into the tank. While grease and other light solids rise to the surface (scum), both the sludge and scum are retained and break down while the liquid (effluent) is passed along to the drain or leach field for absorption by the soil.
Providing biological treatment. Bacterial activity breaks down the solids and liquids in anaerobic conditions (without oxygen), which are referred to as “septic,” the name given to the tank.
Retaining scum and sludge. Scum, the mat of floating solids and grease, and sludge, the solids that build up in the bottom of the tank, are eventually compacted into a fraction of its original volume. Warm geographical regions of the country allow for a more complete breakdown of the scum and sludge than cool regions. Hence, tanks in warm climates tend to not require pumping or cleaning out as frequently as tanks in cold climates. Note it is important to maintain a sufficient volume for solids to accumulate between pumpings and cleanings in order to avoid having the solids enter the drain field and clog the soil.
Septic tanks should provide at least 24-hour retention time or at least 750 gallons for a one or two-bedroom house; 900 gallons for a three-bedroom house; and 1,000 gallons for a four-bedroom house. 250 gallons should be added for each bedroom exceeding four.
Kitchen grease is generally detrimental to the septic tank’s operability. Small amounts of kitchen grease can enter the septic tank without damaging the system.
Septic Dye Test
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A somewhat useful but inconclusive test of a septic system that involves placing a tracer dye in a toilet, flushing the dye into the system, and running a test volume of water (approximately 50 gallons per bedroom) into the system to look for signs of blockage, backup or breakout of effluent. Although the septic dye test can disclose numerous septic failures, it does not find every failure condition.
US Inspect’s objective evaluation of an on-site waste treatment and disposal system’s characteristics based on the experience and expertise of a septic management professional. The SeptiCheck evaluation is designed to detect visible on-site waste treatment and disposal system deficiencies. The evaluation is based on what an on-site waste management professional is able to observe, and the professional’s knowledge and experience with on-site wastewater technology. The evaluation is intended to determine whether or not one or more of the areas identified is not functioning properly at the time of the evaluation. There can be many evidences in the tank that can identify the early stages of system failure. The SeptiCheck evaluation has the ability to identify components of on-site systems that are in the beginning stages of failures. Unlike the septic dye test, SeptiCheck includes a visual assessment of the interior of the septic tank.
Conventional Septic System
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Consists of a settling or septic tank and a soil absorption field. The traditional system accepts both greywater (wastewater from showers, sinks, and laundry) and blackwater (wastewater from toilets).
These systems are typically restricted in that the bottom invert of the absorption field should be at least 2 feet above the seasonally high water table or impermeable layer (separation distance) and the permeation rate of the soil should be between 1 and 60 minutes per inch. Also, to ensure proper operation, the tank should be pumped every 3 to 5 years. Nitrogen removal of these systems is minimal and somewhat dependent on temperature. The most common type of failure of these systems is from clogging of the absorption field, insufficient separation distance to the water table, insufficient permeation capacity of the soil, and overloading of water.
Intermittent Sand Filter
Used in conjunction with pretreatment methods such as septic tanks and soil absorption fields. An intermittent sand filter receives and treats effluent from the septic tank before it is distributed to the leaching field. The sand filter consists of a bed (open or buried) of granular material 24 to 36 inches deep. The material is usually 0.35 to 1.0 mm in diameter. The bed of granular material is underlain with graded gravel and collector drains. These systems have been shown to be effective for nitrogen removal, however, this process is dependent on temperature. Water loading recommendations for intermittent sand filters are typically between 1 and 5 gallons per day/square foot (gpd/ft2) but may be higher, depending on wastewater characteristics. Primary failure of sand filters is due to clogging, and maintenance is recommended to keep the system performing properly—resting the bed, raking the surface layer, or removing the top surface medium and replacing it with clean medium. In general, the filters should be inspected every 3 to 4 months to ensure that they are operating properly.
Intermittent sand filters are used for small commercial and institutional developments as well as individual homes. The size of the facility is limited by land availability. The filters should be buried in the ground, but they may be constructed above ground in areas of shallow bedrock or high water tables. Covered filters are required in areas with extended periods of subfreezing weather. Excessive, long-term rainfall and runoff may be detrimental to filter performance, requiring measures to divert water away from the system (USEPA, 1980).
Recirculating Sand Filter
A modified intermittent sand filter in which effluent from the filter is recirculated through the septic tank and/or the sand filter before it is discharged to the soil absorption field. The addition of the recirculation loop in the system may enhance removal effectiveness and allow media size to be increased to as much as 1.5 mm in diameter.
