The principle of a septic tank soakaway is to disperse septic or sewage effluent into the subsoil at the site. The size and length of the soakaway depend on the porosity of the sub soil material (do a percolation test), the size of the property (more specifically the number of residents it is serving), and the type of treatment system. (a septic tank or a sewage treatment plant.) Note that there is a minimum size Sewage Water System that can be installed for any house up to and including 3 bedrooms. This size should be able to handle 5 persons plus one extra person added for each extra bedroom.
Common septic tank soakaways are constructed via long trench lines filled with a clean stone and have a slotted or holed distribution pipe. These trenches can be interconnected, a simple long trench, a herringbone layout, or a large filled pit.
When planning a new soakaway, always think that any soakaway depends on the subsoil permeability. Also please remember that a foul water soakaway or drain field is not a ‘Pit filled with stones’ or 'Crates' etc as soakaways are only allowed for surface roof water.
You can carry on a porosity test in order to determine the size of the soakaway that your site requires; indeed, the lower the subsoil permeability the longer the soakaway system should be. Always check the level of the natural water table in the subsoil before setting up your new soakaway in operation. If the water table rises above the base of the soakaway then the capacity of your soakaway will be significantly reduced. High water table conditions can be solved by using an effluent pump unit which will be accommodated inside your treatment plants or added separately to the outlet side of your septic tank.
Note that a septic tank soakaway is different from a rainwater soakaway. Septic tank soakaways will disperse slow flows over a 24 hour period whereas a water soakaway will disperse high flows over a short period (heavy showers…)
There are Minimum soakaway distances of 10m from a watercourse or ditch, 50m from water abstraction points, 15m from any building, and sufficiently distant from any other soakaway, and 2 meters from a boundary.
Furthermore, the soakaway should always be downslope of groundwater sources, and no water supply pipes or underground services should be within the soakaway area, like no access roads, driveways, or paved areas. Also, the water table shouldn’t be within 1.2 meters of the bottom of the soakaway trench. Please contact us for more technical details about soakaways or percolation tests; we would be grateful to help you.