Septic Systems:  What are they?

A septic or subsurface sewage disposal system is the system which receives all of the wastewater from a household.  The wastewater will include the blackwater (sewage from the toilets) and the graywater (sewage from the sinks, dishwasher, bath/showers, and the washer). The system will include a septic tank, distribution box, and a leach field. 

 Each septic or subsurface sewage disposal system is design for a specific site and a specific volume of wastewater.  Each site is different and must be evaluated individually.  The evaluation will involve soil characteristics, lot size and location, estimated water usage, and some others.

 Components of a Septic System

The subsurface disposal system is the most common on-site wastewater disposal method.  Aprroximately 60% of the soils in Oklahoma are suitable for this type of disposal system.  The subsurface disposal system consists of a septic tank and an absorbtion or leach field made up of a series of shallow trenches called lateral lines.  When a subsurface disposal system is properly designed, installed and maintained, the wastewater will receive proper treatment before it enters the environment.

Septic Tank:

Wastewater flows into the septic tank where liquids separate from the solids.   The heavier solids settle to the bottom of the tank while the lighter grease and scum float on top of the tank.  The natural bacteria found in the septic tank begin to breakdown the organic material found in the wastewater. 

Only the treated (effluent) liquid found in the center of the tank flows out of the septic tank and into the absorbtion field.

Absorbtion Field:

 An absorbtion field is made up of a series of shallow trenches called lateral lines.  Lateral lines can be comprised two ways:  (1) consisting of perforated pipe surrounded on all sides by 3/4' to 1 1/2' gravel and back filled by native soil; or (2) leaching chambers that do not contain gravel.

(1)            (2)

For more information about a septic or subsurface sewage disposal system go to the fact sheets from the Department of Environmental Quality at  www.deq.state.ok.us/ECLSnew/septic.htm then click on Subsurface Sewage Treatment System. 

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