Why complete percolation tests?
Septic tanks and sewage treatment plants can discharge sewage effluent to ground via a drainage field. However, the size of the drainage field can only be established by assessing the percolation rate of the soil.
There are a wide range of different types of soil, each with different drainage characteristics. Some types of soil drain fast, some don’t drain at all. It is this ability to drain that percolation tests check.
Skipping the percolation tests means that you’re guessing whether a drainage field will drain consistently over time. If you get it wrong, you may find that your drainage field ‘backs up’ which can cause flooding of your property with sewage.
Why are infiltration tests different to percolation tests?
All properties require a means of draining water from roofs and other impermeable surfaces like paths and driveways to avoid flooding.
Many properties drain this water into the ground via soakaways. However, the size of a soakaway can only be established by assessing the infiltration rate of the soil.
However, because it doesn’t rain all the time, it isn’t necessary for a soakaway to drain all the water received during rainfall straight away. This means soakaways don’t need as big a surface area as drainage fields but they do need to be deeper to allow for storage space. Infiltration rates check the rate of drainage at a deeper level below ground than percolation tests because of this and the test needs to be different to allow for how soakaways drain away over time.
