Percolation test for septic tank soakaway South Wales

Are you considering installing a septic tank on your land? New Environment Agency building regulations in Wales mean you will also need a soakaway system or drainage field. Before this can go ahead you will first need to conduct a percolation test for your septic tank soakaway.

Conducting a percolation test (aka perc test) will allow you to determine the rate at which water drains away in your soil. Dependant factors such as the type of soil will affect the outcome of the test.

You will need to dig a hole where your septic tank soakaway is going, fill it with water and measure how long it takes for the water to drain away. The Environment Agency has specific guidelines which apply in South Wales.

How can Tankology help with your percolation test?

If you are unable to undertake a percolation test yourself Tankology can do it for you. Our team of friendly professionals have conducted this vital test for a myriad of homes and businesses across South Wales.

Whether for a septic tank installation or sewage treatment plant, our expert staff will provide helpful, impartial advice every step of the way. We can even help submit the final results to the Welsh Environment Agency.


Need help getting the ball rolling?

Our friendly, impartial experts are waiting to answer your questions.


Need help getting the ball rolling?

Our friendly, impartial experts are waiting to answer your questions.

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01633 246 688  |

01633 246 688

How to conduct a percolation test for soakaway

It is fairly straight-forward for you to conduct a perc test for your septic tank soakaway yourself. In some instances this may not be possible. If that’s the case with you, get in touch and we will take care of everything.

Tools you’ll need to conduct your percolation test

Shovel, spade or digger to dig the test hole

Tape measure or ruler that is a minimum of 300mm in length

Stopwatch or timer to determine the VP Number

Something to record the results on such as notepad & pen

Bucket or hosepipe to fill the hole with water

Download our Percolation test recording document
Download document (18kb PDF)
Important: This guide assumes you have already conducted a Groundwater Source Protection Zone search and dug a Trial Site Assessment hole. Percolation tests should not be conducted in wet, drought or frosty conditions.

Conduct your own soakaway percolation test in 3 steps

  • Step 1: Digging your hole

    In the area you wish to put your septic tank Soakaway dig a square hole at least 1m x 1m. You’ll also need to dig down to a depth of at least 1m. This can be a lot of work so get in a professional if you need to dig deeper or just can’t manage things.

    Once you dig your initial hole you’ll also need to dig another hole next to it that is at least 300mm x 300mm x 300mm. You’ll use this as your test zone.

  • Step 2: Saturating the soil

    Next you’ll need to fill your test zone hole with water. The drainage hole must be filled to the top. You can then leave this overnight to soak away as per Government drainage regulations. The next day you can complete the actual perc test.

    Place a marker (you can use a tape measure of marked stick) 75mm from the top of the hole and another 75mm from the bottom. Now fill the test hole up to the brim with water and wait until it drains to the top marker.

    You’ll now need to time things with a stopwatch. When the water reaches the top marker start the timer and stop it when it reaches the bottom marker. This needs to be done 3 times in both your holes.

  • Step 3: Determining the percolation

    As a result of your soil saturation tests you will now have 6 results. Firstly, add up all the timings and divide by 6 to get your average percolation. You can then divide this average number by 150 which will give you your VP number (percolation value).

    VP is the average time it takes for the water level to drop by 1mm. Anything recorded between 12 and 100 is viewed as OK. Download our perc test recording document to jot down your test results.

Frequently asked questions

Government Environment Agency building regulations mean you need to complete a percolation test as a standard risk assessment for any septic tank soakaway. As a best practice, there’s no point installing a soakaway if the effluent doesn’t actually drain away.

Across South Wales (and the UK) there are designated supply zones for groundwater. Any septic tank soakaway cannot be installed in one of these zones. You can find out more from this Government resource.

Your per test must be conducted in the area you wish to install your soakaway or drainage field.

Yes, you can do this test yourself following the instructions provided.

Essentially, you can discharge your septic tank into a bespoke drainage field or discharge it elsewhere. You will first need to obtain a permit from the Environment Agency.

Areas we cover in South Wales:

We provide our domestic and commercial tank services to homes and businesses right across South Wales. Here are some of the areas:

  • Cardiff

  • Newport

  • Abergavenny

  • Cwmbran
  • Barry
  • Swansea
  • Bridgend
  • Brecon

  • Crickhowell
  • Monmouth

  • Brynmawr
  • Llantrisant
  • Neath
  • Ebbw Vale
  • Abertillery
  • Caerleon
  • Hay-on-Wye
  • Caldicot
  • Llanelli
  • Merthyr Tydfil
  • Pontardawe

Don’t see your area listed? Not to worry, if you’re in South Wales we’ve got you covered. Call us now on: 01633 246 688