Help - Drainage Condition

[bob the builder 2]

HI All

 

I have hit a snag with a drainage condition.

 

The issue is the council have asked for a set of technical design information. ( See below)

 

Would anyone have an idea of how to answer this / someone who could help me do it ?

 

Many thanks 

Bob

 

----------------

 

It appears the issue is 

 

Design of the drainage field is the sole issue that needs addressing with regard to foul drainage.

 

 

And What they want is 

 

As I noted before, there is no further information on infiltration rate and a SuDS in relation to surface water drainage. Even though the site seems to work well with the SuDS, further details is required. In the details, there should at least be a calculated infiltration rate, the design of any required SuDS devices, such as soakaways, and any relevant calculations and drawings. The Soakaway or any SuDS device should be able to handle runoff from the whole development in and  up to 1 in 100 years 40% CC, and 10% UC storm events, and they should be managed and maintained for the entirety of the development's design life.

[ProDave]

Have you even done a percolation test?

 

[Jilly]

Something doesn't quite make sense. Foul drainage is different than a SuDs (Sustainable Drainage System) surface drainage system for rainwater.

 

Are you joining the main sewer for your foul water or having on site method of dealing with it, such as a septic tank?

 

For SuDS you basically have to demonstrate that your site won't shed more water that a green field site would after storms, and this is done by capture of the rain water and storage and then attenuation, to slow it down as it is released into the environment . There are many methods, so it depends on your site and a lot of calculations. The rule of thumb soakaway size which Building Control are usually happy with doesn't apply here. 

 

There are companies who will do this for you and one company will do the calculations if you buy their attenuation crates. Look back at the posts on here. 

 

 

 

[saveasteading]

The subject is in my expertise, but it is complex. Would need to know what you have proposed.

Using a crate manufacturer can save having to use a consultant, but you know the answer will be lots of crates. My interest has generally been to avoid lots of crates using other solutions.  Even then, there may be other considerations eg soakaway location and design.

The query re drainage field etc doesn't seem to make complete sense....I think bco trying to be helpful but getting in a muddle re terms.

As ProDave says....have you a percolation test? What are your results?

With more info perhaps we can help.

[Redbeard]

Would this help?

 

https://www.susdrain.org/resources/SuDS_Manual.html

 

The original CIRIA document is of some age (I knew it in 2008) but there is ref to an update.

 

Hope it helps.

 

I agree re the 'drainage field' and foul, but is this perhaps whatever the 'modern' version of a leach-field is, after a sewage treatment plant?

[bob the builder 2]

All

 

Many thanks for your helpful responses.

 

Having spoken with the council (amazed the picked up the phone) 

 

• 1) Design of the foul drainage field (happy with the treatment plant)
• 2) Information on infiltration rate and a SuDS in relation to surface water drainage 

 

Any tips on how / who could help me do this design / Cals would be appreciated

 

Bob 

[saveasteading]

You can do this. Calculating the percolation rate requires a spade for a small hole, a bucket and a watch.

It is not worth fiddling the results as it is you who will have stinky ground.

read here and come back with any queries.

https://www.jdpipes.co.uk/knowledge/sewage-treatment/how-to-perform-a-percolation-test.html

 

then write it up on a posh table  to inspire confidence.

[saveasteading]

it is all explained here too.

https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/442889/BR_PDF_AD_H_2015.pdf

[bob the builder 2]

All

 

Thanks again for your responses.

 

I should have said i have already done a percolation test and supplied the results to the council.

 

(The V_p (percolation value ) is 30 and the calculation suggest a field size of 60 (i assume meters)

 

Given the council already has this data it appears they are asking for

 

- a design for the drainage field for foul and for the rainwater 

- A calculation showing the rainwater drainage can handle ''up to 1 in 100 years 40% CC, and 10% UC storm events.

 

 

Any ideas on how to do these elements gratefully received 

 

Bob