A septic tank is a sealed underground container — generally made of reinforced concrete — that collects and processes sewage discharge from residential or commercial structures. Common sources of wastewater include toilets, showers, sinks, dishwashers, and washing machines. Septic tanks are used wherever it is not practical or cost-effective to tie into a city sewage network. As a result, most rural and remote structures use septic systems to discharge household wastewater.
(Drawing reproduced courtesy Ohio State University).
Naturally-present anaerobic bacteria attack wastewater solids, reducing them to a liquid state safe enough to discharge through a drainfield into the surrounding soil. While septic systems are simple in concept, the micro-bacterial processes are very complex. As a result, proper maintenance and common sense go a long way to ensuring an optimally performing septic system.
Since residential septic systems are designed for specific capacities (generally in the 500-1500 gallon range), exceeding the design capacity will limit the effectiveness of the organic processing. This leads to early failure, which then becomes an inconvenience to the homeowners until the problems are remedied. Generally, newer systems must be at least 1000 gallon capacity or greater. Some municipalities even require dual-container systems, which provide better decomposition of waste solids.
Since roughly half of the organic waste does not decompose naturally, periodic pumping is required every few years to keep septic tanks in peak operating condition (see Table 1). This removes any remaining organic sludge and other wastes that accumulate at the bottom of the tank.
Limiting unnecessary water flow into the system also helps. Therefore, washing machines and dishwashers used with bio-degradable detergents that produce “gray water” could be discharged separately rather than through the septic system.
Furthermore, since the organic environment inside a septic tank is susceptible to disruption, never introduce solvents, bleach, acids, or petroleum products into the system. Solids can begin to overflow into the drainfield, causing them to clog — resulting in a very expensive repair.
Expensive additives that claim to promote improved decomposition are not necessary. In fact, the larger scientific community specifically recommends against their use. Typical septic systems are full of bacteria, which if left on their own in a properly maintained environment, will promote natural decomposition. If you are injecting such additives, you may be wasting your money or, worse, hampering the natural processes at work.
Evolution of the Septic Tank In the early days when man needed some privacy and protection from the elements, he dug a hole in the ground, lined it with stone, brick, wood or other available material and built an “outhouse” style structure. Delivery of waste to its final resting place was by gravity. Once the hole filled up, the outhouse was moved to a new location. Sometimes lime or ashes were used to subdue the odors.
It wasn’t until the mid-1800’s that indoor plumbing and the toilet took root. Only in 1880 did toilet paper come into existence, courtesy of the British Perforated Paper Company. Alas, man was then able to relax in the comfort of home.
Although the outhouse evantually began to disappear, proper waste disposal remained an issue. The practical solution was to connect a pipe to the pit that once served as the outhouse. Covering the hole provided protection from accidental falls and natural odors. The pit serving the toilet became known as a cesspool.
Soon it became obvious that the cesspool couldn’t handle the extra load of household wastewater. Eventually it was discovered that by putting a watertight tank in line between the house and the cesspool, much of the waste could be removed from the flow of wastewater, trapped in the tank where it would naturally decompose. This treatment chamber became known as the septic tank. Note that the septic tank has a baffle at each end to help keep waste in the tank. The original pit remained as the part of the system that returned “clarified” wastewater to the ground. It then became known as a dry well.
Due to heavy use, poor soil conditions, age of the system or a combination of these factors, the drywell sometimes plugged up. (Wastewater still contains soaps, greases and other solids that seal the pores of all but the most porous soils.) Often a second (or third or fourth) drywell would be installed after the first to increase the soil absorption area. Note that an alert installer typically places a baffle at the outlet of the original drywell to help keep floating solids from passing into the new dry well.
Then as environmental awareness increased, it was learned that many septic systems were built too deep into the ground. There was risk of polluting drinking water by allowing wastewater to flow directly into the water table before it was properly treated by filtration through the soil. It wasn’t until 1967, for example, that the State of New Hampshire passed regulations requiring any leaching portion of a septic system (the part that sends water back into the ground) to be at least four feet above the seasonal high water table. This resulted in the switch from dry wells to leach fields, using larger “footprint” areas much shallower into the ground.
About the same time, most installers switched from the old-style steel septic tanks to the more permanent concrete type. Then as man was forced to settle on poorer ground with higher water tables, leach fields began to get pushed out of the ground to maintain separation to ground water. In many cases, pumps now have to be installed to get effluent up to these mound systems.
