Why is a Soakaway Drainage Assessment Required?

Soakaway Drainage Assessments are requested by drainage engineers or by local water authorities to assess the drainage solution for site run-off. If rock/soils are determined to be sufficiently permeable, the solution will often be in the form of a soakaway, whereas for less permeable rock/soil, attenuation and/or a connection to a sewer may be necessary.

What’s included in a Soakaway Drainage Assessment?

Our soakaway drainage assessments are designed with reference to the most current guidance, which are the BRE Digest 365 on Soakaway Design and British Standard BS 5930: 2015+A1:2020.

Practically, soakaways involve excavation of a trial pit, which is then filled with water from a tractor-towed bowser or IBC. The rate at which the water level falls is then carefully measured, and the test repeated as many times as is practicable. From the site data, the infiltration value can then be then calculated, which gives a measure of the permeability of the site soil. Once the permeability is known, the value can be used to assess whether/ what type of soakaway would be feasible on the site, when the proposed site layout is considered.

Soakaway testing can be carried out alongside a Phase 2 Site Investigation or Geotechnical Site Investigation to save time and resources.

Our soakaway drainage reports are issued with full sets of percolation rate calculations and soil logs, as well as preliminary recommendations for soakaway design.

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