Is a drainage field required for a sewage treatment plant?

[flanagaj]

Just looking at the planning application that was approved for the plot we are in the process of purchasing.  The PP used Nitrate mitigation calculations based on a Graf One2Clean system, but when I look on the drawings, I do not see any provision for a drainage field.  Is that because a sewage treatment plant can feed it's water into the same soakaway as that used for rainwater?

Maybe drainage fields only apply for the traditional septic tank based systems?

[Kelvin]

No. The design of both types of soakaways is different. Certainly mine are. Graf have some information on their website. 
 

https://www.graf.info/en-gb/knowledge-hub/blog/does-a-sewage-treatment-plant-need-a-soakaway.html#:~:text=Even though they can be,would have a larger surface

[Jenki]

1 hour ago, flanagaj said:

Is that because a sewage treatment plant can feed it's water into the same soakaway as that used for rainwater?

In Scotland my BCO was not having the two mix, although topography and make up of the land will see the two mix fairly quickly as they both run to an old field rubble drain and off to the coast 500m away.  

[nod]

16 minutes ago, Jenki said:

In Scotland my BCO was not having the two mix, although topography and make up of the land will see the two mix fairly quickly as they both run to an old field rubble drain and off to the coast 500m away.  

As above When it comes to drainage Planning has little to do with it With BC having final say 

I found that Structural engineer and BC are usally on the same wave length when it comes to this Chick it at the SE for a drawing 

 

[flanagaj]

 

1 hour ago, Kelvin said:

No. The design of both types of soakaways is different. Certainly mine are. Graf have some information on their website. 
 

https://www.graf.info/en-gb/knowledge-hub/blog/does-a-sewage-treatment-plant-need-a-soakaway.html#:~:text=Even though they can be,would have a larger surface

 

Thanks for the link.  I am rather surprised that the PP had no mention of the required drainage field.  The tank cannot feed into a water course as there isn't one in the vicinity, so it will require a soakaway of some sort.   I suppose a percolation test is required to ascertain the associated sizing.  Tank is a 1-5 person system.

[flanagaj]

Does anyone have any idea of how I can ascertain that the site meets the required points of the regs?
 

We will treat HM Governments Building regulations 2010, Drainage and waste disposal section H2 as the primary reference as it was issued after BS 6297: 2007. Just to be clear this is a summary and the full documents should be read and understood if you intend to carry out this work yourself.

• A drainage field must be at least 10m from any watercourse or permeable drain.
• It must be at least 50m from the point of abstraction of any groundwater supply and not in any Zone 1 groundwater protection zone.
• At least 15m from any building.
• Sufficiently far from any other discharge to ground to ensure the overall capacity of the ground is not exceeded.
• The field must be down water/slope of any groundwater source.
• No underground services or water pipes are allowed to be located within the dispersal area.
• No access roads, driveways or paved areas should be located within the disposal area.
• A percolation test must be carried out, please see our guide.
  
  There is also a great deal of requirements listed on the Environment Agency web site (General binding rules: small sewage discharge to the ground - GOV.UK (www.gov.uk))
  
  Will the solicitor dealing with the purchase be covering these points or is this something that I need to be doing myself?

 

[ProDave]

18 minutes ago, flanagaj said:

Thanks for the link.  I am rather surprised that the PP had no mention of the required drainage field.  The tank cannot feed into a water course as there isn't one in the vicinity, so it will require a soakaway of some sort.   I suppose a percolation test is required to ascertain the associated sizing.  Tank is a 1-5 person system.

This should be checked before you bought the plot.  You WILL need a drainage field. And depending on the percolation test results it might end up using a lot of land.  I do hope you have enough land to accommodate it, or an agreement with a neighbouring land owner for the drainage field to be under their land.

 

It is perfectly possible to get planning permission for a house you cannot actually build or cannot occupy if you cannot get a drainage solution.

[flanagaj]

6 minutes ago, ProDave said:

This should be checked before you bought the plot.  You WILL need a drainage field. And depending on the percolation test results it might end up using a lot of land.  I do hope you have enough land to accommodate it, or an agreement with a neighbouring land owner for the drainage field to be under their land.

 

It is perfectly possible to get planning permission for a house you cannot actually build or cannot occupy if you cannot get a drainage solution.

Plot is in the process of being purchased, and am just doing due diligence before any exchange occurs.  So now I know it does require a drainage field, then I need to go back to the vendor and ask the questions.  So would you advice a percolation test be performed, even though the British Geological Survey have the soil type as loamy / free draining, and the water table at a depth of 30m (property next door has a well)?

The plot is large enough, but as I have no idea what size the drainage field will be for a 6 person sewage treatment plant, it's difficult to actually answer that question.  

[ProDave]

I would organise a percolation test.  Only then can you calculate the area of land required, and then with that, and the limiting distances to buildings etc, work out just where it can actually fit on the plot.

