In-Ground Soil Absorption Areas

  • The soil absorption area receives the liquid effluent from the septic tanks and distributes it over a specific area.
  • Equal distribution of the effluent is very important to the proper functioning of the system.
    • In a gravity system, this is achieved by a distribution box
    • In a pump system, this is achieved by pumping the effluent through laterals.  These laterals should be accessible through lateral risers.
  • The effluent then filters through the soil under the pipes and is treated chemically and bacterially by the components of the soil.
  • The size of the soil absorption area is based on the size of the house and the percolation rate of the soil.
  • State law requires that there be at least four feet of usable soil for the effluent to percolate through before it reaches the water table.
  • The type of system installed will depend on the slope of the property, the depth of usable soil, and the percolation rate.

Types of Conventional Soil Absorption Areas

  • An inground seepage bed
  1. For seepage beds, the entire absorption area is excavated and lined with crushed stone.
  2. The pipes (laterals) are then placed over the stone and the entire bed area serves as an absorption area for the effluent.
  3. Leaching chambers may be used in place of gravel.
  • A set of trenches
    1. A standard trench absorption area consists of two or more excavated trenches in which perforated pipes or laterals distribute effluent into a layer of crushed stone under the pipes.
    2. The effluent is then absorbed into the soil where it is renovated.
  • Elevated sand mound
    1. The elevated sand mound system is used in areas with reduced permeability, shallow soils, and poor drainage characteristics.
    2. Soils in these areas require the addition of sand above the ground to provide for adequate renovation of the sewage prior to reaching the water table.
    3. The absorption area is constructed similarly to a standard seepage bed or trench, except that the system is required to use pressure distribution and a layer of sand must be placed between the crushed stone and the natural soil cover.
    4. A soil berm is placed around the mound to protect it and to provide a suitable base for the establishment of a vegetative cover.

Types of Non-Conventional Soil Absorption Areas

  • At-Grade bed
    1. An at-grade bed is similar to an elevated sand mound, but without the sand. 
  • Drip Irrigation System
    1. Drip irrigation systems distribute the treated effluent into the soil using drip tubing that is installed just below the ground surface.