Buried or recirculating sand filters can achieve a very high level of treatment of septic tank effluent before discharge to surface water or soil. Dosed recycling between sand filter and septic tank or similar devices can result in significant levels of nitrification/dentrification, equivalent to between 50 and 75 percent of overall nitrogen removal, depending on the recycling ratio. Regular buried or recirculating sand filters may require as much as 1 square foot of filter per gallon of septic tank effluent.
An alternative to conventional OSDS and are used on sites where insufficient separation distance or permeation conditions exist. Mound systems are typically designed so the effluent from the septic tank is routed to a dosing tank and then pumped to a soil absorption field that is located in elevated sand fill above the natural soil surface. There is evidence suggesting that pressure dosing provides more uniform distribution of effluent throughout the absorption field and may result in better performance. A major limitation to the use of mounds is slope.
Where adequate area is available for subsurface effluent discharge, and permanent or seasonal high ground water is at least 2 feet below the surface, the elevated sand mound may be used in coastal areas. This system can treat septic tank effluent to a level that usually approaches primary drinking water standards for BOD5, suspended solids, and pathogens by the time the effluent plume passes the property line for single-family dwellings. A mound system will not normally produce significant reductions in levels of total nitrogen discharged, but should achieve high levels of nitrification.
Evapotranspiration (ET) and Evapotranspiration/Absorption (ETA) Systems
Combine the process of evaporation from the surface of a bed and transpiration from plants to dispose of wastewater. The wastewater would require some form of pretreatment such as a septic tank. An ET bed usually consists of a liner, drain field tile, and gravel and sand layers. ET and ETA systems are useful where soils are unsuitable for subsurface disposal, where the climate is favorable for evaporation, and where groundwater protection is essential. In both types of systems, distribution piping is laid in gravel, overlain by sand, and planted with suitable vegetation. Plants can transpire up to 10 times the amount of water evaporated during the daytime. For an ET system to be effective, evaporation should be equal to or greater than the total water input to the system because it requires an impermeable seal around the system. In the United States, this limits use of ET systems to the southwest. The size of the system depends on the quantity of effluent inflow, precipitation, local ET rate, and soil permeability (Otis, undated).
Aerobic Treatment Units
Can be employed on-site. These systems require regular supervision and maintenance to be effective. An aerobic bacteriological farm can digest 90% to 95% of the solid wastes that are deposited into the septic tank. Typically, oxygen is supplied to a septic system when there is a problem with pumping frequency or the overall effectiveness of the system. The typical design of these systems is such that a small compressor is located near the sewer line as it exits the house, which provides oxygen for the tank.
Chlorination, ozonation, and ultraviolet disinfection are the most common methods of disinfection in the U.S.Chlorine, the most widely used disinfectant in municipal wastewater, destroys organisms by oxidizing cellular material. Chlorine can be applied as chlorine gas, hypochlorite solutions, and other chlorine compounds in solid or liquid form.
Ozone, an unstable gas generated by an electrical discharge through dry air or pure oxygen, is another oxidizing agent. Ultraviolet radiation, generated by an electrical discharge through mercury vapor, is absorbed into the genetic material of microorganisms and hinders their ability to reproduce.
Maintenance and Life
To maximize the useful life of a septic system and prevent premature failure, all systems require proper care and periodic maintenance. King County, Washington’s Public Health Department recommends the following proper care procedures.
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Inspect your septic tank once every year and pump as necessary. Solids will eventually fill the tank and pass them into the drain field, mound or sand filter, which can lead to expensive repairs.
Avoid flushing harmful material into the septic tank. Never put grease, any kind of paper (other than toilet paper), cigarettes, coffee grounds, sanitary napkins, solvents, oils, paint, caustic chemicals or pesticides into the tank.
Additives do not improve the performance in a septic tank. They are not a substitute for routine pumping, and some can be harmful to the system or the environment.
Use water wisely. Keep the amount of wastewater entering the septic system well below the "daily designed flow," which is the maximum number of gallons the system is designed to handle per day. For a three-bedroom house, the daily designed flow in gallons per day (gpd) is 450; for a four-bedroom house, it’s 480 gpd. A septic system cannot be run at its peak capacity for very long without problems developing. Using more water than the system is designed to manage is one of the leading causes of premature septic system failure.
