Percolation test fail - sewage options?

[JohnMo]

25 minutes ago, Kelvin said:

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. 

I did mine the heights of COVID when everyone was working from home, possibly they had nothing better to do. Plus the architect did the first submission, I just picked the pieces, "if want something doing right, do it yourself"

[Temp]

On 31/08/2023 at 11:32, Dunc said:

I'd imagine a 300-400m trench & pipe might be rather expensive

 

110 drainage pipe starts around £5/m so thats £1500 to £2000.

 

If your pea gravel was 0.25m * 0.25m * 400m thats 25m^3. 

Density is about 1900kg/m^3 so 25*1.9 = 48 tons at £45/t = £2000

 

Digger and driver for a week or is that optimistic?

[saveasteading]

Over 400m I would put in some rodding points, whether addressed by the regs or not . I haven't looked).

In theory the effluent is clean by this stage, and shouldn't ever block, and the rainwater guidelines should suffice.

[Gus Potter]

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

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."

Have come across this from time to time.

 

Yes your starting point here is to intially forget the soakaway concept and go for a packaged treatment plant. The cost of these has come down a lot over the years.

 

300 -400m is perfectly doable to pump to a water course.. you may find that a 40- 50mm diameter pipe works fine. It also does not need to be on a fall. I designed one a while back down Aylesbury way where the pipe went up hill first then down to the water course. The main thing is the dry weather flow in the water course.. SEPA do that bit of the work for you.. so you need to make any offer on the plot conditional on SEPA giving you the OK.

 

The application process is faily simple and not hugely costly, but it takes a bit of time to get SEPA to process it.

 

But I would try and lock in the seller early.. don't tell then just how you are going to resolve the problem in case they do it themselves and gazzump you.

 

Also a PTP does not need to be buried in the ground. If the house is higher and you can get a fall to it then fine. Another way is to gather the soil water from the house and pump it up into the PTP a bit like an external saniflo.. but much better. . You have options here.

 

Yes the plot is worthless so the Estate should be fine (unless they want to knock off 40+ k of the value of the plot.. subject to conditions).. all you need is 750m deep track to bury the pipe from the PTP to the water course.

 

You could maybe do a mound soakaway but these are costly to design.. lots of liability for the designer. A mound may cost 20k+  to get it right.. even then the topography of the ground and area available may make impossible.

 

 

 

 

 

 

 

 

[SteamyTea]

8 hours ago, Gus Potter said:

I designed one a while back down Aylesbury way where the pipe went up hill first then down to the water course.

Slopes rather than hills in Aylesbury.

 

You could have taken one of my Sister's boat trips and seen where it all ends up.

[saveasteading]

19 hours ago, Gus Potter said:

where the pipe went up hill first then down to the water course

Ooh. Bold. I suppose it occasionally gets so full that it gets over the hump then siphons itself empty.

I'd be nervous about a gradual buildup of jetsam in the dip.

My instinct says to keep it sloping downhill.

[Gus Potter]

On 02/09/2023 at 18:54, saveasteading said:

Ooh. Bold. I suppose it occasionally gets so full that it gets over the hump then siphons itself empty.

I took the view that as the exit pipe from the treatment plant pipe went uphill first then down to the stream that it would be running full bore on the upwards run, the treatment plant had a pokey pump.

 

From  memory I think I went for the smaller 40mm diameter pipe to make sure it ran full bore with a good flow velocity, enough to push any sediment up and over the crest of the pipe. This is a case where you could over size the outflow pipe thinking larger diameter is better.

[Crofter]

I installed a Puraflow system. Comprises conventional septic tank, pump chamber, then the clever bit which is the Puraflow unit itself. A big plastic tub filled with peat moss fibres and some piping. The effluent is pumped around that and trickles down through the peat moss, which allows for aerated breakdown, and what emerges from the holes in the bottom is fit to discharge to ground or watercourse.

The system was designed in Ireland where high water tables are a very common problem.

[crooksey]

13 minutes ago, Crofter said:

I installed a Puraflow system. Comprises conventional septic tank, pump chamber, then the clever bit which is the Puraflow unit itself. A big plastic tub filled with peat moss fibres and some piping. The effluent is pumped around that and trickles down through the peat moss, which allows for aerated breakdown, and what emerges from the holes in the bottom is fit to discharge to ground or watercourse.

The system was designed in Ireland where high water tables are a very common problem.

 

Other than for conversion of existing septic tanks, I would struggle to see the benefit to this over a packaged treatment plant? That produce water clean enough to discharge to a watercourse. Unless the irish regs are different..

[saveasteading]

52 minutes ago, crooksey said:

benefit to this over a packaged treatment plant? 

If there isn't a watercourse and the percolation/ water table preclude a soakaway? Also in tight areas where there isn't room for the huge area of soakaway officially required?

Sounds useful if it is readily accepted. Cost?

[Crofter]

7 hours ago, crooksey said:

 

Other than for conversion of existing septic tanks, I would struggle to see the benefit to this over a packaged treatment plant? That produce water clean enough to discharge to a watercourse. Unless the irish regs are different..

From memory, a treatment plant would only allow me to reduce the size of the soakaway. The Puraflo let me almost completely eliminate it.

[Crofter]

6 hours ago, saveasteading said:

 

Sounds useful if it is readily accepted. Cost?

It wasn't particularly cheap. Back in about 2016 I paid around £7k by the time the septic tank and Puraflo was installed.

