What a drainage field does
It's as important
as the tank itself
A drainage field — sometimes called a soakaway — is the network of perforated pipes buried in the ground that receives the liquid from your septic tank and allows it to drain slowly into the surrounding soil. The soil provides the final stage of treatment before the water re-enters the ground naturally.
Get the drainage field wrong and the whole system fails. Too small and it saturates and backs up. In the wrong location and it contaminates groundwater or sits too close to a watercourse. Built without reference to the actual percolation test results and it won't match what the ground can handle.
We design every drainage field from the percolation test results upwards — the correct size for your soil, your system flow rate, and the available space on your land. No guesswork, no generic templates.
Why it matters
Three ways a drainage
field can fail
Undersized for the ground
A field sized without a proper percolation test will be too small for the actual drainage rate of the soil. It saturates, effluent backs up into the tank, and the system fails. This is the most common avoidable failure we see.
Wrong location on the site
BS 6297 sets minimum distances from buildings, boundaries, watercourses, and water supplies. A field in the wrong position can cause pollution, create compliance problems, or invalidate the installation entirely.
Saturated or damaged field
An existing field that's been overloaded — through an undersized tank or years without emptying — may be beyond recovery. We assess the existing field honestly and tell you whether it can be reused or needs replacing.
What's included
Design, installation,
sign-off
Whether it's a new field alongside a new tank, or a standalone replacement for a failed one — we handle the whole job.
01
Percolation test & results analysis
If testing hasn't been done, we carry it out first. The field is sized directly from the Vp value — no estimates
02
Field design to BS 6297
Pipe length, trench depth, distribution arrangement, and siting — all calculated to the standard required by Building Control and the Environment Agency.
03
Excavation & installation
Trenches cut to the correct depth, filter gravel placed, perforated pipes laid, inspection chambers installed. Site left clean.
04
Building Control sign-off
All documentation provided. We manage the Part H process to completion — you receive your certificate.
Worth knowing
A drainage field should never be driven over or built on. We'll advise on the protection zone around the field as part of the handover so it's not accidentally damaged later.
Drainage fields should be rested periodically — some installations use a twin-field arrangement with alternating use. We'll advise whether this is appropriate for your property.
Sometimes only the drainage field has failed, not the tank. A field replacement alone can be significantly cheaper than a full system
replacement. We'll tell you honestly which applies.
Keep fats, oils, bleach, and non-biodegradable materials out of the drainage system. They kill the soil bacteria that provide the final treatment stage and shorten the life of any field significantly.