Soakaways - Underground Drainage Systems

The term soakaway is often incorrectly used to refer to septic tank/package plant discharges to a drainage field.

Older soakaway drains were simply holes filled with rubble and coarse stone. These allow water to percolate back into the earth. On older systems often the septic tank discharges directly into a soakaway.

  • Soakaways are only for surface water (rainwater from roofs, paved areas etc.)
  • They are a hole or structure filled with rubble or underground drainage crates
  • They are designed to allow surface water to seep away into the surrounding ground
  • Over time they become blocked and will need renewing.
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Soakaways are not suitable for connection to a Septic Tank or Sewage Treatment Plant.

The purpose of a soakaway drain is to distribute surface water into the ground as fast as possible.

Thus, they do not provide the two required features of a drainage field. They are simply underground drainage systems that provide a quick solution to excess levels of surface water.

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Drainage Fields

Are you considering a drainage field? Then your property will need percolation tests to determine how suitable the ground conditions are.

A drainage field has two principal purposes:

  • Allowing infiltration of the treated / partially treated effluent into the ground, at a controlled rate
  • To enable further biological treatment of partially treated effluent, before it reaches the groundwater level

Drainage fields provide secondary treatment to the discharge from a septic tank or sewage treatment plant. They allow biological activity to remove contaminants and impurities from the liquid that emerges.

A complete septic system is formed with a septic tank, drainage field, and the pipework. The drainage field is the final part of the process, returning waste water to ground after treatment. It allows bacteria to breed, breaking down pollutants after the larger solid elements have settled.

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Regular septic tank emptying required

Drainage fields have a limited lifespan, which is shortened if the correct emptying and maintenance of the septic tank is not followed.

If you do not empty your tank on a regular basis, the suspended solids from the tank will pass into the drainage field. Which leads to clogging of the pipes and the soil becoming contaminated, meaning the drainage field no longer works. When this happens, the septic tank drainage field system comes to the end of its life. A new drainage field must be installed.

A tell-tale sign that this is happening is when your tank fills to a level above that of the outlet pipe. This usually occurs after particularly heavy rainfall.

Percolation Tests

Percolation tests determine the length and area of the trench required to disperse the effluent.

They should be carried out at the intended location of the proposed drainage field, as soil porosity varies across a site. This test should be avoided in extreme weather conditions such as drought, frost or heavy rain.

Croft Drainage Solutions can undertake this test for you. The results will indicate if the area is suitable for a drainage field, and how large the drainage field should be. We can assist you at all stages of the process.

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