To reduce the risk of water overloads, use "low flow" fixtures on faucets, showerheads, and toilets (many newer homes come with low flow fixtures). Front loading washing machines use considerably less water than top load models. Do laundry throughout the week, rather than all on a single day. Promptly repair all leaky faucets and toilets.
Limit garbage disposal use. A garbage disposal can lead to a significant increase in solid build-up and waste strength problems in a septic system. Therefore, they are not recommended for use with a septic system. If your house already has one, limit the amount that it is used.
Don't construct patios, carports, decks or use landscaping plastic over the drain field or septic tank. The system should be kept accessible for proper maintenance and repair and the drain fields need oxygen in order to work properly. When soil is compacted, the drain field paved over or covered, oxygen cannot get into the soil.
Keep all vehicles off the septic tank and drain field areas. Vehicular traffic is a major cause of damage to septic systems. Septic tanks are typically not designed for vehicular traffic and may crack or collapse as a result. Drain field pipes can be easily crushed by cars being driven over them. Vehicles also compact the surrounding soil, which prevents proper drainage.
Direct water from roof drains and surface drainage away from the drain field and septic tank. Additional water from these sources may overload the drain field. Surface and ground water that enters the septic or pump tank can easily fail a system even though household water use is well within the design capacity of the system.
Don't dispose of water from hot tubs into the septic tank. arge volumes of water and residual chlorine can be extremely harmful to your septic system. Check with local jurisdictions for proper disposal of water from hot tubs.
Keep a detailed record of all maintenance activities.
Be aware of the location of all septic system components. A septic system as-built is the best source of this information. Know where the septic tank, pump tank, drain field and reserve areas are located. Protect these areas from impacts of any driveway, out building, patio, deck, swimming pool, sports court or landscaping projects.
Don’t plant trees and shrubs over septic tanks or drain fields. The water-seeking roots of these plants can damage your home septic system. Grass or shallow-rooted plants tend to be the best cover for septic systems.
Alternating Valve - PVC plastic valve device, having one inlet and two outlets, designed to be placed as a part of a conventional septic system. The valve divides the total field line footage into two equal parts. The valve is to be switched every 4 to 6 months to allow for one part of the field lines to rest while the other is used.
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Alternative Septic System - Describes the types of septic systems other than the conventional septic system. The LPP system and the Mound system are examples.
Black Corrugated Pipe - Used in conventional septic system construction. It is also commonly used for outside drainage work. Three types of black corrugated pipe are used in a conventional septic system—solid pipe (used for crossovers); perforated pipe with half-inch holes drilled in the bottom of the pipe (used in the field lines); and perforated pipe with rectangular holes around the entire circumference of the pipe (used in curtain drains).
Black Water - Refers to toilet water that carries away human waste.
Certificate of Completion - Form or paperwork that certifies that a septic system has been property installed, inspected and approved by the Health Department.
Clay - Scientific term used to describe the size of soil particles. It is more commonly used to describe soils that are composed of these tiny particles. Because the soil particles are so small and tightly packed against each other, there is little space for water to move through these types of soils. Clay soils do not perk well, and they typically cannot be used for septic system installations.
Clay Soil - Soil type primarily composed of clay-sized particles. (See Clay.)
Crossover - Solid soil pipe made of PVC or black corrugated plastic used to connect a field line trench to the next successive field line trench in a serial distribution conventional septic system. A crushed crossover pipe is one of the most common causes of septic system failure.
Curtain Drain - Trench excavated around a septic field, having a positive outlet, which collects and diverts ground water and surface water away from a disposal field. The drain is necessary where a designated septic area is subject to an excessive influx of water that may interfere with the functioning of the disposal field. If the disposal field trenches fill with ground water, and the effluent cannot perk into the soil, a failure may occur.
Cut Soils - Soils that have been mechanically altered by man. The upper portion of the natural soil has been removed, typically with a bulldozer, from the site. Cut soils are generally not suitable for septic system use, because the best part of the soil has been removed and the lower portions of the soil that are now exposed to the ground surface is clay, which does not perk.
Disposal Field - Constructed in the soil, where sewage effluent is dispersed through a series of excavated trenches (see Disposal Field Trenches), so that it will soak or perk into the soil for disposal.
Disposal Field Trenches - Trenches excavated in a predetermined and approved septic area that comprise the disposal field. The trenches are constructed in a specific manner so as to conform to Health Department regulations.
