Percolation test fail - sewage options?

[Dunc]

Our percolation test failed - too wet. What are my options?

 

We're in Scotland.

The plot does not have access to mains sewers.

The trial holes were filling with water as they were dug. The engineer reported: "wet peat overlaying wet, very clayey sand."

My engineer is suggesting that the only viable option will be to discharge treated waste via pipe to a watercourse which is a few hundred meters away. 

 

Just wondering if the collective have any other suggestions?

[joe90]

I am in England but also failed the percolation test, I used a vortex treatment plant which has very clean outfall and allowed to discharge to certain water courses. Others from Scotland will be along shortly.

[ProDave]

Two options really.

 

Dig a test pit at ground level, literally a 300mm cube hole and try a percolation test in that.  If that drains away okay, then you could install a filter mound system, which is just a pile of very expensive graded sand and the drainage field on top, then covered in earth.  You usually need a pumped output from treatment plant to pump the output up to it.

 

Or if you have access to the watercourse (as in legal right to dig up the land and lay a pipe) then do that.  It is by far the best solution.

 

In my case building control rejected the filter mound and at that point SEPA agreed to discharge into our burn, but unlike in England, SEPA seem to want you to prove land drainage is not possible before they will agree.

[Dunc]

I can probably agree wayleave with the estate whose land we would need to cross for access to the watercourse.

I'd imagine a 300-400m trench & pipe might be rather expensive so was just wondering if there are other options to be considered (i.e. an above-ground solution). 

But given the general boggy-ness of the ground, even a surface-level hole will likely self-fill. 

 

Do I understand correctly then, that even after a tertiary system such as a sand mound or a co-conut filter box, there is still a requirement for the outflow to then percolate into the ground rather than become surface run-off?

 

thanks.

[Kelvin]

You already own the plot? 
 

I’d contact whoever owns the land you need to cross and get that process started now. They might say no, they might want to charge you a load of money you can’t afford so best to establish that ASAP. 

[saveasteading]

You could look into a pumped disposal system. There is a capital cost of course for a reception chamber with pump, then the length of pipe you need to reach the ditch or burn.

But it doesn't need a fall or deeply excavated trenches so it may even out. They have a float valve so they only run occasionally.

Another option might be a reed bed but research and negotiate before committing.

 

It would obv be a very bad thing for nutrients to drain into a peat bog.

[JohnMo]

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.

[saveasteading]

1 hour ago, JohnMo said:

We just put in a big soakaway.

Shouldn't that also be over a huge area to satisfy the reg's? 

But to my eyes (and it seems all bcos) that is enough.

We have the same sand by the looks of it, glacial deposits, very hard until disturbed.  All sites should be made of it.

[Dunc]

thanks for lots of thoughts.

 

We don't own the plot yet, this is part of due our diligence. Fortunately the estate we're buying from also own the land we might need to cross, so wayleave shoudn't be a problem (phew!)

 

No pump required - the plot and intermediate land falls towards the river. It's just that the river is a good 300-400 meters away so I wondered if there's an on-site solution.

 

"a fail doesn't matter if it fails by flowing away to fast or slow." - but the issue here is that if we dig a field like @JohnMo's it'll just be a swimming pool from the ground water flowing in.

 

Reed bed sounds interesting...more reading required.

 

 

 

[crooksey]

Spend the money now, lay a pipe over 400m, wont cost as much as you think and problem solved (for life).

[saveasteading]

13 minutes ago, Dunc said:

No pump required

300m is a lot of drain.

As the pump would use a small and flexible pipe (50mm?) , a big hose really, it might be worthwhile though. It could just be inserted into a slice in the ground, which will close up against the pipe. No need for careful ,gradients bedding. or intermediate chambers. Peat won't provide much support, so a gravity pipe might go out of grade easily.

Downhill makes it an easy pump so a small unit will suffice.

'Experts' will want to sell you a big chamber with pump fitted, so that it can hold waste in case of power failure. i think you just need a normal outflow chamber with a pump laid in it.

[saveasteading]

1 minute ago, crooksey said:

problem solved (for life).

You are right, if the slopes and bearing capacity allows.

It may cost more using gravity for such a distance, but the power comes free and is reliable.

[Dave Jones]

isnt it illegal to flow raw sewage into a watercourse ?

 

The trial pit shows water table near surface so rules out treatment plant ?

[Kelvin]

48 minutes ago, Dunc said:

thanks for lots of thoughts.

 

We don't own the plot yet, this is part of due our diligence. Fortunately the estate we're buying from also own the land we might need to cross, so wayleave shoudn't be a problem (phew!)

 

No pump required - the plot and intermediate land falls towards the river. It's just that the river is a good 300-400 meters away so I wondered if there's an on-site solution.

 

"a fail doesn't matter if it fails by flowing away to fast or slow." - but the issue here is that if we dig a field like @JohnMo's it'll just be a swimming pool from the ground water flowing in.

 

Reed bed sounds interesting...more reading required.

 

 

 

 

Great news you’re doing your due diligence on this I did the same. Surely this percolation test failure is a point of negotiation as it will be the same for anyone else interested in buying the plot if you didn’t. Therefore I’d making it a condition of sale that they grant a wayleave as a minimum as part of the purchase. I’d also be talking to them about how to solve the problem for both you and them by coming to some financial agreement on splitting the cost. As it’s an estate do they have access to diggers etc? 
 

Reed beds are very difficult to keep from everything I’ve read and prone to failure. 

[saveasteading]

5 hours ago, Dunc said:

to discharge treated waste

In all the above, I am assuming fully treated waste.

 

5 minutes ago, Dave Jones said:

so rules out treatment plant ?

i don't think it does.

