Treatment plant installation

[deuce22]

Hi.

 

I am looking for some advice on finishing the installation of my treatment plant. I was planning on buying a condor, but was told by the company that the mould had been damaged and it would take 6 to 12 weeks before they started manufacturing again. I was advised by the BCO to get a Marsh, which I was a bit apprehensive about, as it comes in two pieces. I went ahead with it and also had to buy a 1m extension.

 

I had major problems with the initial pour and the plant lifted around 350mm from it's original position. Due to this, I had to install a pumping station, so that the drainage for my garage (which is around 600mm below the house) could be pumped into the plant. I did every thing that both the instructions and rep stated, but it still floated when pouring concrete. The problem is, you can only fill the tank up to the join (halfway) as it will put pressure on it. When the driver for the concrete company looked inside he said it wasn't full enough and he knew what would happen as he does about 5 a week. Exactly what he said is what happened. I've moved on from this now, but have no confidence in anybody from Marsh as they've been really unhelpful. They actually tried to sell me another treatment plant.

 

I was told by the rep that I needed to concrete the whole plant all the way to the top. As I've had to dig down 3m, the ground had to be lowered all around as it would have just fallen in on itself. Due to this large open area around the plant, it would cost to much to just pour concrete in until it was full. The only way I can concrete the whole thing is to shutter it in stages, but this is going to cost a lot more in concrete.

 

What I'm trying to find out is, as the plant is now anchored with about 20 tonne of concrete, do I need more. Can I not just fill around the rest with gravel? It does state that in low water table level areas you can back fill with gravel. I don't know what the water table level is here, but there is a lot of surface water as it is on the side of a mountain.

 

Thanks for any help.

[ProDave]

Pump out the water and at least get the concrete over the main "barrel" of the plant.

 

TIP for any other readers, while you are right you cannot fill it with water all the way to start with, you should keep adding more water as the concrete is poured so the water level inside is as high as the concrete outside as you pour.

[saveasteading]

Sorry to hear of your problems.

I think we know where the water table is! It is at the surface of your puddle, and the tank of course wants to float.

When you pump it out does it fill again from the bank?

The water table may rise when the hole is filled and in winter.

 

Placing these tanks is difficult, and as ProDave says, it requires patient pouring in stages.

 

That is a very big hole, and of course you don't want to fill it with concrete. This can be avoided by putting a shutter round the tank to keep the concrete to a reasonable thickness. If you have spare boards or metal cladding it can be left in sacrificially. Then you can backfill in gravel or earth, either concurrently or later.

You can do the same shutter thing with gravel/earth.

OR you could possibly use a very dry and stony concrete mix, and some shuttering, and shovel it in to place. That would also need some continuity of pour and perhaps bars to link it to the base.

 

That right hand pipe looks odd. presumably that is a temporary arrangement.

BTW  I go to your supplier as my first choice , because I have found the product and technical advice to be so good, and have also used 2 other bigger names.

 

Once the tank is in operation it is full of water and should be stable along with the concrete ballast, and a lot of backfill above. You then must be cautious if ever pumping it out completely, so best not to.

 

If you need any more advice it might be best to tell us what went wrong, and what the current stage of construction is/ a photo of the drained situation.  Do this privately if you prefer.

Best not to slag any company on here as it is all searchable on google.

 

[deuce22]

32 minutes ago, ProDave said:

Pump out the water and at least get the concrete over the main "barrel" of the plant.

 

TIP for any other readers, while you are right you cannot fill it with water all the way to start with, you should keep adding more water as the concrete is poured so the water level inside is as high as the concrete outside as you pour.

Yes, I was aware of the adding of water as you're pouring, but it wouldn't have made a difference. I filled it with water to the half way point (used a laser level to get it accurate), but it started lifting about 300mm down from that level. I had to use the bucket of an excavator to stop it rolling over and decided to stop with the concrete about 100mm below the water level. I then had them come back out and added another 2.5m3.

The concrete driver has only seen plants that are in 1 piece and he said they are always filled. Is he right, can you fill the 1 piece plants to the top?

[nod]

I’d no experience of installing a TP

I sat it in two cube of concrete with a small amount of water in the tank Then left the hose running till the following morning 

I intend doing the same on our next one

So many seller say there TPS can be sat in pea gravel 

[deuce22]

20 hours ago, saveasteading said:

Sorry to hear of your problems.

