Generally speaking, there are three different types of on-site septic systems—each suitable for use in different soil and topographic conditions. Additional system components (curtain drain, capping fill, etc.) are often added to these basic system types to mitigate site specific conditions.
Standard System
A standard system relies on gravity to direct the flow of wastewater. Sewage flows from the dwelling into a septic tank. After primary treatment in the tank, the wastewater flows into gravel filled disposal trenches for final treatment and dissipation into the soil.
Pressure Dosed System
Pressure dosed systems are perhaps the “simplest” of the engineered systems. By introducing a pump system into the second compartment of the septic tank, the wastewater is pressurized to the disposal field. This pressurization provides better distribution and better treatment in the soil. In areas of limited soil depth, sand may also be added to the trenches to “pre-treat” the wastewater prior to dissipation into the soil (sand filled pressure dosed system). At times, a disposal bed (at grade bed) is more appropriate than trenches. At grade beds function on the same principle as pressure dosed systems, but are constructed on the ground surface and require less soil depth than trench systems.
Pre-treatment Systems
Sites with severe site conditions (high groundwater, very shallow soils) require a pre-treatment unit to provide additional treatment before disposal into the soil. Pre-treatment systems come in many different forms, from site built systems like mounds and sand filters to pre-fabricated units like the textile and aerobic systems. Most of these systems function in a similar manner by providing a surface matrix (either sand or a textile fabric) to support bacterial growth. This bacterial growth digests the contaminants in the wastewater.
Drip Irrigation
Drip irrigation is a newer technology that is gaining momentum as the preferred choice for the disposal of wastewater. The philosophy behind subsurface drip irrigation is wastewater recycling. By re-using the wastewater, in this case for irrigation of lawn and landscape plantings, we can help to reduce the pressure on our ground and surface water resources.
A drip irrigation disposal field (dripfield) is composed of a network of small diameter drip irrigation tubing that is buried 6 – 8 inches deep. The tubing is equipped with pores spaced about every 24 inches. Because of the shallow depth and the close spacing of the pores, the wastewater can be used to irrigate a lawn or other landscape plants. In addition, the nutrients in the wastewater act as fertilizer for the plants. For additional information on subsurface drip irrigation, see our Links page for the Geoflow website.
