What are the Components of a Private Septic System?

The things that are most obvious are the things seen every day - the sinks, toilets, and pipes in a normal house. What are not visible are the things that are underground; the things that are underground, and the ground itself, greatly impact how a septic system works.

The individual parts of the system are the septic tank, a distribution box, and a leach field. Bacterial action takes place in the septic tank where the end products are mainly water, gases, and undigested material, called sludge that sinks to the bottom of the tank and scum that floats to the top of the tank. The septic tank contains baffles that prevent any scum that floats to the surface and sludge that settles to the bottom from passing out of the tank. The gases that are generated vent to the atmosphere via the plumbing vent system. From the septic tank, the segregated and relatively clear liquid flows into a small distribution box where it is then metered out to several perforated pipes. These perforated pipes then deliver the liquid to a large soil surface area, called a leach field, or absorption field, for absorption. The soil also acts as a filter to remove any small amounts of solids that may be carried along with the liquid. The sludge in the bottom of the tank must be periodically pumped out and properly disposed of.

There are other kinds of systems for special situations, but the septic tank and leach field is the most widely used system in our area. The following discussion concentrates on this type of system.

SEPTIC COMPONENT LOCATION - Where are The Septic System Components Located?

The concrete, or sometimes steel, septic tank is buried in the ground, usually a minimum of 10 feet from the house. The top of the tank is usually about one foot below the soil surface so it can be periodically opened for inspection and pumping. If you do not know for sure where the tank is located, the first step is to locate where the house sewer pipe leaves the house. In a house with a basement, this is where the pipe passes through the wall. Locating the exit point may be more difficult for a house with no basement. If the pipe exit can be found, the tank normally begins about 10 feet from the house outside wall and in line with the house sewer pipe. If the soil is not frozen, you can usually find the tank by pushing a slender metal rod into the ground until it hits the buried tank. You can buy a metal rod about 1/8 inch in diameter for a few dollars at most hardware stores. Be careful when probing for the tank and avoid hammering the metal rod into the ground - you could break a sewer pipe.

The distribution box is much smaller than the septic tank and is usual found about 20 feet from the house. It too is usually only about one foot below the ground. Again, you can probe the soil carefully to locate the distribution box with a slender metal rod.

From the distribution box, several pipes direct liquid to a series of pipes in trenches called laterals. The pipes in the trenches have holes in them to allow the liquid to be evenly distributed within the trench. To keep the pipes from being blocked with soil and to provide a space for water to be stored while it is being absorbed by the soil, the pipes are laid in a bed of crushed stone. Above the stone is a soil filter (usually one or two layers of what is called untreated building paper). Above the soil filter is top soil in which grass is planted.

Equally important is WHERE THE COMPONENTS SHOULD NOT BE. If there are wells, either yours or a neighbor's, the leach field must be a minimum of 100 feet from the location of the well. In some areas, the well is not allowed to be down-slope from the leach field. If there is a stream or pond, the leach field must also be a minimum of 100 feet from the mean high water mark. Normally, no part of the system should be within 10 feet of a property line. In some areas and in unusual conditions, minimum distances may be greater than those noted here. In addition, no part of the system should be under a porch or driveway and you should not drive heavy vehicles (including automobiles) over the system lest the system be damaged.