What is a septic tank system?

        If you are like most people, you may know very little about your septic tank system. This is understandable because there have been many myths and misconceptions surrounding septic tank systems and the way that they work. We will try to give you a better understanding of what happens to your household wastewater after it goes down the drain.

        The most common type of septic system consists of two parts. 1. The septic tank 2. The leach field. There are some more complicated systems that may include aerators, pumping stations, dosing chambers, drop boxes, a raised fill leaching system or other alternate systems

        We begin with wastewater traveling out the waste pipes and empties first into the septic tank.

        The Septic Tank is a large drum or box that is most often made from precast concrete. They can also be made of metal or plastic. The size of the tank usually depends on the number of bedrooms in the home as well as the regulations in the county where it is installed. Typically it is standard for a 3 bedroom home to have a 1250 gallon tank and a 4 bedroom home to have a 1500 gallon tank. In older homes they may be much smaller as people used to use less water than today. Older tanks consist of a single compartment while newer tanks often have two. Some larger homes can have more than one tank to accommodate for usage. 

        When household waste enters the tank, several things occur. Everything flows into the tank through the inlet baffle into the middle section of the tank. Here the bacteria that live in the tank will break down the wastes and it separates. Three layers form in the tank. Organic solids form a crusty layer on the surface. Inorganic solids form a layer of “sludge” on the bottom of the tank. The middle layer is relatively clear liquid called grey water.

        The main purpose of the septic tank is to provide a place for all of the solid wastes that leaver our house to accumulate. Here the solid wastes can be dealt with until they are pumped out of the tank. As time passes, sludge continually accumulates in the tank. As the scum and sludge layers thicken, the grey water in the middle eventually gets “squeezed out”. When solids overflow beyond the tank into the leaching system it can eventually clog the leach field. When the system is neglected and the tank is not cleaned out regularly, this can cause the solids to back up into the house.

        There are several different types of leaching systems. The purpose of the leaching system is to distribute the greywater that overflows from the septic tank into the ground. Every time water goes down a household drain, water flows into the leaching system. 

        The most common type of a leaching system is a leach field with a distribution box. Other types include raised leach beds, modified raised beds, stone area beds, drywells, and leach fields on drop boxes rather than a distribution box. When a septic system is designed for an individual home, many factors are included such as the separation distance of the home from wells, neighboring wells, water lines, ground water, bodies of water, property lines, trees, streams and other utilities. 

        A “Percolation test” shows how well the soil at the site accepts water. Different types of soil leach at different rates. This is based on the soil condition, the depth of ground water, seasonal ground water, bedrock, clay, or other barriers to drainage in the soil.

        A Leach Field consists of a series of trenches that usually stem out from a distribution box. These trenches are sometimes filled with stone with a perforated pipe running through the middle of the stone. Gravel-less leaching chambers may also be used in place of the pipe and stone leach lines. Different homes and site conditions require varying lengths of leach lines which are measured in linear feet. Again, the number of bedrooms in the home and the percolation rate of the soil are used to determine the number of feet of leach line that is necessary to clear the waste water out of the septic tank and into the soil. 

        Drywells are most often made of precast concrete. They have closed tops, open bottoms, and holes in the sidewalls. Drywells can only be installed in specific site conditions where the soil is heavily graveled or sandy and where there is no issue with bedrock or ground water. Drywells are installed in a large hole with gravel around the sides and bottom. This allows for the grey water to flow out of the drywell into the soil similar to a septic tank draining into a leach field then into the soil.