What percolation testing is
The test that tells you what your ground can do
A percolation test measures how quickly water drains through your soil. We dig test holes, fill them with water, and time how long it takes to drain away. The results — expressed as a value called Vp — determine whether your ground will support a septic tank drainage field, how large that field needs to be, and where it should be positioned.
If the ground drains too slowly, a standard soakaway won't work and a treatment plant is needed instead. If it drains too fast, a different drainage arrangement may be required. Getting this wrong at the design stage is expensive later. A system installed without proper percolation testing is a system that may fail within a few years.
What we do on site
Three things we
assess and report on
Soil percolation rate
We dig trial holes at the proposed drainage field location, saturate the soil, and measure the drainage rate. The Vp value this produces determines system sizing under BS 6297 — the British Standard that governs drainage field design.
Soil profile & groundwater
We examine the soil layers from the surface down — type, structure, and depth to bedrock or impermeable material. We also check seasonal groundwater levels, which affect where and how deep a drainage field can be installed.
Written report & recommendation
After the test you receive a written report covering the results, drainage calculations, and our recommendation for what system you need. It's accepted by planning authorities and Building Control, and it stays with the property.
What the results mean
Three possible
outcomes
The test results determine which system is right for your property. Here's what each outcome means in plain English.
Good drainage — Vp 12 to 100
Septic tank with drainage field
Handles raw sewage from the property before it reaches the treatment system. Used where the tank or plant is uphill, or where a long rising main is needed. Sized for peak flow rates and fitted with twin pumps for reliability.
Slow drainage — Vp over 100
Treatment plant required
Your soil drains too slowly for a standard drainage field. A sewage treatment plant — producing higher-quality effluent that can discharge to a watercourse — is the right route forward.
Too fast — Vp under 12
Alternative drainage needed
Soil that drains too rapidly provides insufficient treatment as the effluent passes through. Alternative drainage arrangements are needed — we'll advise the right option for your specific site.