I think we know where the water table is! It is at the surface of your puddle, and the tank of course wants to float.

When you pump it out does it fill again from the bank?

The water table may rise when the hole is filled and in winter.

 

Placing these tanks is difficult, and as ProDave says, it requires patient pouring in stages.

 

That is a very big hole, and of course you don't want to fill it with concrete. This can be avoided by putting a shutter round the tank to keep the concrete to a reasonable thickness. If you have spare boards or metal cladding it can be left in sacrificially. Then you can backfill in gravel or earth, either concurrently or later.

You can do the same shutter thing with gravel/earth.

OR you could possibly use a very dry and stony concrete mix, and some shuttering, and shovel it in to place. That would also need some continuity of pour and perhaps bars to link it to the base.

 

That right hand pipe looks odd. presumably that is a temporary arrangement.

BTW  I go to your supplier as my first choice , because I have found the product and technical advice to be so good, and have also used 2 other bigger names.

 

Once the tank is in operation it is full of water and should be stable along with the concrete ballast, and a lot of backfill above. You then must be cautious if ever pumping it out completely, so best not to.

 

If you need any more advice it might be best to tell us what went wrong, and what the current stage of construction is/ a photo of the drained situation.  Do this privately if you prefer.

Best not to slag any company on here as it is all searchable on google.

 

That puddle is between 50 and 100mm deep and is on top of 7m3 of the concrete pour. The water is running off the bank, so I cannot judge where the water table is. Ive excavated quite a lot on the site and it always fills with water running in from above. 

 

It states that it only needs 200mm thickness around the plant, so shuttering seems like the only way. That right hand pipe needs to be connected to the pipe with the blue hose going into it.

 

Why do I need to be cautious when emptying it now? I assumed that as it's been concreted in and set it can now be emptied and will not move at all.

 

I am not trying to slag off this company, just give feedback from my experience with them. I was told by a local groundwork to buy a concrete plant, but as it was £5500, I thought I would save a bit by getting a plastic/fibreglass one. With the extra concrete I've now had to buy and also the pumping station (which I didn't originally need), I'm not going to be far off that figure.

 

I now know what I need to do and the clarification from you guys have confirmed what I was thinking. Thanks very much for your help.

[ProDave]

14 minutes ago, deuce22 said:

Why do I need to be cautious when emptying it now? I assumed that as it's been concreted in and set it can now be emptied and will not move at all.

Unless the concrete goes over the top there is nothing really holding it down.  By my estimate the concrete is not up to the half way point of the "cylinder"

14 minutes ago, deuce22 said:

That right hand pipe needs to be connected to the pipe with the blue hose going into it.

And how do you propose to rod it if it blocks?  That's going to need at least 2 very deep inspection chambers.

[Ronan 1]

52 minutes ago, ProDave said:

1 hour ago, deuce22 said:

That right hand pipe needs to be connected to the pipe with the blue hose going into it.

And how do you propose to rod it if it blocks?  That's going to need at least 2 very deep inspection chambers.

Dave is right, it looks to me like you are burying some future problems deep !! 

With the orientation on your incoming and outgoing pipework that tank should have been turned 90 degrees which would have made it somewhat easier.

 

You will need to fill over the barrell of the tank with concrete, I'd use a damp leanmix and any half decent driver should be able to bank up the muck to act as a shutter as he's going along.

 

That hole is  nasty looking now but it is nothing to how bad the hole will be IF you have to go back and try and rectify things at a later stage.

 

Get your GW and Machine driver by the scruff and get them to sort it out right for you whike the hole is still open.

[TonyT]

Get some stainless steel rope and wrap it around the lifting eyes and then resin this to the concrete, this will help prevent uplift while you add more mass.

[deuce22]

1 hour ago, ProDave said:

Unless the concrete goes over the top there is nothing really holding it down.  By my estimate the concrete is not up to the half way point of the "cylinder"

And how do you propose to rod it if it blocks?  That's going to need at least 2 very deep inspection chambers.

The concrete is around 200mm above the join, so I can't see it lifting as it covers the lip of the joint. I will do as you said though and shutter around the main body and completely encase it all.

 

The image is exactly what I have done. I was told that there is no need for an inspection chamber on the outlet drainage pipe as it is just water that is going through. Would you suggest putting one between the pumping station and plant.

