SuDS and Off Mains Drainage : beware, here be dragons

[ToughButterCup]

SuDS: Sustainable Urban Drainage System and Off Mains Drainage. Here be Dragons.

Call me naive, but here's how I found out that I had responsibilities in this area. That was in July 2014. And since then, I have been working on it sporadically - there has always been a brighter fire burning at my feet. But now that my EPS application has been delayed (please don't ask me for details: my doctor has told me not to talk about it ) I have bitten the SuDS bullet.

Part of my strategy in dealing with the issues surrounding SuDS is to listen to interminable discussions at Parish level about local planning applications. For some reason - without rationale or considered argument - almost all housing development is   held to be a bad thing. Not exclusively, you understand, but generally it's a bad thing.

The Fylde Peninsular (where we live) was the dumping ground in that last Ice Age for a good deal of what became clay -  Glacial Till. And that makes drainage difficult. And so soak-aways are a bit of a problem. Not to mention off mains drainage. 

And so when, at local level, with a good deal of huffing and puffing, opposition to development occurs, most of the opposition focuses on completely irrelevant issues such as this example.

SuDS is a standard requirement. Off mains drainage (locally) and SuDS cannot be avoided. And if you can't sort out a soak-away because of the clay  you can't have a house.

And here's how the trap is set. The details for SuDS and Off Mains drainage are agreed at planning level, but enforced by your BCO. So -stupidly in my opinion- you can commit to all that expenditure and actually build the house but fail to provide the necessary documentary evidence until sign-off looms large. 

No SuDS, no off mains, no house . Not a lot of people know that. Quite why, I'm not sure.

 

[Ferdinand]

A powerful point here can be if your plot has an established right to drain off site, which could take many forms.

e.g. If there is an existing ditch, you may be able to use it if you can demonstrate that there will be no increased flow from your new house.

On a larger scale that might be via a balancing pond and a controlled outlet.

Ferdinand

 

[ToughButterCup]

16 minutes ago, Ferdinand said:

[...] a balancing pond and a controlled outlet.

 

PMSL 

[Ferdinand]

On 15 June 2016 at 07:31, recoveringacademic said:

PMSL 

Heh.

Remember that my project is a several acre housing site.

In our case we have a general policy requirement from I think the LPA that the runoff from any housing estate must be the same as or less than the open field that exists now. We have established agricultural drainage ditches, and our proposed SUDS was designed by no less than Mott McDonald. Some of the lessons may be applicable.

I have no idea what happens to a balancing pond regulations-wise when the "newts in suits" move in.

There are also things such as mega-underdrive-storage-areas a la Jeremy, or large diameter drainage pipes (e.g. 600mm) that can store water.

Or you can include discharge to a drain as part of your PP as a final resort.

Ferdinand

 

[ProDave]

Yes I know this topic very well. We have a burn through the garden, originally SEPA said no to discharging to the burn, so I ended up designing a filter mound system and that is what planning passed.

When it came to the building warrant, I suddenly found building regs had changed and the area of land I could put a filter mound on had shrunk, and was no longer big enough. For a while I had no drainage solution = no house, until SEPA changed their mind and said "why not discharge to the burn"  Problem solved and we are now proceeding but it was a VERY worrying period.  Aparently SEPA only allow discharge to a watercourse as a "last resort" and we had reached that last resort stage.

[Jeremy Harris]

We're on clay and as Ferdinand says, I fitted a large underground surge run-off tank.  This drains from one corner to a thin layer of permeable soil, which I know for sure just drains under the lane into the stream.  We were forbidden from draining rain water run-off into the stream, but immediately given a licence to discharge sewage effluent to the same stream (yes, you too can scratch your head in puzzlement at the workings of the Environment Agency, who control both these aspects, from different offices).

When digging the services trench around our plot we uncovered an old clay land drain pipe running down the side of the lane, then under it at the bottom and discharging into the stream.  It had been put in to take the run off water from the steep lane alongside our plot, and as it was unjointed clay pipe my guess is that it was probably Victorian.

What I eventually found was that the building inspector was OK with the principle that Ferdinand has mentioned - that the development won't change the flood response time.  Our surge storage actually means we've slowed the run-off time, as our site was a clay slope that allowed water to run off freely, cross the lane and flow into the stream.  Now it all collects in the tank and runs off unseen underground.