To save space and simplify construction of these raised systems, many new approaches have been developed including the use of plastic or concrete chambers as well as other innovations.
If you have a relatively new system that employs one of these modern innovations, chances are that you have a plan available to show you the type of system and its location.
If you have an old house with an unknown type of system, you could be anywhere on this evolutionary chart.
Using the accompanying troubleshooting tips should help you determine what type of system you have and also what is wrong with it if you are having a problem.
Locating Septic Tank
Remarkably, homeowners may not always know the location of a septic system. Older homes may have no written documentation or the former owners cannot be located. If the exact location of a septic system is unknown and the local city or county has no written records, begin looking for signs of a tank outside the house where the waste pipe exits the foundation or basement wall. Note the direction of the pipe through wall. When plumbing exits below a slab on grade, check the side of house with roof vents, especially if most of the plumbing is on that side of house. Look for a spot on the ground where snow melts first, grass turns brown or there is a slight depression or mound. Steel tanks will sometimes bounce slightly when jumped on. But be careful, steel lids rust out! Falling feet first into a septic tank is dangerous and unhealthful.
A thin steel rod with a tee handle makes a handy probe. Carefully pierce the probe into the topsoil until achieving several “hits” at the same depth. This indicates the top of the tank. A metal detector can help locate even concrete tanks and cesspool covers as they generally have steel reinforcing bars within. Another trick is to insert a snake in the house cleanout and push it until it stops. Gently sliding the snake against the inlet baffle can often send a shockwave that can be heard or felt at the ground surface by a second person. (Note that sometimes a snake can curl up within a septic tank, or particularly within a cesspool or drywell as there is no inlet baffle — making this technique useless.)
If the snake hits an obstruction but cannot be felt at the surface, remove it from the cleanout and measure its penetration into the pipe. Draw a arc on the ground at the distance of snake penetration from the house and try again with the probe along this arc. Remember that the pipe from the house may not be heading straight towards the tank.
If all else fails, locate and uncover the waste pipe where it leaves the house and again every few feet until the tank is located. Or ask a previous owner, neighbor, or septic pumper who may have serviced the system in the past.
Note: Devices are available that transmit a radio signal along a snake or from a thin ” mole” that can either be flushed or taped to the end of a snake. This signal is traced by a receiver wand as the snake is pushed through the waste pipe with uncanny accuracy.
Determine Tank Type Next, determine the type of tank:
Primary / secondary septic tank
Two or more tanks are used in some installations for better settling and detention of solids. The first tank should have fresh waste entering directly from the house. (Flush colored water or similar recognizable item down the toilet and watch it enter at inlet check point.) The second tank should have a little floating grease and scum, with some settled sludge at the bottom, Note that a septic tank always has an outlet unless it is being used as a holding tank.
Cesspool or drywell
Cesspools and drywells generally have no outlet and seldom have an inlet baffle. Liquid level could be low in a septic tank if it is rusted out (steel tank) or if center seam leaks (concrete tank). If fresh waste is present, see glossary: cesspool. If no fresh waste is present, see glossary: drywell.
Found in restaurants, inns, markets, etc.
Used if system is not gravity fed. Sometimes called a pump chamber.
Once you locate the septic tank, you may wish to have it pumped out. If water runs back into septic tank from the outlet pipe when the tank is pumped out, this is a sign that the system has failed. Possible causes include compacted soil or saturated drainfield.
Trouble- shooting Tips Check lowest fixture or drain
If the problem is septic blockage, water should back up through any drain which is below the level of the toilet when flushed. Check washing machine outlet, floor drain, bathtub, downstairs apartment, or remove cleanout plug carefully (to avoid a flood). If no backup occurs, the problem is likely with the toilet or other household plumbing only.
If the distribution box for side hill trench system is out of level, one trench may be taking all water and “failing.” Re-level pipes and block outlet to overloaded trench for several months. Or, roots could be blocking one or more pipes. Remove roots and seal joints where roots entered if possible. Note that an unlevel D box will not effect leach bed as severely, because water will find its own level through stone.
Pumps and float failures
Exercise care when handling pumps as they have 110- or 220-volt supply lines, which may not have GFIs (Ground Fault Interruptors). Some float systems (which turn pump and alarm on and off) may also contain full line voltage. Use insulating rubber gloves and follow procedures with a disinfecting hand wash for sanitation. Or call a licensed plumber if required by code.