Distribution Box - Component of a conventional septic system used to equally divide and distribute effluent to the individual disposal field trenches. It is important that a distribution box not be disturbed or moved after it is in place. Any disturbance of the box may alter its ability to function properly (i.e. to equally distribute the incoming effluent) and cause a system to fail.
Effluent - Abbreviated term for Sewage Effluent.
Effluent Brake - Component of a conventional septic system used to intercept the effluent pumped to a disposal field and reduce the energy level of the pumped sewage water before it enters an alternating valve or the first disposal field trench.
Engineered System - Describes Alternative Septic Systems.
Experimental System - Type of septic system or method of sewage disposal that has not been approved for general use. This term may also refer to a property or site where a septic system (usually a Mound system) was constructed as a repair to a failing system, but the soil conditions present did not meet the minimum requirements of the regulations.
Failing Septic System - Describes the conditions that occur when a septic system is no longer functioning properly, and the sewage water from the septic tank begins to pond on the ground surface over one or more components of the system. Some factors that may cause a septic system to fail include: the age of the septic system (25 years old or older); excessive water use; damage to the disposal field area; broken pump; crushed crossover pipe; and broken tight line.
Failure - Term for Failing Septic System.
Field Lines - Term for Disposal Field Trenches.
Fill - Term for Fill Material.
Fill Material - Describes the materials—rock, soil, asphalt, concrete, construction debris, etc.—natural or man-made, deposited during filling.
Float Switch - Used to control (turn on and off) a sewage effluent pump. The switch is housed within a plastic bulb that is connected to the pump by a wire. The bulb floats at the surface of the sewage water within the pump tank, and when the water level rises to a predetermined level, the switch mechanism within the plastic bulb activates the pump. Once the water has been lowered to a predetermined level by the pump, the switch mechanism automatically turns the pump off.
Gravel - Crushed rock material used in the construction of conventional septic system field lines or LPP lateral lines. The grade or size of gravel used depends on which type of system is installed.
Gravity Flow System - Describes a conventional septic system that, due to the elevations and topography of a site, can be installed so that the force of gravity provides the power needed to move the waste water throughout the course of the system.
Gray Water - Water used in the household plumbing fixtures—sinks, bathtubs, showers, clothes and dish washing machines, etc.—other than a toilet. A common misconception is that gray water is benign and can simply be discharged onto the ground or in a creek without harm. In fact, gray water contains bacteria that is washed from our bodies and the clothes we wear, and also food wastes (i.e. kitchen sinks). Thus, gray water can create a health hazard if it is not properly disposed, either into a sewer system or a properly constructed septic system.
Installer - Person holding a current and valid license from the county to engage in the business of constructing septic systems.
Lateral Lines - Disposal field trenches of a LPP septic system.
Minutes Per Inch - Standardized unit of measurement that describes the perk rate of a soil or soil area. This term indicates that it will take “X” number of minutes for the water in a perk test hole to drop one (1) inch from an established reference point.
MPI - Abbreviation for Minutes Per Inch.
On-site Sewage Disposal - Disposing of sewage water via a septic system on the lot or land parcel on which a house or building is located. The law requires that a septic system must be on the same parcel of land that the structure occupies.
Perk - Abbreviation for Percolation. Perk refers to a soil's inherent ability to absorb water. All soil types have some degree of ability to absorb water, but not all soils absorb water at a rate that allows for the soil type to be utilized for the installation of a septic system.
Perk Area - Designated or delineated area of soil that has been subjected to a perk test.
Perk Hole - Hole dug in the ground, used to conduct a perk test. Within a perk test area, there are typically six (6) or more holes used in the performance of a perk test.
Perk Rate - Rate at which soil absorbs water. The perk rate is measured in a standardized unit of Minutes Per Inch (see Minutes Per Inch). Perk rates less than 15 MPI and greater than 105 MPI are too fast and too high, respectively, to permit the installation of a septic system.
A high soil perk rate indicates that the sewage water is not sufficiently filtered by the soil and may subsequently contaminate the groundwater under such soil areas. A low soil perk rate indicates that a septic field installed in such a soil may not be able to absorb the sewage water and a failure may result.
Perk Test - Act of conducting a perk test by an authorized inspector.
Perk Test Area - Site that has been assessed and approved for a perk test. The area is generally shown on the perk test report sheet, a separate sheet of paper attached to the perk test report sheet, or on a plat prepared by a surveyor. The area's dimensions are shown as well as distances from prominent landmark features (i.e. creeks, fence lines, property lines, trees near the area, etc.) in order to identify the exact area location.
