Do I Need To Do A Percolation Test?
Who Is Asking For The Percolation Test Results
If you are reading this mt guess is that you have been asked to carry out a percolation test either by:
- You Building Inspector
- You Planning Officer
Up until about 5 years ago percolation tests were strictly the domain of building control, if they weren’t building control then they would have been carried out by a drainage engineer or a septic tank installer prior to installing a drainage field.
Percolation Testing 30cm x 30cm Hole
A building inspector might ask to see the results of your percolation testing so as to check the design of your drainage field., as might a drainage engineer if their scope does not include for obtaining the results.
What is recently new is that a planning officer may also ask for results of percolation testing. This can seam quite annoying given that it contrasts with historical requirements. However, in some cases there is a justification for doing so.
Soak-Away Testing . . . Big Hole
Why Am I Being Asked For Percolation Testing?
If you are being asked by building regs or a drainage engineer then the answer is reasonably obvious. It is to provide data (VP Rate) so you can design the drainage field at the correct size.
But why i your planning officer (or consultee) asking for percolation testing? We would suggest there are two reasons:
- Less likely – The planning officer is overstretched and doesn’t have time to determine your application, and as such they will ask for this extra detail (with no real justification for doing so ) in order to buy themselves more time.
- More likely – The planning officer is worried that after planning is granted it may become apparent that infiltration drainage is not viable on site. Lets have look as to why this might be the case:
Why Is A Drainage Field Not Viable On My Site?
Reason 1 – Lack of Space
Is there enough room on site for a drainage field? In soils were water logging is sometimes a problem like clays. The drainage field required might be very large, you don’t know how large until you have carried out the percolation tests.
Reason 2 – Clay Soils
If the VP rate is too low. Then a drainage field may not work. If you then intend to use a drainage mound, what size will it be and will this affect the layout or the appearance of the planning proposal.
Reason 3 – Very Permeable / Pervious Ground
Just as a VP rate can be too low. It can also be too high. So f you are o a site with clean sandy soils, or gravels then the permeability might be too high. This can also be a problem on ground where the has cracks in it like limestone, you might hit a fissure and all of the water drains away very quickly. Luckily this maximum rate only applies to old fashioned septic tanks, and you can get around it by using a treatment plant.
What Can Do If I Am Asked For Percolation Tests By Planning Officer?
Follow the below handy list:
- Is the request justified? If you live in the middle o nowhere with huge areas for the drainage field , and geological maps show that that you will get good drainage. . . why are you being asked.
- In all other instances just do the tests. We can do them or you, or you can find instruction on how to do them in the building regulations.
- Is the VP rate too low? Investigate a drainage mound, or perhaps investigate using a treatment plant and discharging to a river. Another option might be to run a pipe (perhaps or a long way) and connect to mains sewer.
- Is the VP Rate Too High? Swap you septic tank to a treat plant.
A very complicated solution is a borehole soak-away. his costs a lot o money and you will need to get a licence from the Environment Agency. If you thing drilling a 30m deep hole sounds difficult . . . try getting a license from the Environment Agency.
Bored Already?
Just get us to do it for you. Please contact us for a quotation.