Percolation Testing

IT’S one of the most fundamental steps in the journey towards home building and its importance cannot be stressed more highly – one with potential major repercussions for you and your family’s health.

Percolation testing done correctly and by a qualified professional will let you know whether any future wastewater from your site will pose either a threat to groundwater and/or your own drinking water supply should the site drain in the catchment of your own well.

It should be noted that we are moving into about the worst time of the year to carry out percolation testing with the height of the water table reaching its annual peak over the months of March and April, typically – if your site is prone to a high water table.

That’s especially the case if your site is on heavy, boggy soil – check for rushes and reeds as an indicator for heaviness. But if you are on sandy or gravelly soil it is a good time of the year to test as the water will percolate more slowly through the bedding material.

It is very important to walk the site before you carry out a percolation test to consider where exactly you are going to situate the house and ancillary buildings and where, of course, the percolation area and septic tank are going to be.

The area of percolation should be kept about twenty metres from the house as a rule of thumb, even if the minimum requirement is in the order of 10ms. This is to ensure the wastewater system will not interfere with the foundations of the house. If you’re off the water mains, your well must be set back from the percolation area by at least 30m

Two weeks’ notice must typically be given the local council so your agent can inform the authority when the test will be carried out. It generally takes three key days – with holes dug on the first day, before they are soaked on the second day followed by testing the day after.

Three holes are dug by JCB on the day: The water table hole and two test holes. All the other holes must be dug by hand. T holes are dug to around 800mm at about the level of where the wastewater pipe enters the group, with P holes dug to a depth of half of that in shallow soils.

Engineers will factor in as much data as they can glean in compiling the percolation report thereafter, drawing on everything from GSI ground water mapping to bedrock mapping and more.

Once complete, you will be advised of the type of system you will need for the site, allowing you to finally lay out the complete vision for the percolation of the site – from its location to its relation to the rest of the features on site.