A conventional soil treatment area involves gravity distribution from the septic tank to a gravel filled trench. The main function of gravity distribution systems is to accept, store, and distribute wastewater so it can be dispersed into the soil and environment. Technologies available for gravity distribution of wastewater into soil can be divided into media filled (gravel, sand, tire chips, polystyrene, etc.) and open storage types (chamber, gravel-less pipes).
Effluent gravity flows through the septic tank and into the soil absorption area. The media-filled trench has a perforated pipe extending through the media. At least 50 % of the media is below the perforated pipe. Regulations will vary as to the depth of media below and above the pipe. The media may be covered with a geotextile fabric to prevent soil migration into the media. Native permeable soil is placed on top of the fabric and extended to the soil surface. Soil is mounded over the trench to shed rainwater. An inspection port should be located at the end of the trench which allows monitoring of the ponded level in the trench.