Exercise care using snake in cleanouts or drains as some waterborne diseases can be transferred through contact. Use rubber gloves and surgical masks and follow with disinfecting wash. Stiff garden hose can sometimes be used in place of snake. Disinfect after use with chlorinated bleach and fresh water.
Usually means soil plugged due to age, overuse, underdesign, lack of maintenance, or a combination of these. Requires field replacement or rest. See: Alternating Fields.
Same reasons as above. However, drywells can sometimes be excavated around and repacked with crushed stone to create a new soil surface for absorption. Check codes.
Settling, breaking, crushing, pulling apart and backslope are installation related. Freezing, plugging at joints, corrosion or decomposition and root plugging (though also caused by poor installation) can occur later. Insulating, replacing, releveling, sealing joints, and properly backfilling will resolve most problems.
Plugging often occurs from scum buildup within baffles, roots entering through poorly sealed joints, tanks installed out-of-level or backwards, or pipes sticking into the tank too far and nearly hitting baffles, blocking waste. Correct as needed.
Locating field or drywell
Follow directions for finding a septic tank except start at the septic tank outlet rather than at the house. Snake will not hit a baffle within a drywell as there is none. It may or may not hit the side of a Distribution Box but could possibly pass through into one of the outlet pipes if pipe is in line with inlet.
Tips and Suggestions Reprinted from the National Onsite Wastewater Recycling Association (NOWRA)
Conserve water to reduce the amount of wastewater that must be treated and disposed
Repair any leaking faucets and toilets
Only discharge biodegradable wastes into system
Divert down spouts and other surface water away from your drainfield
Keep your septic tank cover accessible for tank inspections and pumping
Have your septic tank pumped regularly and checked for leaks and cracks
Call a professional when you have problems
Compost your garbage or put in trash
Use a garbage grinder
Flush sanitary napkins, tampons, disposable diapers, condoms and other non-biodegradable products into your system
Dump solvents, oils, paints, thinners, disinfectants, pesticides or poisons down the drain which can disrupt the treatment process and contaminate the groundwater
Dig in your drainfield or build anything over it
Plant anything over or drainfield except grass
Drive over your drainfield or compact the soil in any way
Example 1: Pumping frequency for a 1,000 gallon tank in a home with 4 people is at least every 3.7 years.
Example 2: Pumging frequency for 1,500 gallon tank in a home with 6 people is at least every 2.6 years.
An electromechanical device that provides audible and visual indication that the water level in a pump or holding tank is above recommended levels.
Alternating leach field
One of two or more leach fields designed to be used while the other(s) rest. They are generally fed via a manually operated diverter valve located in the line from the septic tank.
Pipe tees or partitions within a septic tank which reduce turbulence at the inlet and prevent floating grease and scum from escaping into the leaching system at the outlet. (They are usually the first part of a steel tank to rust away, leaving the leach field or drywell unprotected from excessive solids overloading.)
The original type of sewage system, often still in use in older homes. They were simply a single hole in the ground loosely blocked up with locally available materials – stone, brick, block, or railroad ties – and capped either with ties covered with a layer of old steel roofing or a cast-in-place concrete lid with a cleanout hole near the center. All household wastewater entered and the liquid portion was absorbed into the ground. When the soil plugged, a new cesspool was added. Wiser installers placed an elbow, or better still, a tee in the outlet pipe from the first cesspool, creating a baffle to hold back floating grease and scum.
In a sense, this created the first type of septic system, because the first cesspool in the line, sealed by its own demise, served as a septic tank and the subsequent tank provided a greater degree of settling and separation of soil-plugging solids and some absorption. (Owners often have the first tank pumped out to maintain system operation.)
Open-bottomed pre-cast concrete or plastic structures placed next to each other in an excavation to take the place of crushed stone in a leach field. Unlike leach fields, heavy-duty chambers can be driven over.
A removable plug in a “wye,” or a “tee” in a sewer line where a snake can be inserted to clear a blockage.
Distribution box or D-box
Usually a small square concrete box within a leach field from which all pipes lead to disperse effluent within the field. Newer boxes should be marked at the surface to protect from vehicle traffic.
