Install of Waste Treatment Plant

[Gaum]

Foundations are on hold due to terrible weather so I’m moving on to the waste treatment plant so I can eventually get the caravan hooked up and live on site. Well, after treatment plant, soak away and drainage pipes are laid that is;

Now I may be over thinking this but I can’t seem to make sense of the final depths required; what depth should I be siting the treatment plant (it’s a Graf one2clean 7 by the way)?

Please correct me if I’m wrong.

 

Total fall of Pipe;

From the furthest sewage outlet from the house, following the line of the drains on the plan to the plant inlet is 48m. In my head the bottom of the furthest sewage outlet as it exits the foundations will be classed as Zero depth (200mm below finished ground) so am I correct in calculating the following?

The fall for 100mm sewage pipe should be between 1:80 & 1:40 over the 48m, so depth of inlet to the treatment plant will be between 0.6m & 1.2m below Zero. (0.8 & 1.4 below finished ground).

 

Depth of Treatment Plant;

If I opt for the shallowest fall at .08m below ground the top of the plant is only 460mm above inlet so it’ll be below ground. Applying a neck extension gives me another 330mm according to the diagram, so I have 790mm above inlet, 10mm below ground. Are the tolerances normally this tight or am I missing something?

 

 

[Crofter]

You really don't want the plant to be sitting in a local depression- surface water will end up running into it which is not good.

This can definitely be a problem on flat sites (wasn't a problem for me!)

Can you move the treatment plant closer to the house?

[ProDave]

Your sums seem right. It looks like you will need to use a neck extension on the plant.  It also of course means the outlet will be that much deeper. Will that be okay for your soakaway or whateverdrainage  arrangement you have? if not you may need a pumped outlet version.

Why is the drain run so long? Building regs only need the plant to be 5 metres from a building (That's what the Scottish regs say, it may be different in other parts) so could the treatment plant go closer to the house?

Also be aware that a lot of the manufacturers stipulate that if a neck extension is used, the entire treatment plant plus neck exrtension must be encased in concrete.

If the weather is too bad for foundations, is it really okay for digging the deep hole you need for the treatment plant?  I had to chose the time carefully as we have a high water table. Even waiting for a long dry spell, the hole started filling with water straight away.

Another thought:

Your chosen plant seems to be a "low invert" type?  the one I used, a Conder ASP6, has an inlet invert depth of 760mm so would only need the small neck extension.

Could a re visit of which plant you are using, together with trying to shorten the drain run, give a solution that doesn't need a neck extension? The Conder is very close to achieving that.

One last thought, I am on a sloping site, so I am building up my ground levels from the original levels when I landscape the plot. In effect, the drainage slope and the invert depth of the treatment plant has set one of the "datum" points for how much I raise the ground level at that particular point and from that, the rest of the landscaping levels flow.

[Gaum]

1 hour ago, Crofter said:

You really don't want the plant to be sitting in a local depression- surface water will end up running into it which is not good.

This can definitely be a problem on flat sites (wasn't a problem for me!)

Can you move the treatment plant closer to the house?

 

1 hour ago, ProDave said:

Your sums seem right. It looks like you will need to use a neck extension on the plant.  It also of course means the outlet will be that much deeper. Will that be okay for your soakaway or whatever draninage arrangement you have? if not you may need a pumped outlet version.

Why is the drain run so long? Building regs only need the plant to be 5 metres from a building (That's what the Scottish regs say, it may be different in other parts) so could the treatment plant go closer to the house?

Also be aware that a lot of the manufacturers stipulate that if a neck extension is used, the entire treatment plant plus neck exrtension must be encased in concrete.

If the weather is to bad for foundations, is it really okay for diging the deep hole you need for the treatment plant?  I had to chose the time carefully as we have a high water table. Even waiting for a long dry spell, the hole started filling with water straight away.

Thanks for the feedback but I didn't explain the pipe run very well; the plant will be about 6m from the house to the southeast. The run I was describing was from the bedroom ensuite on the west side. The pipe then runs north and East around the house picking up the outlets from the bathroom, wc etc to the plant. 

The drain to a burn about half a mile away comes into the plot at 1.7m down so plenty of leeway for the soakaway and even the depth of the plant.

As for the type of plant I've already got it onsite. It just seemed deep for the pipe run but if the sums are right I'll just have to bury the plant and buy another extension to make sure I'm clear of the ground. The manufacturers' rep reckons there's no concrete required even as a base as the ground is very hard at the depth.

You are right about digging in this weather but it was sunny when I started honest and the water table's not an issue here. I'm more worried about the hole collapsing with all this rain. 

A quick bite to eat then I'm off down to the plot just now to see what the damage is! I think I'll be needing my wellies.

[Gaum]

Does the font in my post look funny or is it just my phone screen?

[Crofter]

2 minutes ago, Gaum said:

Does the font in my post look funny or is it just my phone screen?

It was written in different sizes. Fixed it for you now! Don't worry, no charge for that

[Gaum]

1 hour ago, Crofter said:

It was written in different sizes. Fixed it for you now! Don't worry, no charge for that

Thanks Crofter you're a Gent.

[Gaum]

Crofter it must be my phone. I was halfway posting about my visit to the plot and pressed delete a few times then it froze. Do me a favour and delete the unnecessary. Unless I can do it?

[Gaum]

Well before breaking the forum I went down to the plot and I agree with Dave that's it's not a good idea to dig a hole when it's going to rain. I've now got a hole that was the right size and depth but it's now a bit longer and wider than I left it yesterday! So I hammered in some pegs, about 10ft all round and wrapped it in barrier tape, moved the digger out of the way just in case and drove off not looking in my mirror once. Hopefully if this weather abates I'll get back to it and it'll not need too much clearing and backfill.

