Historically, before local regulations were established, septic systems consisted of a tank and a pipe to the nearest waterway. Also, normally only "black water" or water from the toilet was plumbed to the septic tank and all other wastes went directly to the creek.
After pollution in local waterways started to be related to diseases such as Cholera and other water borne diseases, local governments started to create regulations ordering wastewater to be discharged into the soil for final treatment.
Today, septic systems all have the common requirement, regardless of type, all septic systems have to distribute lots of water. All water generated in the home must be either treated and discharged off of the property or distributed into the soil on the property.
Soil based septic treatment systems, commonly refered to as soil absorption systems, or onsite wastewater treatment systems, all discharge their water to the existing soil on the property. These types of systems require accurate septic design plans due to the crucial potential for failure if systems are not designed.
One primary requirement when using soil for treating wastewater effluent is to ensure unsaturated flow. This can be accomplished through innovative dose methods including at-grade or above grade pressurization, drip/micro-dosing, and timed-dosing technologies.
At-grade or above grade systems include lightly scarifying or breaking the sod layer/existing vegetation, applying gravel and sand, and using a pressurized system to distribute the water over a length of soil. These are commonly referred to as mounded leaching or bed systems.