Drainage Field Installation & Replacement
A failed drainage field is behind many problems people blame on the septic tank. Wet ground, smells and slow drains often start here. A new field is designed from ground testing and the size of the household.
- Assessment before any recommendation
- Written quote that says what's included
- Building Regulations and permits explained
- Ground put back as agreed
On this page
What it is
What a drainage field actually does
A drainage field is a network of perforated pipes laid in gravel-filled trenches below the lawn. Liquid from the septic tank or treatment plant spreads along the pipes and soaks slowly into the soil, which finishes cleaning it. It is not the same as a rainwater soakaway, and the two shouldn't be mixed.
Under the general binding rules, a septic tank must discharge to a drainage field, and new fields should meet BS 6297:2007. Soakaways installed after December 2007 can't meet the rules and need upgrading to a proper drainage field.
Signs
Signs a drainage field is failing
The usual signs are ground over the field that stays wet or mushy, unusually green strips of grass, smells in the garden, and drains that slow down or back up even after the tank has been emptied. Over time the soil around the trenches can clog, or roots and crushed pipes can block the flow.
Sometimes a field can be repaired or extended. Often the honest answer is a new field in fresh ground, which is why we test the soil first.
The process
How a drainage field is replaced
The general shape of a project. The exact method depends on your site and the system chosen.
- 1
Assess
We look at the existing system or the site, how the property is used, and what's needed.
- 2
Investigate
Ground testing where needed, access for machinery, and where the treated water can go.
- 3
Recommend and quote
A written recommendation, and a quote that says what's included and what isn't.
- 4
Approvals
Building Regulations, any environmental permit, and planning where it applies.
- 5
Install
The new system goes in. Any old system is emptied and removed or made safe.
- 6
Commission and hand over
Testing where needed, the ground put back as agreed, and the paperwork handed over.
Cost
What affects the price
We don't publish standard prices, because two jobs rarely cost the same. These are the things that move the figure.
Who it's for
Drainage Field Installation & Replacement for homes and businesses
For homes
Farmhouses, cottages, barn conversions and new rural homes. We look at how many people the system serves, the ground and the access, then explain the options in plain English.
For farms and businesses
Holiday lets, farm cottages and rural businesses often need bigger or busier systems, and volume limits matter. Farms and businesses
Planning
Planning your project
Scope
What the system serves, what's there now, and what needs to change.
Access
Room for machinery or a tanker, gateways, slopes and soft ground.
Approvals
Building Regulations, any permit, and planning where it applies.
Aftercare
Emptying, servicing and the paperwork you'll need if you sell.
Not sure which service you need?
Tell us what you've noticed. Photos of the access covers or the area around the system help if you have them, but they're optional. We'll tell you what's worth looking at first.
Questions
Drainage Field Installation & Replacement questions
Is a drainage field the same as a soakaway?
No. A soakaway takes clean rainwater. A drainage field spreads effluent from a septic tank or treatment plant through perforated pipes so the soil can treat it. They're designed differently.
Can I just empty the tank to fix a wet garden?
Emptying helps for a short time, but if the drainage field has failed the wet ground and smells come back. The field itself needs looking at.
Can a new field go in the same place?
Usually it's better in fresh ground, because the soil around an old field is often clogged. The ground test and the site layout decide.
What is a percolation test?
A test that measures how quickly water soaks into the soil at the depth of the trenches. The result sets the size of the drainage field, or shows that one won't work.
Want a clear answer for your property?
Tell us what's happening and roughly where you are. No need to know what type of system you have.