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Although most city and suburban homes are hooked up to sewers, many homes in small towns and remote areas rely on septic tanks for on-site treatment of waste water. In fact, according to the National Onsite Wastewater Recycling Association (NOWRA), nearly one third of the U.S. population is served by septic tanks. If you are among these home owners, you're probably aware that a septic tank-though out of sight and out of mind most of the time-can be temperamental. When it isn't working properly, it usually lets you know.
A septic system is a self-contained water recycling system. Located underground in the yard, a watertight tank receives and stores wastes from the house. Bacteria in the tank decomposes the wastes; sludge settles in the tank and effluent flows into the ground through a drain system. It eventually filters back down to groundwater sources.
More than one trillion gallons of wastes flow through septic systems each year. Considering that volume, it's critically important to the environment and to public health that tanks operate correctly. Improper tanks can pollute groundwater and surface water with dangerous bacteria. In developing countries, this type of contamination is responsible for outbreaks of disease, including hepatitis A, typhoid, and gastrointestinal illness.
A septic system consists of a waste pipe that is connected to the house's drain-waste-vent system, a watertight septic tank, and a drainfield (or "leachfield") or other subsurface infiltration field such as a seepage pit or a leaching chamber. Codes dictate the minimum distance a tank and drainfield may be located from the house or a well, and the size and makeup of the tank and drainfield.
To prevent overloading the septic tank and drainfield, runoff from the roof and foundation drains and other "clear" water is usually routed to a separate drain or seepage pit. Where codes permit, it's a good idea to route water from washing machines to such a pit, too.
A biological machine
The septic tank separates and processes wastes. From the waste water that flows into the tank, heavy solids settle to the bottom, forming a layer of sludge. Greases, oils and lighter solids rise to the top, creating a layer of scum. The area between these two layers is filled with liquid effluent that can flow through the outlet pipe to the drainfield system.
Inside the tank, anaerobic and facultative micro-organisms feed on the solids in the sludge and scum, breaking down their volume. This process creates gases-carbon dioxide, hydrogen sulfide and others-that exit through the vent stack at the roof. Because only a portion of the sludge and scum are broken down (about 40 percent), a septic tank must be pumped periodically. Otherwise, accumulated solids fill the tank and are forced out into the drainfield where they clog the soil's ability to percolate. A tank is usually sized according to the number of bedrooms and will typically store solids for from three to 12 years.
The septic tank should be watertight, built so that ground water cannnot leak into the tank and septage cannot leak out. As Les Eldredge, President of NOWRA, points out, "If you have water intrusion coming into the septic tank from ground water, it will raise the dissolved oxygen level in the tank, which will inhibit the biological treatment in the septic tank. This will lead to an early failure of the drainfield."
The drainfield
It's the job of the drainfield to disperse the effluent. Many drain systems have a series of trenches that branch out from a distribution box. Some have a single, larger bed, a seepage pit, or a similar means of distributing tainted water back into the ground (the right one for your home depends on local codes, conditions and practices).
The type and layout of the drainfield is designed according to the absorption qualities of the soil. To gather information on how readily the soil will absorb water, a soils engineer or septic contractor conducts "perk" (percolation) tests by digging holes in several places in the yard and filling them with water.
A conventional gravel-and-pipe drainfield begins with a level-bottom trench located from 1 to 3 feet beneath the ground, but at least two feet above the groundwater table. A perforated drain pipe is centered along the trench over 6 to 12 inches of gravel, then covered with a few more inches of gravel. A silt barrier-a synthetic fabric-covers the gravel and pipe to help keep out silt and soil, then the trench is backfilled with soil. Once effluent reaches the drain system, the gravel and soil act as a natural filter to strain and remove harmful bacteria, viruses, and other toxins so the water is clean by the time it reaches groundwater resources.
A newer type of drainfield system, made by Infiltrator Systems, utilizes a series of lightweight plastic chambers instead of pipe and gravel; these are easy to use and treat more water with greater efficiency. A 3-foot-wide trench is dug, then the 3-foot by 6 1/4-foot ribbed sections are fitted together along the trench. A special end plate is added to the end of each run, the inlet pipe is inserted and the trench is backfilled.
Septic tank care
It pays to take care of your septic tank. When maintained improperly, the necessary bacteria in the system can be destroyed, causing the biological machine to shut down. Then, sludge builds up and is pushed into the drainfield where it clogs up the system. Before you know it, you have a sewage backup and a major headache. The tank can be pumped out but the drainfield cannot. After several tank pumpings on a too-frequent basis, you may discover that you have to install a new septic system at the cost of several thousand dollars. With proper care, a system should last more than 20 years.
It's important to know where your tank is located, both so it may be inspected and pumped, and so that you can avoid driving over the tank or leachfield with heavy equipment or doing other work that might damage the system. If you don't know where it is, you may be able to obtain records from your town or city hall. Otherwise, you can hire a septic contractor, who may find it with an electronic detector or by probing the soil with a long metal rod. Once you've located it, make a map that shows its location and put the map where you'll be able to find it in the future. It also helps to mark the tank's location with a stake or stone that isn't likely to be moved.
Have your tank inspected by a septic tank professional every three to five years-more frequently if your family uses a lot of water and/or a garbage disposer. You can reduce the strain on your septic system by using less water and staggering showers, clothes washing, bathing and other heavy usage.
Be aware that what you flush or wash down the drain can damage the system. Don't flush dyed or heavy toilet tissue or paper towels, feminine hygiene products, condoms or disposable diapers. Though some disinfectants, ammonia, and cleaners are not likely to significantly damage a system, avoid washing quantities of chemicals-particularly chlorine bleach-into the system. Never pour chemical drain cleaners, solvents, such as paint, motor oil, pesticides, poisons or chemicals into drain pipes. Minimize use of a garbage disposer and don't dispose of fat, grease, or coffee grounds.
Many commercial septic treatments meant to be flushed into the system are ineffective or actually damage the system. They can promote the flow of sludge into drain lines, clogging the drainfield. Before using such a product, check with your health department to see whether the product has received state approval. Periodic inspection and pumping of your septic system are the best way to make sure it operates faithfully for many years.
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