 

Thanks.

[joe90]

If the water is running off the surface rather than bubbling up from beneath then your water table is low. From my reading on this having installed my own STP was that holing the tank is only required if the water table is high. I was just going to say similar to @TonyT above, chain or cable over the unit fixed to the concrete would suffice IMO.

Edited August 8, 2021 by joe90

[ProDave]

What do building control say about this?

 

Up here there must be an inspection chamber wherever there is a change of direction of the run.  You need a lot more inspection chambers.

[Dave Jones]

30 minutes ago, ProDave said:

What do building control say about this?

 

Up here there must be an inspection chamber wherever there is a change of direction of the run.  You need a lot more inspection chambers.

 

this is correct, recipe for disaster if not done correctly.

Edited August 8, 2021 by Dave Jones

[deuce22]

43 minutes ago, Dave Jones said:

 

this is correct, recipe for disaster if not done correctly.

Do you need an inspection chamber on a 45 degree bend? I was told it was only on a 90 degree bend.

 

The 2 joints that are used directly from the outlet are long radius bends and I was told to use these as it was only water (no solids) coming from the outlet. I do want to get this done properly as I know it will be a nightmare once every thing is back filled.

 

Thanks.

[Dave Jones]

you could straighten the run between the pumping station and tank and get away with a single chamber and do the same with the outflow. They are cheap and easy to install now and come the unplanned blockage you will be very glad you added them.

[deuce22]

Ok, thanks.

 

I'll add some small inspection chambers where needed.

[saveasteading]

6 hours ago, deuce22 said:

That puddle is between 50 and 100mm deep.

Good. so the water table is not high, at least at the moment. 

On a steep slope the water table will tend to follow the slope.

However, I would not be tempted to use gravel surround, regardless of the water table, as water fill flow into the gravel from the slope above.

 

and is on top of 7m3 of the concrete pour. 

the tank could usefully be tied down to this very great mass, as described above. You need very sturdy hooks into the base  (resin anchor?) , then the cables through the lifting eyes, and take the slack out.

 

Why do I need to be cautious when emptying it now? 

If the tank was emptied below the level of any ground-water. at any stage in its life, it would float. If you tie it down and surround with concrete you don't have to worry.

Actually, you will have  a lot of earth over it which will weight it down.

 

'I am not trying to slag off this company, just give feedback from my experience with them.  

Ok but it read otherwise to me. I cant see where they are at any fault from your account.

 

 

6 hours ago, deuce22 said:

I filled it with water to the half way point (used a laser level to get it accurate), but it started lifting about 300mm down from that level.

That seems impossible to me unless the concrete flew rapidly underneath* or was agitated/vibrated. That could be caused by the concrete supplier or groundworker. ...and they kept on pouring??   Anyway, nothing to be done now.

*pouring down a chute from a considerable height?

 

The other comments about pipe runs and inspection chambers are correct. Best read this for your own satisfaction, then to achieve approval.  https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/442889/BR_PDF_AD_H_2015.pdf 

I can't cut and paste from it but see clause 2.13.

The rules have been relaxed. It used to require a chamber at every change of direction horizontally or vertically. Now it says to avoid too many access points, but must still use them at changes of gradient.

There is more advice at 2.19 and 2.20.

This is good advice because chambers themselves can restrict the flow. However, you must minimise bends and keep them large radius.  As others say, you can improve this design.

 

1.43 says you need a testing chamber. I think that could be anywhere down  the line. Marsh sell them but advised me that they are easy to build on site.

 

I am concerned that a building inspector might interpret the need for access and avoiding changes of direction differently, as it is vague At some stage I suggest you bite the bullet and get it approved before building and burying.

I think I would own up to the issues, then stress that this will be cleaned fluid, free from solids, and in small quantities.

 

Another worry might be the pump. What happens if it fails? If it is approved for the job and has storage then fair enough.

 

I have a practical tip for later. However well the groundworker installs the pipes, there is a strong chance of a local error that slows the flow and causes a blockage. Using a laser level does not make it right.

So after they have gone home, so that they are not offended or distract you, lay a golf or snooker ball at the top of the run. Give a tiny push if necessary. If it runs al the way you should be ok.

If there is a problem, then this test is easy to understand and to be accepted when you show the groundworker.

