Liquefied sewage needs to percolate through 36" of dry soil colonized with aerobic bacteria to become clean ground water. When you consider that most leach field pipes are buried 18" from the surface of the ground, the installation site must be dry to a depth of 54". If ground water present within this 54", especially if it is covering the leach field pipes, no oxygen can enter the ground causing the aerobic bacteria die and the liquefied sewage will not be sanitized.
There have been cases in the township where landowners have sited a home, and some even broken ground, only to later find out that their land will not support a leach field. Since the size and location of a leach field is often decided, and must always be approved by the Franklin County Board of Health, it is a good idea to have an inspector do a site survey and soils evaluation before buying land, adding bedrooms or repairing an existing leach field.
An inspector evaluates the soil by boring holes at several locations on the lot and examining the soil in these holes. The location of high water tables, poor draining soils and any surface water, such as creeks or a lake and underground water supplies, such as a well or spring, must be identified. Discharge from roof gutters, sump pump and any natural ground surface drainage patterns must also be taken into consideration. An inspector will recommend and/or approve a leach field only if will not pose a contamination threat, can be sure that it will not become saturated by surface or ground water.
Typically, a leach filed consists of a series of pipes, often buried 18" deep on a bed of gravel and in parallel with each other. The pipes are connected together at least on one end. Liquefied sewage is gravity fed from the septic tank, through the distribution box into one end of each pipe. On newer construction, the opposite end is tied together and vented above ground level. A properly working leach field will dispose of house hold waste water by flowing the liquefied sewage through a series of small weep holes into dry subsoil. As the liquefied sewage drains away from the pipe, it if filtered by the subsoil and becomes ground water. Leach field are sized using the formula of 500' of pipe for each bedroom in the home. Many of the newer installation have a drain around the outside of the leach field area to carry off excess ground water. The concept behind this "Curtain Drain" is to remove enough natural ground water table enough to allow the liquefied sewage to leach through the necessary 36" of subsoil. These drains, often required in the township by the Board of Health, must be connected to a working drain tile system. If ground water builds up under a leach field, the dark liquefied sewage will float to the top and cause a foul odor. Sometimes referred to as a "Glazed" leach field, this is not only common with older leach fields but is also considered a dangerous failure that must be repaired.
A septic tank functions as a holding tank of sewage and can range in size from 500 to 3,000 gallons, depending on the number of bedrooms. A working septic tank will allow only liquid will pass to the leach field so as not to clog the small weep holes and the subsoil with suspended solids. Septic tanks perform this function through separation and microbial digestion.
A Simplified View of a Septic Tank
In the septic tank, the denser solids sink to the bottom as sludge and the lighter solids, such as grease and oil, rise to the top and form a scum layer. The space in between should be all liquid. Using a series of baffles, the scum layer is held back at the top and the solids are pooled at the bottom. Only liquid can flow under the baffles to the outlet pipe. This is called separation.
The sludge is liquefied by natural enzymes and anaerobic bacteria (does not need oxygen). This process is called microbial digestion and is the exact same process used on a much larger scale at many municipal waste water treatment plants throughout the country. All liquefied sewage flows out of the septic tank into the leach field.
The liquefied sewage in the septic tank flows by gravity to a small buried box called a distribution box. On many newer systems, this box allows the homeowner to control which section of leach field pipes are used in the leach field. The idea is that, by periodically changing where the liquefied sewage is drained, one part of the leach field can dry up while the other part is carrying the load. In any case, the distribution box evenly distributes the liquefied sewage from the septic tank to the leach field in an even and consistent manor.
The septic tank also acts as a holding tank for waste that can not be liquefied such as cooking fats and greases, proteins, starches, vegetable peelings, prophylactics and toilet paper. This accumulated non-biodegradable matter needs to be manually removed from the tank before they overtake the liquid space and begin to flow into the leach field. Neglect of this removal would eventually result in the blockage of the leach pipe weep holes and can often result in unpleasant sewage backups into the home. As a matter of practice, septic tanks should be pumped every three to five years. The cost ranges from $200 to $400, depending on the tank's size and location, but is considerably less than the $5,000 to $10,000 to fix a clogged leach field and the heart ach in dealing with an overflowing toilet.
How often should you have your septic tank pumped?
(table below show number of years)
The liquids in a septic tank can turn over about 50 to 75 times a year, depending on use. This means that the bacteria and enzymes are subject to being flushed out into the leach field, not an entirely bad thing as they continue to liquefy suspended solids in the leach field pipes and subsoil, keeping the leach field open. Since bacteria grows best in a non acidic environment, it is thought that household baking soda can raise the pH and thereby help speed the natural replenishment of bacteria in the septic tank. There are also many commercial products that claim to replace the enzymes and anaerobic bacteria but their claims can be overstated and the products expensive. Additives to septic systems should only be considered after consulting with a professional.
Living with a Septic System
Prolonged heavy use of water in the home for laundry and bathing often force water through a septic tank before the suspended solids can separate. Also, the use of today's soaps, detergents and cleaning agents can kill off the natural enzymes and bacteria that liquefy solids. Allow your septic tank a period of rest during the day after very heavy or prolonged use. Also, consider using biodegradable cleaning products and non-color, non-printed toilet paper.
Never drive or park vehicles or place other large objects on the leach field area, as this will compact the soil and reduce its ability to treat liquefied sewage. It also may damage the network of pipes within the field, causing them to need to be replaced.
Avoid planting water-loving shrubs with deep root systems or trees near the leach field area, as roots could damage the pipes, or they could change moisture levels within the soil causing it to be less effective.
Water discharge from sump pumps and roof drains should never flow towards or in the vicinity of a leach field, as this would keep the soil too wet, reduce its capacity to absorb the liquefied sewage and causing puddling on the surface, creating an environmental and health hazard. Never ever send sump pump or storm water into a septic tank!
Check for depressions in the leach field area where surface water might collect. The leach field should be level with the surrounding soil to discourage puddling. If the leach field is on a sloping site, surface water diversion may need to be considered.
It is helpful to draw a diagram of the septic system which shows the location of the house, the septic tank and its manholes, distribution box and the leach field(s). This diagram will make it easier for qualified professionals and service personnel to check and maintain the system. Be sure to show the location of the septic tank and leach field in relation to the house, measuring exact distances from at least two reference points (such as the corner of the house and a tree) if possible. This need only be a sketch, although the more accurate the drawing, the more helpful it will be in the future, so include measurements of distance wherever possible.