Category Archives: Drainage

Do I Need To Do A Percolation Test?

Leave a Reply

Do I Need To Do A Percolation Test?

Who Is Asking For The Percolation Test Results

If you are reading this mt guess is that you have been asked to carry out a percolation test either by:

  • You Building Inspector
  • You Planning Officer

Up until about 5 years ago percolation tests were strictly the domain of building control, if they weren’t building control then they would have been carried out by a drainage engineer or a septic tank installer prior to installing a drainage field.

Percolation Testing 30cm x 30cm Hole

A building inspector might ask to see the results of your percolation testing so as to check the design of your drainage field., as might a drainage engineer if their scope does not include for obtaining the results.

What is recently new is that a planning officer may also ask for results of percolation testing. This can seam quite annoying given that it contrasts with historical requirements. However, in some cases there is a justification for doing so.

Soak-Away Testing . . . Big Hole

Why  Am I Being Asked For Percolation Testing?

If you are being asked by building regs or a drainage engineer then the answer is reasonably obvious. It is to provide data (VP Rate) so you can design the drainage field at the correct size.

But why i your planning officer (or consultee) asking for percolation testing? We would suggest there are two reasons:

  1. Less likely – The planning officer is overstretched and doesn’t have time to determine your application, and as such they will ask for this extra detail (with no real justification for doing so ) in order to buy themselves more time.
  2. More likely – The planning officer is worried that after planning is granted it may become apparent that infiltration drainage is not viable on site. Lets have look as to why this might be the case:

Why Is A Drainage Field Not Viable On My Site?

Reason 1 – Lack of Space

Is there enough room on site for a drainage field? In soils were water logging is sometimes a problem like clays. The drainage field required might be very large, you don’t know how large until you have carried out the percolation tests.

Reason 2 – Clay Soils

If the VP rate is too low. Then a drainage field may not work. If you then intend to use a drainage mound, what size will it be and will this affect the layout or the appearance of the planning proposal.

Reason 3 – Very Permeable / Pervious Ground

Just as a VP rate can be too low. It can also be too high. So f you are o a site with clean sandy soils, or gravels then the permeability might be too high. This can also be a problem on ground where the has cracks in it like limestone, you might hit a fissure and all of the water drains away very quickly. Luckily this maximum rate only applies to old fashioned septic tanks, and you can get around it by using a treatment plant.

What Can Do If I Am Asked For Percolation Tests By Planning Officer?

Follow the below handy list:

  1. Is the request justified? If you live in the middle o nowhere with huge areas for the drainage field , and geological maps show that that you will get good drainage. . . why are you being asked.
  2. In all other instances just do the tests. We can do them or you, or you can find instruction on how to do them in the building regulations.
  3. Is the VP rate too low? Investigate a drainage mound, or perhaps investigate using a treatment plant and discharging to a river. Another option might be to run a pipe (perhaps or a long way) and connect to mains sewer.
  4. Is the VP Rate Too High? Swap you septic tank to a treat plant.

A very complicated solution is a borehole soak-away. his costs a lot o money and you will need to get a licence from the Environment Agency. If you thing drilling a 30m deep hole sounds difficult . . . try getting a license from the Environment Agency.

Bored Already?

Just get us to do it for you. Please contact us for a quotation.

 

 

Application for Discharge of Drainage Condition

Leave a Reply

Application for Discharge of Drainage Condition

We have recently been engaged to discharge drainage conditions in Wiltshire. The planning approval contains 2no. drainage related conditions that we are applying to remove at the same time.

What does the condition look like?

“No development shall commence on site until a drainage strategy has been submitted
to and approved in writing by the local planning authority. The drainage strategy shall
include, as a minimum, the following information:
– Calculations and drawings for the drainage system design showing designated holding areas and conveyance routes based on no flooding on site for a 1 in 30 year rainfall event.
– Calculations and drawings for the drainage system design showing designated holding areas and conveyance routes based on no flooding on site for a 1 in 100 year plus climate change rainfall event in respect to a building (including basement) or utility plant susceptible to water within the development;
– Calculations which demonstrate that the required 20% betterment against greenfield rates has been achieved for all storm events between the 1 in 1 year and the 1 in 100year return period storm events.
– A clearly labelled drainage layout plan showing the pipe networks and any attenuation ponds. The plan should show any pipe node numbers referred to within the drainage calculations.
– A plan showing the cross sections and design of any attenuation pond and its components”

What is our response to that?