 

Don't hesitate to come back to the forum with your proposals.

[deuce22]

Thanks very much for that PDF, I'll take a good look through it.

 

The setup at the moment is, I've got one drainage pipe exiting the garage and going directly into a 450l pumping station. I needed this because the plant lifted when pouring concrete. However, as the garage is lower than the house, I do not need the drainage for the house to go into a pumping station. It joins onto a y connection about a metre past the join between the 60mm pump station pipe and 110mm underground pipe.

The fall for the house drainage pipe is fine on it's own, but as I've got the pump station installed it will also pump what is coming from the house further down the line. I have tried to keep all connections as either a long radius bend or 30 and 45 degree bends. I was told to use these as they can be rodded easier than a standard 90 degree bend.

I'm thinking of putting a chamber within the first few metres of the outlet, but will now change this to a testing chamber. I'm also thinking of putting another one in place of the y connection, so I will now have 1 just before and 1 just after.

 

I've connected a non return valve onto the 110mm pipe that enters the pump station. If the sewage pump fails and the tank fills nothing will come back through the pipe into the garage. I will then have to renew the pump. As the garage will be temporary accommodation for us whilst i'm building the house, it will have a small amount of use after we move into the house.

[saveasteading]

Sorry: I am confused.

The drainage you show from the garage: is this a toilet?

For that  you wouldn't need a big pump, just a saniflo.

The house drainage appears to go direct to the treatment tank, but you mention that the pump takes house water, from 'further down the line'. Why?

[deuce22]

The garage has a shower room downstairs and a 1 bed flat above, so that is why I went down the pump station route.

 

The drainage for the house links into the drainage coming from the pump station about 1m after the connection between the 60mm and 110mm pipes. It is on a Y connection. As the house is higher than the garage it does not need any assistance from the pump.

 

I spoke with somebody today about the drainage and they said a similar thing about inspection chamber slowing the flow and potentially causing problems. They've told me to put a rodding point on the run coming from the house, a chamber on the run between the pump station and plant and a testing chamber on the 45 degree bend on the outlet pipe.

 

The reason it was install this way is, that it was better to have more of the bends on the outlet pipe as it is less likely to block with only water running through. If it was turned 90 degrees there would have been more bends on the inlet pipe.

[deuce22]

Hi.

 

Sorry to drag this on, but I just want to make sure things are being done correctly. I've spoken with the guy today and he has said the following.

 

The concrete is used to anchor the plant in, not to protect it as if the ground was dry there is no need for concrete around it at all. The concrete is 200mm below the inlet pipe, so it has reached a level where it is impossible for that to lift. It couldn't even be pulled out now with machinery, it would just be ripped apart. 

As there is a pump station within 6m of the plant, it is highly unlikely that there would be a blockage within that run, but if I want he will put a chamber in where the house drainage connects.

He has used long radius bends for the outlet as there is no need for a chamber due to it only being water discharged. Again, he will put a chamber on one of those bends if I want as high flex rods will be able to rod the other bend.

The final outlet into the watercourse will be fitted with a non return valve and go directly into an open ditch/stream. There is no need for a test chamber as samples can be taken from this open end.

 

He is now going to back fill around the rest of the plant with hardcore/tarmac planings as you need a material that keeps as much surface water out rather than using a free flowing gravel. He said it is the same when I come to waterproof the house. I know the waterproofing company has told me to compact the earth backfill in layers, on top of the land drain/stone/geotextile, to reduce as much water actually getting in.

 

Does all this seem reasonable?

 

Thanks.

[ProDave]

Re the position of inspection chambers.

 

Get him to agree he will do what building control deem necessary.  Get him to install ALL the chambers he thinks necessary, then BEFORE it is covered over get building control to inspect it.  If they say they want more, he must fit more.

 

I would still want more concrete over the top personally.

[deuce22]

9 minutes ago, ProDave said:

Re the position of inspection chambers.

 

Get him to agree he will do what building control deem necessary.  Get him to install ALL the chambers he thinks necessary, then BEFORE it is covered over get building control to inspect it.  If they say they want more, he must fit more.

 

I would still want more concrete over the top personally.

Ok. I'll do just that.

 

Can you tell me why you'd want more over the top. I'd like to have a reason for him. I did say it needed covering completely, but he had an answer for not doing it.

 

Thanks.