It is an often-overlooked fact that drain field soil plays a major part in the proper functioning of a septic system. Overlooked, that is, until it fails. Soil failure accounts for most of the incidents of septic system failure. The role of drain field soil is that of a fine filter, and the home to trillions of microscopic organisms that feed on organic matter in the effluent from the drain field.
Clay soils are made up of tiny particles that cling together and subsequently cling well to water. To help determine how much of your soil is clay you can simply take a handful of your soil and try to squeeze it together. Once squeezed, release your fingers and see if the soil is still in a ball. The more clay it has, the more solid and less-brittle it will appear. Although it is not unique to any one place, you can usually find an abundance of clay soil in the southeast portions of the U.S.