[ToughButterCup]

17 minutes ago, ProDave said:

[...]

until SEPA changed their mind and said "why not discharge to the burn"  Problem solved and we are now proceeding but it was a VERY worrying period.  Aparently SEPA only allow discharge to a watercourse as a "last resort" and we had reached that last resort stage.

Hmm, a very important lesson for everyone Dave.

Silly, isn't it that the regulations vary by administrative area rather than the local geology. 

[ToughButterCup]

3 minutes ago, JSHarris said:

[...]

What I eventually found was that the building inspector was OK with the principle that Ferdinand has mentioned - that the development won't change the flood response time.  Our surge storage actually means we've slowed the run-off time, as our site was a clay slope that allowed water to run off freely, cross the lane and flow into the stream.  Now it all collects in the tank on runs off unseen underground.

And that's what we are working towards.

As sheer luck would have it we have an area of garden (orchard) that was a deep 'pit'. The previous owner filled it in with rubble, hardcore, gravel, the odd old gate post  and dozens of tonnes of mushroom compost. And we've had a trial pit dug to 2 meters + (the original level) to look at the water table level. To date completely dry, even in heavy persistent rain. Talk about lucky........

[ToughButterCup]

52 minutes ago, Ferdinand said:

I have no idea what happens to a balancing pond regulations-wise when the "newts in suits" move in.

You know how to tweak a man's ire don'tcha?

Still, if I can't take a joke, I shouldn't have applied for PP should I?

[Jeremy Harris]

7 minutes ago, recoveringacademic said:

Hmm, a very important lesson for everyone Dave.

Silly, isn't it that the regulations vary by administrative area rather than the local geology. 

It's barking mad!  In England and Wales, the EA much PREFER that you drain a treatment plant to a watercourse that runs all year around, and consider land drains and soakaways to be a less preferred option.  In Scotland SEPA take the opposite approach.

Given that both bodies have essentially the same responsibilities, you have to wonder quite what the rationale is behind their decision making processes.

[ProDave]

Yes as Jeremy says, SEPA have exactly the opposite view to the EA.  At the start I even measured the flow rate of the burn (which turned out to accord with their official figures) and worked out the dilution rates but the original answer was a firm NO and it was SEPA that suggested the filter mound system.

And yes it is a lesson learned that if you take to long, building regulations can change and what was okay, is no longer allowed.

Discharging to the burn is the simplest and cheapest option so I am very pleased that is what we have ended up with. The filter mound would have used about £1000 worth of graded sand and would have left a "hill" in the middle of the garden, and needed a pumped output on ther treatment plant.

[Stones]

I've had similar experiences with SEPA in the past as well.  In a way, I understand their logic, not wanting to risk adding pollution from a poorly maintained system into a watercourse, however, the fact that you can do it so easily elsewhere in the UK, just bonkers.

Interestingly, the system (up here at least) for applying for consent to discharge has recently changed.  When I applied late last year, all I was asked to provide was a grid reference for the soakaway position.  No requirement for treatment data / figures as per my last house / application - in fact SEPA were happy to accept aseptic  tank if that is what I wanted to install!  

[ToughButterCup]

1 hour ago, Stones said:

[...]

Interestingly, the system (up here at least) for applying for consent to discharge has recently changed.  When I applied late last year, all I was asked to provide was a grid reference for the soakaway position.  No requirement for treatment data / figures as per my last house / application - in fact SEPA were happy to accept a spetic tank if that is what I wanted to install!  

It's called Joined-Up-Thinking. 

How desperately damn stupid.

 

[Gone West]

My Highways Dept. and BCO were happy for me to discharge roof drainage directly onto the road. The water table can vary by 2.5m from road level downwards and they accepted that trying to put large volumes of water into already saturated ground was pointless. The road runs gently down to a ditch and then stream.

[Triassic]

There is no mention of SUDS in my planning approval, maybe I'll just keep quiet !

[Jeremy Harris]

9 minutes ago, Triassic said:

There is no mention of SUDS in my planning approval, maybe I'll just keep quiet !

