The Septic Tank The septic tank is a small, on-site sewage treatment and disposal system buried in the ground. The modern septic tank is a watertight box usually made of precast concrete, concrete blocks, metal, or fiberglass. When household waste material enters this box, several things occur: 1.) Organic solid material floats to the surface and forms a layer of what is commonly called "scum." Bacteria in the septic tank biologically convert this material to liquid. 2.) Inorganic or inert solid materials and the by-products of bacterial digestion sink to the bottom of the tank and form a layer commonly called "Sludge." 3.) Only fairly clear water should exist between the scum and the sludge layers. It is this clear water - and only this clear water - that should overflow into the the soil absorption area. Solid material overflowing into the soil absorption area should be avoided at all costs. It is this solids overflow that clogs soil pores and causes septic systems to fail. Two main factors cause solid material to build up enough to overflow: Bacterial deficiency and lack of sludge removal. Bacteria must be present to digest and liquify the scum. If not digested, the scum will accumulate until it overflows, clogging the soil absorption area. The sludge in the septic tank - inorganic and inert material and by products of bacterial digestion - is not biodegradable and will not decompose. If not removed, sludge will accumulate until it overflows, clogging your leachfield.

The Soil Absorption Area (Leachfield) There are three main types of systems to carry off the overflow water from the septic tank: leaching fields, filter beds, and drainage pits (also called drywells or cesspools). Leaching Fields generally consist of a network of perforated pipes laid in a gravel-lined trench. Solids clogging the pipe perforations and areas around the gravel will cause drainage to slow and eventually stop. Filter beds work on the same principle as leaching fields, with a perforated pipe running through layers of sand and crushed stone. Filter beds are wider than leaching fields, and can be constructed above or below ground. They are smaller than leaching fields and can be utilized where property is not large enough for the long trenches required for a leaching field. Solids clogging the perforated pipe or the sand will cause drainage to slow and eventually stop. Drainage pits are precast or concrete block cylinders. They have closed tops, open bottoms, and holes in the sidewalls. Some older septic systems consist of only a drainage pit or cesspool.