 

Our previous house required 85 square metres of soakaway.

[flanagaj]

4 minutes ago, ProDave said:

I would organise a percolation test.  Only then can you calculate the area of land required, and then with that, and the limiting distances to buildings etc, work out just where it can actually fit on the plot.

 

Our previous house required 85 square metres of soakaway.

Agreed.  I will get this arranged ASAP.

Thanks

[Kelvin]

One of the first things I did after making our offer was carry out a land survey which included a percolation test and soil analysis in the rough area the house was likely to go. The farmer provided the tractor and an IBC. You can do the percolation test yourself but I lived in England at the time so was easier to get a proper survey. Part of the survey report included an outline design and location for the soakaway that took all the bylaws into account that you list above. 

[saveasteading]

The Scottish reg's contain a formula for the drainage field size, allowing a 20% reduction from that for a septic tank to that for a packaged treatment tank. This is a ridiculously small reduction in my opinion, and seldom  insisted on from what we hear.

 

The English reg's used to be the same, from memory, but now appear not to require a drainage field for a package plant: which I think is sensible.   

 

 

Note that there is no mention of a drainage field, whereas there is in clause 1.3 for a septic tank.

Plus, how could they be more economic unless there is no need for a drainage field?

 

 

I welcome any proof to the contrary (building inspector asking for it doesn't count).

(Welcome isn't the right  word.....as I hope none of us needs a drainage field.)  

 

I've also noticed that the government regulation, as linked above, describes treatment packages as being mechanically aided. This omits the middle ground of a non-mechanical 3 stage tank which works pretty well but is not generally available these days......I wonder if the Scottish rules were designed for this and have never been reconsidered.

 

This may not help when the planners state a P limit, but that's another matter.

[ProDave]

^^^ ALL that is saying is a TP can discharge to a watercourse, but a ST can't so must drain to a soakaway.

 

If you have no watercourse available it will need a soakaway.

 

In Scotland SEPA are less keen on discharge to a watercourse and only allow it if no suitable land drainage option is available.  Yet SEPA are not enforcing existing septic tanks discharging to a watercourse to be upgraded

[saveasteading]

2 hours ago, ProDave said:

If you have no watercourse available it will need a soakaway.

It has to go somewhere. The Scottish regs say, to a drainage field , @ProDave 's 85m2. Ours was even more but we haven't got round to the phase B bit yet and the BCO was happy anyway.

But apparently, acc to the jcb operator, a soakaway (pit of rubble) is usually accepted.

My premises is that the English regs make no such demand. At most it would be a pit or lateral soakaway for the daily amount of water going through, say 1000 litres, not as additional treatment.

2 hours ago, ProDave said:

SEPA are not enforcing existing septic tanks discharging to a watercourse to be upgraded

It's government policy according to how old it is. 

[ProDave]

9 hours ago, saveasteading said:

It's government policy according to how old it is. 

I had quite a "discussion" with SEPA when I registered the TP on our new build, in fact I actually raised a complaint.  The gist of my complaint was I paid what I thought was a high fee just to enter some VERY basic details on a website and immediately got my registration number.  They NEVER asked for any details about the treatment plant whatsoever.

 

During this discussion I raised the question as to why there are at least 2 septic tanks discharging into a watercourse near me, and surely now they are registered (both houses recently sold) they should be enforcing their upgrade to a TP.  The reply was we only do this in individual cases and only if there is a reported pollution incident.

[scottishjohn]

when going through same thing as you and having no flat area for a leach field 

they eventually agreed to a treament palnt -but with a reed bed or very large soakaway  that was 100yds  away from any water course 

this still did not work for me as ground is very sloping and rocky  and no space to comply

they eventually agreed to allow me to pipe out fall from treatment plant to a water course ,but stipulated much lower bod +amonia levels 

they thought they were clever in that as most systems cannnot give the low levels they stipulated

but the quamtum  system could provide levels much lower than a bio disc -- andunder what they asked for 

so armed with the test sheet they agreed to direct discharge to my water course 

normally they would want a partial soakaway or reed bed if I used a treament system with higher out put levels 

In the end it comes down to showing them that there are only certain options possible for the site and pick system with lowest pollution levels 

 best of it was the quantu system -suppiled by WTS is nearly half the polution level of a bio disc system  and half the price  £2500 instead of £5000

 

could you run the out flow to a water course or the sea ?

 

I had same problem with the fire brigade  wanting a 40000litre fire pond ,due to being more than 200m for a fire hydrant

but after talks and a site visit they could see it was not possible ,and so agreed to 5000litre pond  with  water course flowing through  it 

as it would be constantly replenished --

do some sideways thinking and challenge them for a sensible solution

Edited February 27 by scottishjohn