Category Archives: BRE 365

Soakaway Testing Warminster – Wiltshire

Soakaway Testing Warminster  – Wiltshire

Another day. . . another hole in the ground with water in it.

soakaway testing in wiltshire in chalk

Today we have been in sunny Wiltshire, doing some soakaway tests on a residential development site. As is obvious from the pictures above, the site is on chalk. The chalk in this instance was weather and with patience could be excavated using an. . . . excavator.

We dug the hole very closed to the location ear-marked on drawings for the actually planned crate soakaway system. The results were not too bad, as the water infiltrated at a reasonable rates.

If you require BRE 365 soakaway testing for a planning application or for design purposes we can arrange on a quick turnaround. Please contact us for a quotation.

Worked Example of Soakaway with Costings

Worked Example of Soakaway with Costings

This is a fairly inaccurate walkthrough of a soakaway design to BRE 365 and an estimation of costs for installation of the designed soak away.


Provided here is a worked example of a soakaway designed to BRE 365.

The soakaway is receiving  water from a roof of 323m2.

The site is set of sandy clay soil. With a permeability of 9X10-6 (Reference Value)

1:100 year rainfall event. With 40% climate change allowance.

Size of Soakaway is 22 m3.

Soakaway dimensions are 2 meters by 11 meters. And consists of crate type modular system.


Below costs, for crate soakaway:

  • Crates: 110 crates at £30 each. £3300
  • Digger: £500
  • Soil Disposal: 40 tons @ £10 ton. £400
  • Pipe Work: £500
  • Labour: £2000

Total cost: Approximately £7000, with VAT on top probably.

Case Study

Surface Water Drainage Reporting – Essex

Surface Water Drainage Reporting – Essex

Acting on instructions from a repeat client we have prepared a number of drainage reports and plans for a project in Thurrock , Essex.

The work included a BRE 365 Report, A Surface Water Drainage Strategy and a Detailed Drainage Plan.

Surface water drainage requirements have become more and more onerous over the last few years, and you can expect a good deal of detail to be required at planning.

We used falling head test results from borehole soak-away tests to derive a required soak-away size in accordance with BRE 365.

We were then able to work up a detailed drainage scheme, include attenuation volumes, and drainage layout, drainage details and invert / cover levels.

BRE365 Soak-Away Testing in Gloucester

BRE365 Soak-Away Testing in Gloucester

SWEL recently received a phone call from a company in Gloucester who needed a BRE 365 soak-awat report for a planning application. They happened to have a digger and a water supply on site, so we attended site on the same day to take measurements etc. and produce a report (the following day).

We also included some surface water drainage strategy in the report, and made a robust conclusion that will hopefully see that the planning related matters are satisfied.

A Large Excavator

The digger used was really rather karge for the job, we would normally use a 2.5 ton digger. But in this instance we had a 20 ton beast, with a 1.5m wide bucket. Needless to say the holes were quite large.

If you require some soak-away testing undertaking we can help out, maybe not on the same day as we did here but we will do our best.

Foul and Surface Water Drainage

BRE 365 Soak-Away Tests – Gloucestershire

BRE 365 Soak-Away Tests – Gloucestershire

SWEL were engaged to undertake BRE 365 soak-away testing at a site in Gloucestershire. The works includes site works and a full written report with design calculations and soak-away sizing calculations according to BRE 365. We include trial pit logs, photographs and extra information we feel may be of use, such as empirical strength estimates.

The site was fairly large and very hilly. Which would have made access rather difficult if it were not for pre-existing access tracks, and a disused railway line which serves as a spine road for our investigations!

There were various fallen trees etc. which had to be removed before we could start work, but our site staff normal carry a selection of cutting tools so as to get things moving as quickly as possible.

Access was Tight ion the Wooded Areas – Note Quarry Face to Rear

In the course of a very long day we managed to complete 7 trail holes, with BRE 365 soak-away testing carried out in each one.

Bedrock was quite shallow at some points across the site. The western extents of the site included a quarry and a disused railway tunnel.

Many of the Soak-Away Pits Reveled Large Limestone Cobbles.

Infiltration rates across the site were variable, reflecting the steep topography and disturbed nature of the ground. The valley bottom showed slower soak-age rates whilst the the infilled quarry showed very rapid soak-age rates, likely due to the use of a very course fill media.

The field work element of each test took between 30 mins and 2 hours, which many of the longer tests being run simultaneously.

Our water bowser was towed by an Instructor from the nearby Whitecliff 4×4 Centre, who was as skilled as he was amicable.

Surface Water Drainage Design – Newton St. Cyres, Devon, UK

Surface Water Drainage Design – Newton St. Cyres, Devon, UK

Southwest Environmental have produced drainage reports on a very rapid turnaround for a private client in Devon. 
Planning officers at Devon County Council concerned with the changes to site run-off characteristics pending an extension. 
Planning was due to be determined just a few days ahead of when Southwest Environmental were commissioned. We produced a report on a 24 hour turn around, this was then put before the concerned planning officer and the application as a whole was approved. 
Impermeable Surfaces were Removed
We later provided further details of the surface water scheme to be implemented. Including size and design of the soak away in accordance with BRE 365 and various options which might be considered under Part H of the building regulations . 

BRE 365 Soak-Away Report – Brinkworth, Chippenham

BRE 365 Soak-Away Report – Brinkworth, Chippenham

On site geology is the Oxford Clay Formation. Which is described as:
“Silicate-mudstone, grey, generally smooth to slightly silty, with sporadic beds of argillaceous limestone nodules.”
BGS Borehole 398037 which is situated to the south west of site shows considerable thicknesses of Clay, extended to the base of the borehole at 44.81 mBGL.
BGS describe the Oxford clay formation as being blocky and fissile in certain areas, so there is potential the clay in to pervious (support of flow through fissures) in certain localities.
Trial pits showed varying thicknesses of made ground resting over the Oxford Clay. 
Site works comprised of 2no. trial pits with soak away tests conducted in each on. The positioning of these pits were sited in anticipation of a fairly large soak away being required. Clay typically being assumed to have a low infiltration rate.
Holes were dug using an excavator, with care being taken to keep the side vertical. This is important so as to be able to deduce an accurate volume, and pit internal surface area. 
The location of the pits can be viewed on the location plan in Appendix 1. Dimensions of the trial pits were chosen so as to representative of the final soak-away. Trial pit dimensions can be seen on the Trial Pit Log sheets in Appendix 3.
Calculations show that based on a 1 in 10 year rainfall event, allowing for a 20% increase in rainfall events owing to climate change, that a trench or pit soak-aways could provide adequate infiltration drainage for surface water from the proposed development. Results from Trial Pit 1 are adopted as a worst case scenario.
Detailed Calculations – To BRE 365

BS9530 –  Logging of Trial Pits