Soakaway Test

In some cases where existing soakaways are to be incorporated in a new design or where there are concerns over the quality of the construction or the ground conditions, it may be required to undertake a test of the completed soakaway. The procedure for a typical rainwater soakaway test is given below;

• The soakaway should be inspected and its condition and any visible defects noted. Of particular interest is any sediment build up, standing water, base depth and inlet depths. These details can be used to estimate the soakaways design performance. This can be combined with any inspections completed during construction if available.
• Introduce clean water into the soakaway up to the design storage capacity level. This should be done with a known volume of water. This may not be possible if a high infiltration rate is achieved.
• The water level in the pit should be maintained by adding new water using a flow meter. This should continue until a steady infiltration rate is achieved.
• Then stop adding more water and monitor the water level in the pit until a suitable period of time has passed. This will depend on the infiltration rate and on the time available for the test.
• Finally calculate the infiltration rate achieved during the falling head period of the test and compare with the design values.

The results of the soakaway test can be used to justify an old soakaway's inclusion in a new development, or to justify remedial works being undertaken.