What is a Percolation Test
- A percolation test (or ‘perc test’) is an essential step when installing or replacing a soakaway or drainage field.
- It measures how quickly the soil absorbs water by recording the time it takes for a set amount of water to drain from a prepared, saturated test hole.
- The results indicate the ground’s drainage capacity and help identify the best location for the new drainage field.
We will then recommend a suitable-sized wastewater treatment system in accordance with EPA guidelines.
What Does a Percolation Test Involve?
A percolation test is carried out in several stages to ensure accurate results:
- Site Preparation – The proposed soakaway or drainage field area is identified and cleared of debris or vegetation. To avoid inaccurate readings, the test should not be carried out during heavy rain, frost, snow, or drought.
- Digging Test Holes – Several test holes are dug in the chosen area, typically 300mm–700mm deep and around 300mm square. The number of holes depends on the size of the drainage field.
- Soaking the Holes – Each hole is filled with water to fully saturate the surrounding soil, ensuring reliable test conditions.
- Drainage Testing – Once saturated, the holes are refilled with a set amount of water. The time taken for the water to drain away is recorded, usually repeating the process at least twice for accuracy.
- Calculating Percolation Rate – The percolation rate is calculated by dividing the water volume by the drainage time, expressed in minutes per inch or per centimetre.
- Interpreting the Results – These results determine the size and design of the soakaway or drainage field.
- Faster drainage rates = soil can handle higher water volumes.
- Slower drainage rates = may require a larger drainage field or an alternative system.
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