Summary: Learn how to constructing a soak away and the regulations when building a soak away.
* This project is for a soak away used to drain surface water NOT sewage effluent (see Soak away for sewage effluent).
It consists of a hole dug into the ground and filled with rubble or coarse stone with a drainage pipe or French drain running into it. The soil in which the soak away is placed must be granular with good drainage properties, as clay soils will not allow the necessary infiltration.
Here are a few regulations and useful tips relating to soak aways.
- For obvious reasons, the pit should be in a spot lower than the area being drained.
- A soak away should also be sited so that it will not saturate the foundations of any structure.
- The soak away needs to be permanently above the water table for effective filtration. If this is not the case, the excess water has nowhere to permeate.
- If using a pipe to carry the water to the soak away, it should be no less than 75mm (3in) in diameter, although a diameter of 100mm (4in) is the ideal size.
- A soak away should not be too close to other infiltration devices, otherwise the capacity of those devices, and the ground itself, will be impaired.
- It is also a good idea to position the soak away so that there is no risk of contamination from pollutants.
Constructing a soak away
- Start by digging a pit approximately 1.2m x 1.2m x 1.2m (4ft x 4ft x 4ft). If you hit a layer of clay before reaching the required depth, simply make the soak away longer to make up for the lack of depth.
- Break up the earth at the base of the pit with a garden fork.
- Fill the hole up to about 100mm (4in) of the top with rubble. Use coarser rubble at the bottom and smaller stones at the top.
- The rubble pit then needs to be covered with a sheet of durable polythene.
- Then cover to polythene with a 75mm (3in) thick layer of general mix concrete: 1 cement with 2 sharp sand or 1 cement with 3 coarse aggregate.
- When the concrete has gone off the top of the soak away can be covered with either turf or soil to conceal.
- Garden fork
- Industrial polythene sheeting
- Sharp sand OR coarse aggregate