Percolation test fail - sewage options?

[saveasteading]

3 minutes ago, ProDave said:

The USP of the puraflow seems to be you don't need a soakaway, it will just drain into the space of the ground it occupies.  Building control here did not agree with that

Correct by the BCO.  Nonsense by Puraflow.

If the ground can't absorb it, then it will overflow and run on the surface. Puraflood.

The volume isn't high, but still has to be catered for.

 

 

4 minutes ago, ProDave said:

20% less area of soakaway for a treatment plant vs a septic tank.

This is a remnant from when treatment tanks were a new thing. Septic tanks  emit a still filthy but very active liquid, and the vast area of the gravel surfaces allows it to cling to gravel and degrade,

They allowed a very ungenerous 20% reduction in area for properly treated water.I designed for this and we installed phase 1, but we haven't got round to Phase 2, and the BCO still says he has never seen as much as we put in.

 

I've looked at the liquid coming out of modern tanks (I've done 4, I think) , and it looks clean and doesn't smell. They have rightly stopped suggesting you could drink it though!

 

[saveasteading]

23 minutes ago, ProDave said:

Building regs in Scotland at least allow you to have about 20% less area of soakaway for a treatment plant vs a septic tank

I've looked again at the English reg's. My interpretation is that the huge drainage field only applies to septic tanks, and that treatment plant outflow does not need further treatment. ie not 20% reduction but 100%.

It doesn't say that it is not necessary, but the drainage field is applied only to the section on septic tanks, It is silent on the matter in the treatment tanks section other than that outflow must be 10m min from  building or watercourse. That fits with the @ProDavelogic above.

 

That's certainly what I've worked to before in England. I think the 20% thing used to apply but has disappeared at some stage.

[HighlandHopeful]

On 31/08/2023 at 12:44, JohnMo said:

We failed our test, water ran away to quickly - sand. If you read sepa guidelines a fail doesn't matter if it fails by flowing away to fast or slow.  The sizing guidelines are same either way when you are outside the pass criteria.

 

We just put in a big soakaway.

Hi JohnMo - which SEPA guidelines are you referring to in this message, if you can remember? We had extremely slooooooooow drainage of the holes, it would be good to know what sizing guidenlines you are referring to? Thanks!

[JohnMo]

1 hour ago, HighlandHopeful said:

Hi JohnMo - which SEPA guidelines are you referring to in this message, if you can remember? We had extremely slooooooooow drainage of the holes, it would be good to know what sizing guidenlines you are referring to? Thanks!

It was the soak away area design guidelines, it states sizes for differing drain away time from the perculation test. But states if it fails the perculation test, you size to a given criteria.

[saveasteading]

3 hours ago, HighlandHopeful said:

what sizing guidenlines you are referring to

The Scottish and English guidelines are almost identical, but not quite. If one doesn't suit then use the other and you should be ok.

BUT if you can't make it work by numbers then use logic. Where does water go now? 

AND if in trouble, go back to page 1. 'the Regulation' .  Paraphrased It will say that " water must be disposed of to cause no trouble or flooding or whatever.  Using the following guidelines will satisfy the requirement."

 It does not preclude other solutions.

 

BTW the issue with percolation being too fast is that it can create sinkholes. That happens with Kentish (etc) chalk. It will not happen with glacial moraine, which is just short of being sandstone until disturbed.

Too slow and a solution is to  spread it over a lot of area, in different directions rather than a 'field' then with an overflow to a lagoon, where the head of water helps and wind will evaporate a fair amount. The numbers still won't work but the reality usually will.

[ProDave]

@HighlandHopeful do you have a watercourse withing reach?  That solves all your problems.

[HighlandHopeful]

13 hours ago, ProDave said:

@HighlandHopeful do you have a watercourse withing reach?  That solves all your problems.

We have a couple of dry-ish ditches, so piping from the sewage treatment plant to the ditches (via a rumble drain if required) is our preferred option. I have read your responses to various threads on here - thank you, you are all so infinitely helpful!

 

What I'm a bit confused about is what to start off with in the building warrant application, I want to go in confident with a solution (pipe to the ditch) but that's not listed as one of the solution in the Building Standards handbook, but do the BS people not care as long as you've done your option pros and cons relevant to your site and situation?

 

The BS handbook says (section 3.9.2) that with very slow percolation test, options are soakaway mound, or any of the options for 'slow' that don't require infiltration, which are 'constructed wetland', a vague 'proprietary filtration system' (but is filtration infiltration?) or a vague 'other equivalent filtration system'.

SEPA say talk to Building Standards department on this website here https://www.sepa.org.uk/regulations/water/septic-tanks-and-private-sewage-treatment-systems/private-sewage-treatment-system-registration-guidance/discharging-to-land-via-a-soakaway/ I haven't found anything more useful from SEPA (actual guidance docs) so if anyone has a reference that would be great.

 

I saw your (ProDave) comments elsewhere about re-doing the percolation test to show the situation at ground level (i.e. 300mm cube at the top, rather than digging down to the 900mm of where we would have a soakaway if we had a soakaway), haven't done that yet  but if I want to lead the BS people and SEPA to allowing us to discharge to the ditch, what is the benefit of doing the ground level perc test? Or is it because their next preference after a 'normal' soakaway is a mound soakaway so you have to go through that (and discounting it) before resorting to ditch discharge?

 

For context for you and @saveasteading, our 900mm percolation holes drained 0mm and 40mm in 24 hours. They were done last week, obviously in winter, water table high and all that. The land where we are building the house is peat over clay, currently covered partially in heather. When it rains the rain wanders off down the steep hill in front of our plot towards a track down to the beach. The track has a ditch next to it (dry). The land to the ditch is in our/family ownership.

 

Another option could be pumping up to a field (also in family ownership) and putting in a drainage field, but with those percolation rates, I think the drainage field would be bigger than the physical field. 

 

Thanks  

[saveasteading]

If you use the ditch, will the water flow away ( and where to?) Or sit there until it dissipates?

Any idea what the ditches were dug for?

[HighlandHopeful]

31 minutes ago, saveasteading said:

If you use the ditch, will the water flow away ( and where to?) Or sit there until it dissipates?

Any idea what the ditches were dug for?

Hiya

We have never really seen them with running water in...

They are at the side of a dirt track down to the beach that was put in in the 80s to allow tractor access to lower fields at the beach. The ditches were part of that digging, so to allow surface run off from the track to go into the ditch rather than run down the hill and make the track muddy.

 

 

 

[saveasteading]

53 minutes ago, HighlandHopeful said:

never really seen them with running water in..

Then be sure. Inspect during and after the worst rain and take pictures.

 

My hunch is to use french drains all the way to these ditches. That will spread your water over a big area and avoid affecting the peat. It will then spread the same water as currently, across the clay. Big storms reach the ditches.  You might put a slight dam in a ditch to hold water back.