Our response to this will include a custom written report that sets out the requirements step by step, using plans and calculations.

How we can help.

If you need a planning condition related to drainage discharged then please do contact us. We provide a free of charge 15 minute consultation to help understand your requirements. Our reports are kept as simple as possible, and are typically well received.

BRE365 Soak-Away Testing in Gloucester

Leave a Reply

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

Sewage Treatment Plant Decommissioning – Devon

Leave a Reply

Treatment Plant Decommissioning – Devon 

Acting on instructions from a property owner in Bishopsteignton, Devon, Southwest Environmental Limited have been commissioned to draft a Decommissioning Strategy for a Sewage Treatment Plant.

The plant was around 30 years old, and used to treat water prior to discharging it to a river (surface water). However, around 10 years ago the development was hooked up to the mains sewers, and the treatment plant is now no longer required.

Although there is very extensive guidance available for the decommissioning of underground structures in the “Blue Book” for petrol filling stations, guidance for the removal of sewage related tanks, is some what limited. The Binding Rules for example give very scant advice, and further information given in PPG27 has now been withdrawn with no replacement made.

In this instance we authored a removal strategy based on international guidance, parallel sector guidance and review of case studies.

If you would like an opinion on decommissioning of a septic tank, treatment plant read bed or other foul water treatment system, then please contact us, and we provide a no obligation initial appraisal. We provide advice and reporting for a wide range of drainage systems.

Drainage Strategy – Amersham, Buckinghamshire

Leave a Reply
Southwest Environmental were contact my a firm of architects who required a Surface Water Management Plan (Drainage Strategy) for their site is amersham. The project involves the extension of an existing warehouse.

The additional roof area has the potential to create run-off. A design was put forward to counter this problem.

Run-Off is when water falls on a hard surface, and does not soak in to the ground. It then will “run-off” . . . but where will it go. Perhaps it is caused flooding elsewhere. This is the purpose of a Surface Water Drainage Strategy. It sets out a method for dealing with Run-Off

The report was prepared on a quick turnaround (5 working days) and submitted for review. Pending some minor amendments at request of the client the report was submitted to Chiltern District Council for Scrutiny.

Are current design avoids the use of soak-away drainage although is does recommend for some attenuation.

Drainage Report – Cullompton

Leave a Reply

Drainage Report – Cullompton

Some areas of Cullompton are designated as a critical drainage area. You may have a planning condition which states that:

“As the application site falls within the Cullompton Critical Drainage Area, please submit a Flood risk Assessment”



A flood risk assessment typical is focused on flood risk to the site, when what is required in a Critical Drainage is a Surface Water Drainage Strategy.

The way to deal with most domestic / residential drainage requirement is permeable paves, with added features. Mots consider this an expensive option, but this is due to lack of understanding.

In order to capture run off you must provide a volume of “holding” (an attenuation volume) this usually provided my the spaces between gravels in a soak-away trench.

But why not use these same gravel as a sub-base for permeable paving? You will have to import fill for driveways anyhow. You end up using the aggregate twice for soak-away and for sub-base.

Water from roofs can be fed in to the sub base, and drive water just soaks straight in, avoid the requirement for gullies etc. There are no blockages from leaves.

Application for Connection to Thames Water – Barking

Leave a Reply

Application for Connection to Thames Water – Barking

Southwest Environmental Limited have recent applied for a connect to thames water sewers, on behalf of a repeat client. The application procedure is not overly onerous, but it does help to have background knowledge of the site.

Back in 2014 SWEL produce a Surface Water Drainage Strategy for this site and so we are familiar with the asset arrangement in the area, along with the flow rates from surface and foul water outputs.

It helps if the assets in the area are understood. . . 

. . . location plans were sourced. . . 

. . . invert levels should also be considered. 

This is the more recent of numerous applications we have undertaken on behalf of developers in London. The process does take a while Fees to Thames Water are around £500, and then we would charge time on top of this.

If you need any help with applications to Thames Water or Anglian Water or others, then please get in touch.

Environmental Consultants London 

Foul and Surface Water Drainage Strategy – Seaton

Leave a Reply

Foul and Surface Water Drainage Strategy – Seaton

Southwest Environmental Limited have recently produced a Foul and Surface Water Drainage Strategy for a client in Seaton, Devon.

The report included specification of surface water sewers with calculation for attenuation in line with CIRIA guidance.

Sewers both surface and foul were specified in line with Sewers for Adoption 7.

The strategy took in the account the current sewers on site, and the locality of mains sewers in the area.