Are drainage fields/mounds required for packaged treatment plants with tertiary treatment?

[Drellingore]

Approved Document H2 section 1.54 details the restrictions on discharges from packaged treatment plants. This to me suggests that discharging directly from a packaged treatment plant is an expected outcome.

 

Approved Document H2 section 1.26 says that drainage fields/mounds "provide secondary treatment to the discharge from a septic tank or package treatment plant."

 

The thing is, I'm looking at combining a Rewatec Solido Smart PTP (which has a primary tank, and does secondary treatment) and a battery of Tricel PuraFlo modules to provide tertiary treatment and hopefully get BOD, SS, and NH4 all under <1mg/L.

 

So is the drainage field required for spreading out the discharge (improving percolation and avoiding a soggy bog), for secondary treatment via aerobic bacterial processing, or both? If it's only the middle option, then perhaps I don't need to consider one.

 

Any examples of where this has been allowed or links to relevant planning regulations would be much appreciated.

Edited January 18, 2023 by Drellingore
Making subject more specific

[Drellingore]

Hmm. The "systems you must have" section of this Government web page seems fairly clear by including this as number 3 in the list of mandatory systems:

 

Quote

The system discharges the treated effluent to the ground through the infiltration system or drainage field.

 

Unlike Approved Document H, this guidance seems to emphasise infiltration more than treatment.

[Temp]

Not sure if this is latest rules but..

https://www.homeseptic.co.uk/does-a-sewage-treatment-plant-need-a-soakaway/#:~:text=A Sewage Treatment Plant does,not require a Drainage Field.

Quote

 

Does a Sewage Treatment Plant need a Drainage Field?

 

A Sewage Treatment Plant does not necessarily need a drainage field. A Sewage Treatment Plant can discharge directly to a drainage ditch, watercourse or river. This discharge does not require a Drainage Field. Permission from the EA will only be needed if this discharge exceeds 5m squared. 

 

 

Quote

With consultation with Building Control, Infiltration tunnels can be used which vastly reduce the size of discharge to ground. Infiltration tunnels also allow a much better functioning system. They also reduces the cost. In reality, most people cannot physically fit drainage fields in their garden in line with the Environment Agency’s guidelines. We can walk you through the options available here.

 

 

Not sure if they mean "squared" or "cubed"?

 

 

Edited January 18, 2023 by Temp

[Temp]

But then..

https://www.gov.uk/guidance/general-binding-rules-small-sewage-discharge-to-the-ground

 

Quote

 

Use the correct treatment system (rule 5)

 

You must use a septic tank or a small sewage treatment plant to treat the sewage and then discharge the waste water to ground through a drainage field.

 

A septic tank is an underground tank where the solids sink to the bottom, forming a sludge, and the waste water flows out to a drainage field.

 

A small sewage treatment plant, also known as a package treatment plant, works in a similar way to a septic tank but uses mechanical parts to treat the waste water to a higher standard before it goes to a drainage field.

 

A drainage field, also known as an infiltration system, is a series of pipes with holes placed in trenches and arranged so that the waste water can trickle through the ground for further treatment.

 

The system you use must meet the relevant British Standard.

Continues..

 

So it seems a drainage Field is required now but there might be room to negotiate alternatives with Building Control.

Edited January 18, 2023 by Temp

[Drellingore]

Thanks, @Temp! I think the information from that post comes from the General Binding Rules [EDIT: this is older than the link @Temp provides in the next post] for Small Sewage Discharges. That does however put it in conflict with Approved Document H2:1.54, which says PTP discharges should be sited "at least 10m away from watercourses." I'd guess that maybe the authors of H2:1.54 are assuming a discharge to ground, which would make sense, as it's not really a discharge to ground if it's really close to a watercourse

 

17 minutes ago, Temp said:

Not sure if they mean "squared" or "cubed"?

 

The General Binding Rules say cubed, which makes sense as it's a measure of volume, so I think you've spotted a typo on their part.

Edited January 18, 2023 by Drellingore
highlight link to out-of-date information

[Drellingore]

Ha, you beat me to it  Note to other readers, my link to the General Binding Rules is older than the one @Temp posted, so prefer that link over the one I posted.

Edited January 18, 2023 by Drellingore

[ProDave]

There are two completely separate issues, you need to separate them.

 

1) does the system used need a drainage field to provide secondary treatment?  I would not personally install such a system now.