The company would not do a supply-only deal so it was about the only part of the entire build which had to be handed over to someone else.

[Dunc]

On 08/09/2023 at 16:22, saveasteading said:

If there isn't a watercourse and the percolation/ water table preclude a soakaway? Also in tight areas where there isn't room for the huge area of soakaway officially required?

Sounds useful if it is readily accepted. Cost?

For me this is the key point: if one installs a tertirary treatment such as the puraflo (they use coconut fibre now that extraction of peat is not considered environmentally sound) where would its outflow go in the situation where the ground is too wet for an infiltration field? Still have to be piped to a watercourse or can it drain onto an above ground surface?

[Crofter]

35 minutes ago, Dunc said:

For me this is the key point: if one installs a tertirary treatment such as the puraflo (they use coconut fibre now that extraction of peat is not considered environmentally sound) where would its outflow go in the situation where the ground is too wet for an infiltration field? Still have to be piped to a watercourse or can it drain onto an above ground surface?

I think the idea is that you have a gravel hardstanding and sit the Puraflo on that. But you'd really have to start talking to SEPA.

[saveasteading]

1 hour ago, Dunc said:

For me this is the key point: if one installs a tertirary treatment such as the puraflo (they use coconut fibre now that extraction of peat is not considered environmentally sound) where would its outflow go in the situation where the ground is too wet for an infiltration field? Still have to be piped to a watercourse or can it drain onto an above ground surface?

At such a cost it should be clean, and they should have documentation to prove it ca be disposed of with rainwater.

[crooksey]

On 08/09/2023 at 16:22, saveasteading said:

If there isn't a watercourse and the percolation/ water table preclude a soakaway? Also in tight areas where there isn't room for the huge area of soakaway officially required?

Sounds useful if it is readily accepted. Cost?

 

Puraflow can be a stand alone unit, what I meant was, why not have a PTP then a puraflow, as opposed to a septic tank first.

[Crofter]

6 hours ago, crooksey said:

 

Puraflow can be a stand alone unit, what I meant was, why not have a PTP then a puraflow, as opposed to a septic tank first.

I don't think there's any reason not to, other than the extra cost.

[saveasteading]

7 hours ago, crooksey said:

why not have a PTP then a puraflow, as opposed to a septic tank first.

This is what I have been assuming all along, rightly or wrongly. 

I can't see any justification for using a septic tank if a treatment plant is feasible.

[markocosic]

Pile of poo always an option - US version of the puraflow?

 

(sewage treatment mound)

 

https://www.epa.gov/septic/types-septic-systems

https://groundstone.ca/2018/06/mound-septic-systems/

[diarmidR]

On 08/09/2023 at 23:20, Crofter said:

From memory, a treatment plant would only allow me to reduce the size of the soakaway. The Puraflo let me almost completely eliminate it.

I'm confused about this. For PP, our draughtsman specified a septic tank + Puraflo discharging to a small stream. He doubted the effeciveness of a soakaway and he was right as the percolation was very slow.

 

As the Puraflo is fairly expensive I emailed SEPA to check if an aeration treatment plant could be used instead of the above. The person I spoke to advised me that I should have the PuraFlo plus a partial soakaway of 10m2 with overflow. I'm not sure if this is because they also thought the watercourse I would be discharging to would have too small a flow.

 

I can't find any documentation of this sort of thing online - can anyone help? I feel like the partial soakaway will add nothing but cost and bogginess.

 

Ta, D

[ProDave]

14 minutes ago, diarmidR said:

As the Puraflo is fairly expensive I emailed SEPA to check if an aeration treatment plant could be used instead of the above. The person I spoke to advised me that I should have the PuraFlo plus a partial soakaway of 10m2 with overflow. I'm not sure if this is because they also thought the watercourse I would be discharging to would have too small a flow.

SEPA like a partial soakaway, that is what we have.  it means in the summer, when the ground is able to absorb some water, then less goes into the burn.

[diarmidR]

Thanks Dave, that makes a lot of sense.

[saveasteading]

43 minutes ago, ProDave said:

in the summer, when the ground is able to absorb some water, then less goes into the burn.

That is unusually pragmatic,  good sense.

Also, after a dry spell the first 'flush' for perhaps a week will all rest in the soakaway for a while. as the ground either gets wet again or not.

 

BUT

I've just looked at the Puraflo website.

Firstly using peat is sustainable??

More importantly I can't see why anyone should need one*.  A product in search of a need.

The output from a  modern treatment tank is close to clean. The percolation field or soakaway is to let it soak away, not clean it further, although it will do that too.. 

Water that has gone through a secondary or tertiary treatment plant is no less in volume, so still needs the same soakaway or stream.

Or am i missing something?

 

* to be fair, this could be added to an existing septic tank instead of replacing it, but so could a treatment tank.

[ProDave]

Building regs in Scotland at least allow you to have about 20% less area of soakaway for a treatment plant vs a septic tank.  Is that because they expect the soakaway from a ST to degrade and get clogged?

 

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 and said it would need the same soakaway area determined by conventional means, which is why they rejected it for us.

[joe90]

Well with my treatment plant I discharged to a ditch that was dry a couple of months a year and the pipe (10m) to the ditch was a “rumble drain” which is a partial drain, I.e. perforated pipe in a stone filled trench to the outlet in the ditch.