Preliminary Soil Investigation - Process of having a soil scientist look at a property in a cursory manner in order to provide ideas as to the potential for that property with regard to its support of an installation of a septic system. The preliminary type of site investigation is commonly used by people interested in purchasing a parcel of land, generally for some type of development purposes, so they may have some knowledge as to whether or not the land has any potential to be approved for septic system installations.
Public Sewerage - System built and operated by a city or municipality to collect, treat and dispose of sewage in an environmentally safe manner.
Pump - Term for Sewage Effluent Pump.
Pump System - Describes conventional septic systems that require the use of a pump and pump tank in their construction. When the disposal field area for a conventional system is located at a higher topographic elevation than the plumbing stub out elevation, a pump arrangement (i.e. a pump tank containing a sewage effluent pump) must be added to the system setup to pump the sewage water to the disposal field.
Pump Tank - Tank that contains the sewage effluent pump. The pump tank generally sits in tandem to or adjacent to the septic tank. It receives the clarified sewage effluent from the septic tank, and when the effluent fills to a predetermined capacity within the pump tank, the pump is activated by a float switch and begins pumping the effluent to the disposal field.
PVC Pipe - Solid, rigid white plastic pipe commonly used for household plumbing. The pipe is manufactured in different thicknesses. PVC stands for Polyvinyl Chloride.
Raw Sewage - Newly created sewage that enters the septic tank.
Repair - Act of correcting a failing septic system, enlarging a septic system to accommodate a proposed addition to a house, or the relocation of a system to allow for a house addition or property improvement (i.e. the installation of swimming pool). When a septic system is failing, the repair may be as simple as having an installer replace a crushed or blocked crossover pipe, or it may involve the complete construction of a new septic system. In the case of a proposed house addition or property improvement, the repair may simply involve enlarging the size of the existing system, or it may require the construction of a new septic system on another portion of the property.
Repair Permit - Required of a property owner in order to have a septic system repaired, enlarged, or relocated. The requirements outlined on this type of permit are determined as the result of a Repair Investigation.
Reserve Area - Area of a property specifically designated, either on a septic permit or on a plat, for a future septic system installation.
Septic Field - Term for Disposal Field.
Septic Permit - Term for Septic System Permit.
Septic System Failure - Term for Failing Septic System.
Septic System Permit - Permit to construct a septic system, which is issued by the Health Department.
Septic Tank - Water-tight, pre-cast concrete receptacle that receives and holds the sewage generated through the use of water in a structure. The purpose of the septic tank is to: 1) receive the incoming sewage from the structure; 2) allow for the solid organic material portions of the sewage to settle to the bottom of the tank; and 3) allow the lighter than water material portions of the sewage (i.e. domestic oils and grease) to float to the upper surface of the water level in the tank. The process of the separation of the sewage components is called clarification. An internal arrangement of baffles in the tank allows only the clarified sewage, or sewage effluent, to flow out of the tank. The effluent then flows through a tight line either to a pump tank or directly to the disposal field.
Septic Tank Pumper - Person specifically licensed to remove and properly dispose of the contents of a domestic septic tank. The term pumper assumingly comes from the manner which is used to remove the septic tank contents. The pumping contractor has a large truck with a large, 1000 to 2000-gallon capacity, steel tank mounted on the vehicle. A powerful vacuum pump is connected to the steel tank. When the pump is activated, a sufficient suction force is generated so that the sewage contents of the septic tank can be drawn through a large diameter flexible pipe into the steel tank on the truck and thus removed for disposal.
Sewer - Term for Public Sewerage.
Sewage - Water-carried wastes discharged from a plumbing collection system from residences, buildings and commercial and industrial establishments. Since all water-carried waste is considered to be sewage, there is no distinction between gray water and black water. Thus, in a dwelling or structure served by a septic system, all wastewater must be directed to the septic tank for disposal through the septic field.
Sewage Effluent - Sewage, having been clarified by the septic tank, that flows from the outlet of the septic tank.
Sewage Effluent Pump - Electrically powered pump specifically designed by a pump manufacturer to not only pump sewage effluent, but also to endure the extremely harsh conditions that result from being submerged in the effluent. These pumps should not be confused with sump pumps, grinder pumps, or any other type of pump. Sump pumps are light duty pumps that are made to pump clear water, not sewage effluent. Grinder pumps are special purpose pumps designed to grind up and pump raw sewage from a small holding tank to a public sewer line.
