New drainage connection advice

[d438a1]

Hi there,

I'm in process of running a new drain at front of house for a new upstairs bathroom. I've dug out where it needs to connect to and got a rough idea of what I hope to do now. I've got the building inspector coming at end of week but wanted to check views here first.

As you can see from attachments the connection is very close to the Sewage Treatment plant (STP). The inlet to this is around 1.3m deep where the main line from back of house runs. There is also a separate drain connection that runs alongside this and drops vertically which comes from garage.

Unfortunatley it seems like they have bedded it partly in loose concrete and it's proving hard to easily excavate under the pipe to get an inspection chamber base in. So in the sketch I've shown in the dark colour pipe my proposal instead with an extra rodding point as well (if necessary). The new connection is a straight run about 15 metres and will have an inspection chamber and the main existing drain. also has an inspection chamber about 12 metres away. And the drain from garage also has an inspection chamber about a metre away next to STP.

Also, yes I'm pretty sure the water is ground water and not a massive leak from the STP. I recently moved in to house and had all the drains surveyed and they all seem fine.

So, does my proposal seem ok?

Thanks

[crooksey]

Underground pipes that are not adopted are very rarely queried by building control.

 

You have made provisions for rodding which is good, they will probably just want a pressure test once finished, especially considering the presence of groundwater after such a long dry spell.

[Nickfromwales]

Technically it all looks ok, but I’d be worried about how low your new Y branch is connected and how low the new horizontal pipe run is, as the level of ‘product’ in the STP could rise and come to backfill into that new pipe and settle / block it. I’d want that as high as the existing run.

[ProDave]

21 minutes ago, Nickfromwales said:

Technically it all looks ok, but I’d be worried about how low your new Y branch is connected and how low the new horizontal pipe run is, as the level of ‘product’ in the STP could rise and come to backfill into that new pipe and settle / block it. I’d want that as high as the existing run.

If the level in the STP has got that high then there is something seriously wrong (blocked outlet) and the original VERY low inlet pipe would be completely swamped and blocked long before that.  If that original low level pipe has never given trouble, then the new higher one is not in danger.

[Nickfromwales]

3 hours ago, ProDave said:

If the level in the STP has got that high then there is something seriously wrong (blocked outlet) and the original VERY low inlet pipe would be completely swamped and blocked long before that.  If that original low level pipe has never given trouble, then the new higher one is not in danger.

There’s a lot of gravity to support the lower one, but if the levels of the unfavourable don’t / won’t get up to the new level then rodding access should be enough insurance I guess. 

[Mr Punter]

I don't understand the diagram.  I thought the tank inlet and outlet would normally be towards the top of the tank.

[d438a1]

Thanks all for replies. I only recently moved in, but I did have drain surveys done and everything seems intact. See attached a few photos where you can see the vertical drop and then where it enters STP.

 

I haven't determined exact levels yet, so the branch may be able to go higher. Is it worth considering making the run more like 1 in 50 to get the branch higher?

 

Thanks

[ProDave]

22 minutes ago, Mr Punter said:

I don't understand the diagram.  I thought the tank inlet and outlet would normally be towards the top of the tank.

It is not normally that deep. There must be an extended neck for it to be that deep.

[Nickfromwales]

2 hours ago, Mr Punter said:

I thought the tank inlet and outlet would normally be towards the top of the tank.

Likewise, as the levels in the STP surely would be above the bottom inlet (outlet) as per the pic. The pic doesn't really correlate well and doesn't appear to show the vertically dropping pipe into it?

 

I'll admit to being a bit lost when looking at the photos vs the SketchUp stuff? @d438a1?

[d438a1]

So looking at photos on internet for biodisc, I think the inlet is at the correct height relative to the machinery. It's just set down a lot lower than maybe it ordinarily would be and I guess essentially has another riser (or neck if that's what you meant @ProDave?  on top to get to ground height. I think the reason it's set so low is that the primary drainage comes from back of house and all the way around side. So it's probably a good 30 metre run in total before it gets to STP. Apologies I thought I'd sent a photo of inside orignally. See attached now. Arrow shows the inlet.

Edited Thursday at 15:35 by d438a1