There isn't in mine, either.  I still had to comply with it, though, as it's now a bit of legislation.  It was passed into law in 2010, although it's fair to say that local authorities have not acted swiftly to set up the required approval bodies.

However, I found that building control dealt with it as a part of general drainage, and wanted to see that whatever we installed was SUDS compliant, even though there was nothing on our planning permission about it, apart from a mention in the D&A by me, and the D&A doesn't seem to have been referenced in our decision notice, so is non-binding (something I thought was a bit curious).

As always, it will probably come down to your building inspector as to what they want to see to handle surface water drainage.  Some may want full SUDS compliance, some may not; it's probably just pot luck which you get. 

[joe90]

I talked to my building inspector about soakaways and pointed out that a big hole in clay was a pond !!! I created a French drain to a ditch and he agreed it was ok. This was for the garage, I hope he has the same attitude about the house !.

[gc100]

Bringing this thread back to life. I'm a bit worried about my situation in regard to drainage. For our planning we had to specify the treatment plant and where the drainage would go. As we are in open countryside there is already a drainage ditch that runs down the side of the barn we are converting and off down the edge of the field and wood  and eventually ends up draining into the wood at the bottom about 200meters away. We specify the discharge would run into this ditch. This was accepted by the LPA.

However reading this : https://www.gov.uk/guidance/general-binding-rules-small-sewage-discharge-to-a-surface-water

There is a section that says:

 

"Make sure the surface water has flow
New discharges are not allowed to a ditch or a surface water that does not contain flowing water throughout the whole year. That is unless there is a drought or an unusually long period of dry weather.
New discharges to watercourses that seasonally dry up are not allowed under the general binding rules, nor are discharges to enclosed lakes or ponds."

 

There is a reasonable slope to the ditch so the water does not sit in it, and drains quickly. Its dry in the summer as obviously there is little rain in Norfolk relatively speaking and all the ditches on the farm dry out.

Speaking to the company supplying the treatment plant they don't seem worried about this fact, however I'm not very confident and get the impression it depends on the BCO person who turns up and whether its been raining recently.

 

If they turn this down and say I cannot use the ditch, I presume they will want me to make some form of drainage field? My problem is that due to the slope of the site this would need to be in the wood which is part of my site, which is not a good idea as it would damage roots of the treats and I suspect I wouldn't be allowed. 

 

Any guesses?

 

Also why do they not want discharge into a dry ditch?

 

Edited October 15, 2019 by gc100
I just released this post is in the wrong section, but I don't seem to be able to delete it. Sorry

[ProDave]

The dry ditch thing is because effluent discharge to a watercourse needs a certain dilution ratio.  Before SEPA would give me a discharge permit for the burn I had to set up a temporary V notch weir to measure the flow rate of the burn, and they then told me it was what they expected and the dilution rate would be acceptable.

 

@joe90 I am sure has permission to discharge to a dry ditch.

[gc100]

Ok thanks. What exactly is the definition of 'watercourse' ??  I still don't really get it though as the discharge would just soak into the (dry) drainage ditch and not go anywhere .

[ProDave]

So what you are proposing is an open infiltration field, which is not allowed.  Cover it over and make it a proper underground infiltration field and the problem goes away.

[gc100]

2 minutes ago, ProDave said:

So what you are proposing is an open infiltration field, which is not allowed.  Cover it over and make it a proper underground infiltration field and the problem goes away.

 

Ok thanks ProDave. So could I put in say something like a 10 meter perforated drainage pipe down and cover over before running into the open part of the ditch? 

[ProDave]

Building control will normally want to see a proper design based on a percolation test from which you can work out the area of land you need for the soakaway system.

[joe90]

22 minutes ago, ProDave said:

 

@joe90 I am sure has permission to discharge to a dry ditch.

 

I do, the vortex treatment plant we have can discharge to a ditch that is dry for part of the year as long as it’s connected to it by a rumble drain (perforated pipe buried in drainage stone).

[gc100]

1 minute ago, joe90 said:

 

I do, the vortex treatment plant we have can discharge to a ditch that is dry for part of the year as long as it’s connected to it by a rumble drain (perforated pipe buried in drainage stone).

 

Was that given by building control or EA?