[Redoctober]

1 hour ago, crooksey said:

Spend the money now, lay a pipe over 400m, wont cost as much as you think and problem solved (for life).

 

We had a similar issue although on a much smaller scale. That said we had to dig a trench through the farmers neighbouring field. [We too bought the land from him so we waited until he had harvested his crops before doing so. He was happy with this arrangement] - We dug a trench probably 100 m out into his field and joined the perforated pipework, which we laid onto an existing land drain, which was buried in the field. By doing so the discharge was then carried on to the water course some 150m away.

 

Could this work for you @Dunc ?

 

Total cost of this was around £2.5k 4 years ago.

[ProDave]

3 hours ago, Dunc said:

We don't own the plot yet, this is part of due our diligence. Fortunately the estate we're buying from also own the land we might need to cross, so wayleave shoudn't be a problem (phew!)

Then make it a condition of the missives that they grant a right to lay a pipe to the river if you should need to.  Get your solicitor on the case now.

[crooksey]

15 hours ago, Dave Jones said:

isnt it illegal to flow raw sewage into a watercourse ?

 

The trial pit shows water table near surface so rules out treatment plant ?

 

Decent ground management and a number of pumps, problem solved.

 

Especially with plants like a graf where you secure them with shingle, as opposed to concrete.

 

I would also want the riser 100mm above ground level (if the table was really high)

[JohnMo]

You get it easy in England, in Scotland we have to design the whole treatment system, with all supporting calculations. Get a licence from SEPA to install and operate and it has to be installed per design and any additional stipulations made by SEPA.

 

In England it seems you are able to design (maybe too strong a word -knock it up) as you see fit - right or wrong.

 

Prefer the Scottish system, it's black and white (ok or wrong)

[Dunc]

Just addressing some of these really helpful comments:

 

Wayleave won't be a problem - the estate now knows that the plot is effectively worthless without the ability to put in suitable wastewater management and they own the ground we might need to cross. Solicitors are already on the case, thanks to all who suggested. It was one of your early posts @Kelvin that made me aware we could make these investigations part of QA! But we will need to have a design and SEPA approval before we sign on the dotted line.

 

I hadn't thought about risk of a long pipe in soft ground settling - obvious when you say it! So @saveasteading you'e suggesting a small diameter "hose", (perhaps within a larger rigid pipe to prevent pinching?) being pumped so any undulation is dealt with by pump rather than gravity. Probably from a collection chamber downstream of the treatment plant so the pump only runs e.g. 1x/day and gives capacity for collection during power failure? But as @crooksey said, gravity is free. Either option will likely work though so just a question of cost and practicality.

 

Intriguing point @Redoctober if we can find a drier bit between us and the river we may not have to go all the way. Seems unlikely, but worth going bushwhacking...

 

No intention of putting untreated waste into a watercourse (or anywhere else!). Assuming we can anchor a treatment plant so that it doesn't float, and ensure air inflow and access ports are above water (and any surface flooding) I'm not sure that I see the issue with a buried treatment plant? @Dave Jones

 

The only bit I'm missing (and apologies if I'm just being thick): if we have suitably clean outflow from a treatment plant (and obviously it would have to be if it were going to the river) is there no way to discharge this within the plot via something like a sand mound? Only keen on this as it's entirely contained and within my control so if it goes wrong in future I don't have any problems dealing with it.

[ProDave]

1 hour ago, crooksey said:

 

Decent ground management and a number of pumps, problem solved.

 

Especially with plants like a graf where you secure them with shingle, as opposed to concrete.

 

I would also want the riser 100mm above ground level (if the table was really high)

I would not advise putting a treatment plant in shingle in a high water table area.  I have seen one float out of the ground.  Not pretty and not easy to fix.

 

We were wrongly advised at our last house to do that.  It is not a problem when it is full, but it means we can only desludge it in a long dry spell when the water table is low.  To desludge it in winter with the water table high would be asking for trouble.

[crooksey]

Dig a bigger hole and put some dry 5:1 mix in with the shingle then, its not rocket science it all depends on exact site conditions.  Again, anything a decent crew will overcome on the job.

[saveasteading]

1 hour ago, crooksey said:

anything a decent crew will overcome on the job.

The decent crews I have known don't have a clue on this subject.

On our recent installation the excellent jcb driver said he had put in about 30 tanks. He had never seen anyone checking the level so precisely, or using a spirit level, or having anything more than a soakaway as outfall.

I assume these installations work but sub-optimally, with potential pollution or blockages.

Then these decent gangs disappear and won't hear of any problems.

 

For anchoring weight you can use lean mix or no fines concrete but it's no cheaper unless mixed on site.

By calculating the weight required, you can minimise the concrete surround but it needs shuttering or slow work.

I would first check if any manufacturers allow the tank to be strapped to the base.

[JohnMo]

On 31/08/2023 at 10:20, Dunc said:

We're in Scotland.

Sorry just read the first post again, you do need SEPA approval to operate, the full design has to be approved by them, including make model and size of treatment plant, soakaway design etc. They will question everything we got questions on loads of stuff.

 

https://www.sepa.org.uk/regulations/authorisations-and-permits/application-forms/small-sewage-discharges/

[Kelvin]

13 minutes ago, JohnMo said:

Sorry just read the first post again, you do need SEPA approval to operate, the full design has to be approved by them, including make model and size of treatment plant, soakaway design etc. They will question everything we got questions on loads of stuff.

 

https://www.sepa.org.uk/regulations/authorisations-and-permits/application-forms/small-sewage-discharges/

We didn’t get any questions for our registration but I did provide a full ‘pack’ of information that covered every question asked. Registration was pretty quick too.