Percolation Tests provides BRE365 soakaway percolation testing and foul infiltration testing across Derby and the surrounding area, supporting planning applications and off-mains drainage design.
We are based in Wolverhampton, about 36 miles away, and Derby is well inside the area we cover as standard. We have carried out 9 tests within fifteen miles of Derby and 28 within twenty-five, so the ground around the town is familiar to us.
Ground conditions in Derby
Derby sits at the meeting point of several geological zones — river gravel and alluvium along the Derwent valley, sandstone to the south, and heavier marl clay further out towards the surrounding countryside. This transitional geology means percolation rates can vary considerably depending on exactly where in or around the city a site sits, so a proper on-site BRE365 test is important rather than assuming results based on a nearby postcode.
Mudstone and clay drain slowly, so sites around Derby more often return marginal or failing rates than free-draining ones. That is not automatically bad news — a measured rate, even a poor one, is what the drainage engineer needs to size the system or to justify a different approach. What causes problems is assuming a rate. River terrace gravels along the valleys can drain far better than the surrounding ground, and the only way to know which you have is to dig and time it.
What we test for
- BRE365 percolation testing for surface water soakaway design
- Foul effluent infiltration testing (Part H) for septic tanks and treatment plants
- Drainage strategy support for planning submissions
How the test is carried out
BRE Digest 365 sets out the procedure, and it is more demanding than it sounds. A single filling of a single hole proves very little.
- Trial pits are excavated at the proposed soakaway position, taken down below the level the soakaway will sit at. The number depends on the site and the design.
- Each pit is filled to at least 75% of its effective storage depth, which is where the timed measurement starts from.
- Each pit is then filled and timed three times over, measuring the fall from 75% to 25% of the effective depth.
- The slowest of those runs is carried into the calculation, which keeps the resulting design conservative.
The three fills and the draining time between them are why this cannot be rushed. A number produced quickly is a number that tends to get challenged.
Planning conditions in Derby
Applications in the Derby area are dealt with by Derby City Council, and drainage conditions are attached routinely — particularly on rural plots, barn conversions and self-builds with no mains surface water connection. The condition normally asks for infiltration testing to BRE365 and a soakaway design based on the result, approved before work starts.
Testing early is worth the trouble. If infiltration turns out not to be viable the drainage strategy has to change, and discovering that after the groundworks are priced is an expensive surprise.
Foul drainage and septic tanks
If the site is not on mains foul drainage that is a separate test. Drainage fields for septic tanks and package treatment plants are sized by the method in BS 6297, referenced by Part H of the Building Regulations, and that figure is not interchangeable with a BRE365 result. Plenty of rural sites around Derby need both, and we can do them on the same visit.
What you receive
- A full report with the recorded times for every pit and every fill
- The calculated infiltration rate, ready to hand to your engineer or planner
- Trial pit locations and depths
- Photographs of the testing on site
- A clear statement of whether a soakaway is viable, and if not, why not
Coverage
We test across Derby city centre, Allestree, Mickleover, Chaddesden, Spondon, and the surrounding villages. Available Monday to Friday.
Get a quote
Contact us for a free, no-obligation quote for percolation or infiltration testing anywhere in Derby. Call 01902 475653 or request a quote online.
Nearby areas we cover
Recent work near Derby
Percolation testing around Derby
Each dot is a site we have tested. 4 within ten miles of Derby, 25 within twenty-five.