Sewage Water - Term for Sewage Effluent.
Soil - Natural body of decomposed mineral and organic material, layered upon the earth's surface, which is capable of supporting plant life. Natural, undisturbed soil, having acceptable percolation capabilities, drainage properties and depth-to-bedrock or water table characteristics, must be present in order for it used for the installation of any type of septic system.
Splash Box - Device used prior to the conception of the Effluent Brake. The splash box served the same purpose as the Effluent Brake. The box is constructed of concrete and is generally about 18 inches in length, width and depth, depending on the manufacturer. The square concrete top is usually exposed at the ground surface. See Effluent Brake.
Surveyor - Person licensed to practice the profession of surveying. The services of a surveyor are required to stake lot lines and lot corners, set soil mapping grids, stake platted septic areas, and stake easements.
Switch Valve - Term for Alternating Valve.
Tight Line - Solid PVC pipe used to carry the sewage effluent from either a septic tank (in a gravity flow system) or a pump tank (in a pump system) to the disposal field.
Tract - Large parcels of land (i.e. parcels being 5 acres or larger). The term is commonly used in the phrase large acreage tract.
Well - Hole drilled into the earth for the purpose of accessing and retrieving a natural resource (e.g. water, oil, gas, etc.). The most common purpose for drilling a well is to create a source of drinking water for domestic use. When a well is drilled into the ground, the conduit created to tap into the groundwater resources of an area can also provide a direct access for the passage of surface contaminates to the groundwater resources in that area.
Zoning Certificate - Written verification that shows that the proposed use of the property is approved. The zoning certificate must be obtained before an individual applies for a septic permit.
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With so many types of septic systems out there it is easy to become confused when distinguishing between them. The most common septic system is referred to as the “traditional system.” It’s nothing fancy; just a tank, some pipes, and a leaching field.
It all starts with the septic tank, which serves several functions. Most important, it retains the solid waste. The heavy solids from the waste settle to the bottom, forming “sludge” and the oils and light solids rise to the top, forming “scum” or a “scum mat.” By separating the solids, the tank allows only the liquid in between the sludge and scum, known as effluent, to pass through to the absorption area.
The septic tank also allows naturally occurring bacteria to break down the retained solids. In a traditional system the bacteria acts without the aid of airflow (i.e. anaerobic) and only breaks down approximately 65-70% of the solids. In a system where air is introduced (i.e. an aerobic system), the breakdown rate is much higher, at approximately 90-95%. Once broken down, the solids become part of the effluent, which is passed into the absorption area.
Buried at variable depths below the ground, the tank is made of concrete, fiberglass, polyethylene, or metal (metal tanks are no longer used, but can still be found in some older systems). Some tanks are separated into two compartments, which allow more solids to settle out before the effluent leaves the tank. At either end of the tank are baffles (or sanitary tees), one is an inlet baffle and one is an outlet baffle. Last, there are two or three access holes into the tank used to inspect the baffles and pump out the tank.
Barring any problems with the tank, the water level in the tank will remain constant with the outlet baffle. As new water is introduced, it forces an equal amount of effluent through the outlet baffle into the absorption area. The baffles are “T” shaped, allowing the vertical piece of the pipe to start above and protrude well below the level of the scum. The inlet baffle slows the fast-moving incoming water from disturbing the solids in the tank. The outlet baffle prevents solids from leaving the tank before being broken down.
The Absorption Area
In a traditional system, the absorption area is a leaching field--also known as a tile bed. The leaching field is the section of the ground that absorbs effluent discharged from the septic tank. The field is comprised of several lines, or “fingers,” that stem from the distribution box, allowing the effluent to spread across all areas of the field.
Once the effluent leaves the septic tank, it enters a distribution box. The distribution box evenly distributes the effluent into each of the leaching field lines. The box must be level. If it is not, a disproportionate amount of effluent will enter one line, which will cause that part of the field to fail prematurely.
When the leaching field is initially installed, trenches are dug, a bed of gravel is laid, the lines are installed over the gravel bed, more gravel is placed over the lines, and the trenches are back-filled with soil. The gravel acts to diffuse the incoming effluent, allowing it to come into contact with more soil and absorb faster. Ultimately the absorption capacity (or percolation rate) of the soil dictates how fast the effluent will be absorbed. The “quality” of the soil varies by geographical location and will be a major factor in the design of the system (or the type of system used).