Constructed identically to a cesspool and differs only in that the clarified effluent from a septic tank or the wastewater from a washing machine or other grey water may enter. Modern drywells are often pre-cast perforated rings surrounded by crushed stone to increase the absorption area. Drywells can also be used to return storm water to the ground or to relocate basement drainage water to another location above the water table.
Drywells are not commonly installed today because of laws requiring the bottom of a leaching system to be 4 feet above the seasonal high-water table.
A water supply well that is simply a hole in the ground lined with stone, brick, concrete, plastic or steel to hold its shape. The lower portion of the lining is perforated, or pierced, to let in water from the Aquifer or ground water table. The upper portion of the lining is water tight to keep surface water from entering and contaminating the well. Dug wells are often called shallow wells to differentiate them from drilled or driven wells that extend much deeper into the ground. Dug wells in our area are often a minimum of ten feet or so into the ground and a maximum of 20 to 25 feet, a practical and safe limit for machines to dig.
Shallow wells for water supply are very similar in concept to dry wells which return wastewater or rain water back to the ground. Both are designed to exchange water between the structure and the soil. The major difference is that water wells are purposely built into the ground water table and dry wells are built above the water table to keep wastewater from entering untreated.
The clearish liquid that flows out of the septic tank after the tank has “taken out the big pieces.”
Filter Fabric: Synthetic cloth-like material that is used for several different types of construction-related applications such as erosion control, road stabilization and soil separation. Can consist of either woven or non-woven fibers of varying thickness and weight. Available in 12 to 15 foot wide rolls, several hundred feet in length. Woven fabrics (usually black) resemble the modern day grain bags while non-woven fabrics can resemble a range of materials from soft felts to the stiff shiny house wrap (to which they are closely related) usually seen enveloping homes under construction.
An in-ground chamber similar to a septic tank, usually used at restaurants, markets and inns to trap grease from the kitchen wastewater before it reaches the septic tank. Unusual to find in private homes.
All liquid wastewater except for the toilet wastes (sink, shower, washer, etc.).
The part of a septic system that returns water to the ground for re-absorption. Could be a drywell, leach field, trench, chamber, etc.
A leaching system consisting of a continuous layer of crushed stone about a foot deep — usually in a rectangular layout — with perforated pipes laid level throughout to disperse effluent as evenly as possible over the entire bed.
Term often used to describe either a leach bed or leach trenches.
Built essentially like beds, except that each pipe is in its own stone-filled level trench, usually 3 feet wide. Each trench can be at a different level than the other trenches. Well suited to sloping ground.
Mound (or raised) system
A leach bed built on a mound of fine to medium-grained sand to elevate it above the seasonal high water table and/or to accommodate a system on a hillside.
A shallow, hand-dug hole saturated with water, performed as a part of a septic design to determine the soils permeability – the rate at which water is absorbed by the soil – which dictates the system size.
Pump station, pump tank: A watertight container, usually (but not always) separate from the septic tank, into which effluent flows by gravity and is then ejected by a submersible electric pump through a pressure line to the leaching system. Pump tanks often are hooked to an alarm to warn of pump failure.
Seasonal high water table
The highest elevation that groundwater reaches within the year (usually in the spring). Many states require the bottom of a leaching system to be at least 4 feet above this point.
Usually consists of a topographic survey, test pit, and percolation test plus information about the water supply and subdivision and a filing fee to the state prepared by either a licensed designer or the owner.
A watertight chamber, which all household wastewater enters for settling and anaerobic digestion of greases and solids. Original tanks were made of asphalt-coated steel. Modern tanks are made of concrete, fiberglass, or plastic. All tanks should have a set of baffles, which are critical to their operation.
Most tanks have and inspection hatch ot both the inlet and the outlet and some have a third hatch in between for pumping access. Locations of each of these should be recorded and/or marked. Steel tanks often have one round lid that covers the entire tank.
Septic tanks should be pumped every three years or so in normal operation. They should not be treated with any additives and should be protected from receiving any of the harmful chemicals used in many homes and commercial workshops. This includes disinfectants or bleaches, which can kill bacteria in the tank, and solvents, darkroom chemicals, or other materials that could pollute the water supply.
A hole dug to determine soil type, seasonal high water table, and depth to ledge. Some states require a test pit of specific depth (to determine that ledge is a minimum number of feet below bed bottom) while others require only a shallow pit to determine depth to hardpan soils.