Foundations are looking like a big brown pond, must be 4" deep at least so that'll take some drying. Heavy clay just won't let it drain away I'll have to dig some trenches to help it on its way.

[ProDave]

When digging my foundations this time last year (it was wet then as well) I used a submirsible electric dirty water pump to pump the water out of the trenches.  For all the complaints I have about our lousy soil, none of the trenches ever collapsed.

[Jeremy Harris]

The concrete around a treatment plant is to anchor it and stop it floating out of the ground, not to support it, so hard ground doesn't negate the need for a ground anchor if the area around the treatment plant is likely to get saturated with water.  We fitted a concrete anchor ring around ours to stop it floating up, as per the manufacturers recommendation.

They can (and do) float out of the ground, as when only partially full (as would be the case with a long neck extension) there can be a few tonnes of buoyancy, and that can easily float a tank or treatment plant out of the ground.  I have some personal experience of this, as we buried a Klargester "onion" septic tank on a farm in Cornwall years ago.  We just put pea shingle around the thing and backfilled the hole.  A week later it had broken free and was sitting on top of the field, just like a damned great orange mole..............

[Gaum]

Hi JSH Thanks for the advice on the concrete base and anchoring the tank. I'll double check with the supplier as they normally do the installs in this area. Nothing much going to happen on the tank front now for the next few weeks as I've been called away with work. Just when the weather's due to dry up! Hopefully get the builder onsite to complete the foundations while I'm away though. 

And just found out that the original neck extends to 340mm so shouldn't need an additional extension. 

[Gone West]

Different sewage treatment plants use different methods of installation. Mine for instance doesn't use concrete to hold it down. It has an old 2'x2' stone slab which the base sits on. It has four galvanised angle irons driven horizontally into the sides of the hole which it is strapped to with galvanised chains to prevent lift. It is back filled with sub-base. I chose it because it was a relatively easy DIY.

[joe90]

15 hours ago, PeterStarck said:

Different sewage treatment plants use different methods of installation. Mine for instance doesn't use concrete to hold it down. It has an old 2'x2' stone slab which the base sits on. It has four galvanised angle irons driven horizontally into the sides of the hole which it is strapped to with galvanised chains to prevent lift. It is back filled with sub-base. I chose it because it was a relatively easy DIY.

Which tank did you use Peter?

[Jeremy Harris]

 

17 hours ago, PeterStarck said:

Different sewage treatment plants use different methods of installation. Mine for instance doesn't use concrete to hold it down. It has an old 2'x2' stone slab which the base sits on. It has four galvanised angle irons driven horizontally into the sides of the hole which it is strapped to with galvanised chains to prevent lift. It is back filled with sub-base. I chose it because it was a relatively easy DIY.

Ours came with the option of a similar ground anchor kit, as an extra.  Form the description it sounds very like the one you describe, galvanised angle iron and chains:

 

Because our unit was going to have it's lower 1/3rd below the local water table I was a bit concerned about the possibility of corrosion (and I may be paranoid, but having witnessed a Klargester "onion" float out of a field I wasn't taking any chances!).  When I spoke to the manufacturer they said they had moulded in lugs that could be embedded in a concrete ring anchor, as an alternative to using the anchor kit.  It was a bit fiddly, as we had to hold the tank up in the air with a digger as a crane, whilst barrowing in concrete around the narrow slot around the tank, then lowering to its final resting place, pumping water into it to get it to sit at exactly the right level.  There was a layer of gravel under the concrete that the pointed bit of the tank base was resting in, with the concrete ring above this.

[ProDave]

The issue of "anchoring down" the tank was one thing that made me chose the Conder.

It has built in legs and the ring around the bottom. So it sits unaided in the hole while you pour enough concrete to encase that ring to anchor it down.

Some of tha alternatives that had various anchor kits, seem to involve someone going down into the hole to fix parts of the anchor kit, which frankly sounds a VERY dangerous exercise.

[Gone West]

11 hours ago, joe90 said:

Which tank did you use Peter?

I used the WPL Diamond DMS2.

[Gone West]

My neighbour is having a bungalow built next door. The builders installed a Klargester BioFicient, with a central anchor. They filled it with water and concreted it in. They pumped it out the next day and it popped out of the ground, the water table can be high here! After lots of digging out and then back filling completely with concrete they got a tank which is not level and can't be moved or adjusted!

[Crofter]

Lot to be said for building a blockwork tank! Except I suppose it might be hard to get approval for it?

[JulianB]

Morning All,

 

Thought I'd resurrection this discussion as I'm about to embark on the installation of our sewage treatment plant. We've opted for a 7 person GRAF one2clean and the supplier has recommended to backfill with pea shingle. The ground is heavy clay, so it is quite difficult to really establish where the water table is as any rainfall tends to just collect and sit in any hole we've dug. The tank will most likely sit a maximum depth of 1.5-2metres below current ground level, and land continues to fall away beyond our back garden. In the fear of the thing shooting out of the ground weeks after I've broken my back installing it, would the general consensus be to fully submerge the tank in concrete? Is the pea shingle route too risky?

[joe90]

For what it costs I would use a  dry concrete mix, peace of mind. We had to do that with ours as our water table is high but spookily when the hole was dug it looked dry but I was not willing to take the risk.

[ProDave]

+1 for concrete.

 

Otherwise when it needs emptying you will be worrying and wondering if you should wait for a long dry spell before you dare empty it.