Disposal Field is part of the sewage system where waste water flows to after leaving the septic tank. The septic tank will treat the sewage to at least a primary standard before allowing waste water to enter the disposal field. This area allows for absorption through the soil. Adequate soil must be present to filter the waste water before this water then enters the ground water system.
When designing the disposal field two areas are created. The Primary Area is the main disposal field for the waste water system. At the same time a Reserve Area of the same size is set aside. On new construction, this Reserve Area is not utilized, but rather set aside for future use in case of a failure in the Primary Area. If a repair is needed to an existing system, many times, the most economical solution is to utilize this reserve area to extend the existing disposal field.
Several factors are taken into consideration when determining the size of the disposal areas. The amount of water anticipated is typically determined from empirical data gathered from a similar use, the type of soil encountered on the site, the slope of the ground, the depth of the usable soil, location of streams, and the type of vegetation that will be utilized.
One method for determining the suitability of the soil on the site is to perform a Percolation Test. Perc Test, is used to examining the soil on a piece of property allowing decisions to be made about the type of sewage disposal system needed. This test shows the rate at which the undisturbed soil will absorb water per unit of surface area. This Perc Test as well as other observations on the site are used to create a Soil Map. This Soil Map shows the size, shape and location of different kids of soils in relation to other features on the earth’s surface, and for septic systems, these maps indicate the potential for the soil to absorb waste water.
Disposal fields can be configured in two different ways. In a Recirculating Design of a waste water system it provides equal distribution of the effluent filtered water through out the system by connecting successive trenches on both ends and by maintaining the grade in the bottom of these trenches. In Serial Distribution, each trench is connected to the next by a closed pipe laid on the undisturbed section of ground. Using this method all effluent waste is discharged to the first trench until it is filled. Excess liquid is then carried by the relief line to the next trench, and continues in this manner until the final trench is filled.