 

2) whatever system you install it produces water.  that has to go somewhere.  Assuming it is a treatment plant that has no requirement for secondary treatment, then that could go to any of the different forms of land drainage, or it could go to a watercourse.  Local bodies like the Environment Agency or SEPA in Scotland often need to licence a discharge to a watercourse.

[saveasteading]

3 hours ago, ProDave said:

does the system used need a drainage field to provide secondary treatment?  I would not personally install such a system now.

I read the regs as, yes it does. The formula is based on volume of water and percolation rate, then allows 1/3 reduction for a trestment plant. That is a crazily small reduction.  

The resulting drainage field is then stupidly huge. For a 4 bed house on clay you could be in the 100m2 of drainage field area

 

My solution is to calculate  draw the whole thing, then do it in phases...with phases 2 and 3 taking a while.

 

The jcb driver said he has put in dozens of tanks, but never seen more than an old fashioned soakaway...so bco doesn't seem interested.

But then, the jcb driver hadn't seen anyone checking if the tank was level, or being surrounded with gravel or...   etc.

 

Drainage tunnels seem no different to a perf pipe with lots of gravel. If i was a bco i might accept that as a reasonable equivalent.

.

 

[Drellingore]

As ever, thanks for your input y'all.

[HughF]

Could you not provide the required secondary treatment in a much smaller package by building a percolating filter? That’s what we’ve got as a second stage after our septic. Ours is 4ft cubed, blockwork, with and in at the top and and out at the bottom.

 

Ours uses a coke bed but I understand that nowadays injection moulded plastic biofilm carriers are abailable.

 

[PeterW]

Reed bed ..??

[Drellingore]

Hmm, the plot thickens. It turns out that the farmer who worked the site previously had a "land drain" installed, which appears to be a pipe that connects to the surface water sewer for the road adjacent to the site. That in turn allegedly goes to a ditch about 50m away on the other side of a field.

 

I haven't yet found anything that says I could make use of this. Form B6.5 mentioned discharges to surface water, but it seems to assume that you're in control of the pipe that joins that surface water, as the last 10m is supposed to be permeable. In this instance I don't even know where exactly the surface water sewer drains to, and the chances are that it's not somewhere that I own.

Edited February 13, 2023 by Drellingore

[crooksey]

If you can expose or trace that land drain with CCTV survey, I am sure a decent building controller would approve it. Especially if using a good quality treatment plant, aslong as the water is of a good standard and can be taken somewhere all year round, thats all the matters.

 

You will also need to check with the owner of the surface water sewer.

[Drellingore]

4 minutes ago, crooksey said:

You will also need to check with the owner of the surface water sewer.

 

Thanks for the reply! Any idea who this might be? It's a bit odd in that there are drains next to the road, and then I'm told that they apparently go under another farmer's field to discharge in a ditch.

[crooksey]

Any sewer pipe that is owned by the water company is there responsibility, it may not be owned by them, easy way to tell is request a sewer map from them for that area. Chances are it isn't owned by them and its just "there", or it was an open ditch that someone put a culvert in years ago.

 

If it isn't on the sewer map, get a CCTV survey done, see where it goes to and check with building control and see what they say.

[Drellingore]

20 minutes ago, crooksey said:

Any sewer pipe that is owned by the water company is there responsibility, it may not be owned by them, easy way to tell is request a sewer map from them for that area. Chances are it isn't owned by them and its just "there", or it was an open ditch that someone put a culvert in years ago.

 

If it isn't on the sewer map, get a CCTV survey done, see where it goes to and check with building control and see what they say.

 

Ta. It seems only foul sewers turn up on the maps, so CCTV survey it is!

[saveasteading]

Roadside ditches belong to the LA.

 

The likelihood of a farmer installing anything but the cheapest drain, is low. so it is likely to be a perforated coil pipe, and may not even be lined with membrane or surrounded with any sand or gravel, or even be laid to consistent fall.

(In which case it may silt up or be blocked by roots in the future.)

 

In that case it would already be a primitive french drain, and might suffice in itself. 

 

the amount of drainage field the reg's require for treated water is crazy. if i was a bco I would allow less when properly justified. It seems from discussion on here and with installers that very few installations are to the rules.

Therefore connecting to an existing water course has to be favourite.

Talk to BCO and he may just advise a simple soakaway.