Percolation Testing in Gloucestershire

Percolation Tests provides BRE365 soakaway percolation testing and foul infiltration testing across Gloucestershire, from the Cotswolds to the Severn Vale, supporting planning applications and self-build drainage design.

Ground conditions in Gloucestershire

Gloucestershire spans two very different geological zones. The Cotswold escarpment is largely limestone-based and often percolates well, sometimes very well — occasionally too well for a standard soakaway design without careful sizing. In contrast, the Severn Vale and areas around Gloucester and Tewkesbury sit on heavier alluvial clay, which typically drains far more slowly and is prone to a higher water table, particularly near the river. This makes Gloucestershire a county where a percolation test result can vary dramatically depending on exactly which side of the county your site falls.

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 (SuDS) support for planning submissions

Coverage across Gloucestershire

We test across Gloucester, Cheltenham, Stroud, Cirencester, Tewkesbury, and throughout the Cotswolds and Forest of Dean. Available Monday to Friday.

Why get a percolation test

Given the sharp contrast between Cotswold limestone and Severn Vale clay, an accurate site-specific test is essential in Gloucestershire — assuming a “typical” result for the area is one of the most common ways self-builders end up with an undersized or unsuitable soakaway.

Planning authorities in Gloucestershire

Drainage conditions on Gloucestershire planning permissions are set by the district or unitary council, and for larger schemes the Lead Local Flood Authority is consulted on the surface water strategy. Both expect infiltration to be considered first in the SuDS hierarchy and both expect the evidence to be a BRE Digest 365 test carried out on the site, not a figure taken from a map or a neighbour’s result. The authorities we most often write reports for in Gloucestershire are:

• Gloucestershire County Council — the Lead Local Flood Authority for the six districts below (South Gloucestershire is a separate unitary authority and its own LLFA)
• Gloucester City Council
• Cheltenham Borough Council
• Tewkesbury Borough Council
• Stroud District Council
• Cotswold District Council — Cirencester, Tetbury, Moreton, Stow
• Forest of Dean District Council

If your decision notice asks for ‘infiltration testing in accordance with BRE 365’, ‘evidence of soakaway feasibility’ or ‘percolation test results to BS 6297’, that is what we produce, laid out so the case officer can find what they need without asking again.

Ground conditions in more detail

The escarpment is the dividing line. On the Cotswold plateau the oolitic limestone is fissured and can drain very quickly — quick enough that the concern shifts from ‘will it soak away’ to sizing and to protecting groundwater, and large parts of the Cotswold aquifer are Source Protection Zones, which the Environment Agency takes seriously. Below the scarp, the Severn Vale sits on Lias clay under alluvium, with a high water table near the river: slow results and a soakaway base that has to stay clear of groundwater, which is often the harder constraint. The Forest of Dean is different again, with Coal Measures, Old Red Sandstone and old mine workings. The Cheltenham sands and the Severn terrace gravels are the vale’s best-draining ground, and they are patchy.

Which test does your site need?

A BRE 365 test sizes a surface water soakaway — roof and driveway run-off — and is what Approved Document H3 and the SuDS hierarchy point to. A BS 6297 test sizes a foul drainage field for a septic tank or package treatment plant under Approved Document H2. They use different pits, different procedures and different calculations.

Away from the towns, Cotswold and Forest villages are often off the mains foul sewer, so a treatment plant or septic tank with a drainage field is part of the design. That field is sized from a BS 6297 test, a different procedure from the BRE 365 soakaway test with a different result — one does not discharge a condition asking for the other. Where the site needs both we test both on the same day.

What our testing in Gloucestershire shows

We have carried out more than 70 tests within a dozen miles of the Gloucestershire towns listed below since 2018. Of the sites where we recorded an outcome, roughly two in three did not achieve an infiltration rate that would support a conventional soakaway. That is not a reason to skip the test — it is the reason to do it early. A measured rate, even a poor one, is what your engineer needs to size attenuation or justify a different discharge, and it is what the authority will accept. A guessed rate is what gets a scheme sent back.

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

Get a quote

Contact us for a free, no-obligation quote for percolation or infiltration testing anywhere in Gloucestershire. Call 01902 475653 or request a quote online.

Towns and areas we cover in Gloucestershire

• Gloucester — Severn alluvium and Lias clay; groundwater is usually the constraint; 23 tests within ten miles
• Cheltenham — Cheltenham sands drain well where present, Lias clay where not; 22 tests within ten miles
• Stroud — steep valleys cut into the scarp, limestone above and clay below; 14 tests within ten miles
• Cirencester — Cotswold limestone; fast rates, groundwater protection matters; 16 tests within ten miles
• Tewkesbury — Severn and Avon floodplain clays; 22 tests within ten miles
• Forest of Dean — Coal Measures and sandstone with old workings; 24 tests within ten miles

Recent work near Gloucestershire