Percolation Testing

At Ground Consultants Limited, we offer both Soakaway tests and Percolation tests, but what’s the difference?

Soakaway Tests – BRE365

“Soakaway Tests” are typically completed in-line with the guidelines outlined in the Building Research Establishment document BRE 365. This document sets out the principles of soakaway design, and also the approved method for testing the infiltration rate of the ground.

Soakaway tests will measure the soil infiltration rate for surface water, i.e. water-run off from roofs and pavement etc.

Trial pits are excavated to depths of 1.50m to 2.50m below ground level, and are typically 0.50m wide x 1.5m long. The pits are rapidly filled with water (at GCL we use an agricultural bowser as shown in the photo below) and measurements are taken as the water drains away. In accordance with BRE 365, 3 tests should be completed within each trial pit, though it is commonplace to complete as many as are feasible within 1 day on site.

Percolation Tests – BS6297

Percolation tests are completed to assess the permeability of the ground for foul drainage.

The test procedure is set-out in BS6297, and involves excavating a much wider and shallower pit, typically using a grading bucket. A 0.30m x 0.30m x 0.30m “cube” is then excavated at the base of the excavation, and subsequently filled with water. Measurements are taken as the water drains away, and a “Vp” value is generated.

Drainage field disposal should only be used when percolation tests indicate average values of Vp between 15 and 100 and the preliminary assessment of the trial hole tests has been favourable.

Less water is used during a percolation test, meaning a standard garden tap can be used, rather than an agricultural bowser.

Ground Consultants Limited have a wealth of experience in both types of test, and use local trusted plant hire companies. To see how we can help with your project, please get in touch!