Recommendation for someone to advise on new sewage connection/septic tank

[hellopaul]

Hello,

I'm wondering if anyone on here can recommend anyone in Suffolk (my site is near Bury St. Edmunds) who could take a look at the potential sewage setup for my house. My issue is this:

When I bought the site, I was told there is a mains sewer in the road, about 30m from the property (it's a barn conversion). But it turns out this is a rising main, therefore pressurised and impossible to tap into. Anglian Water does not seem to be prepared to send someone out to look at the area/site and give advice.

(Uneducated assumptions and a fair amount of amateur guesswork ahead! Forgive my lack of sewagey knowledge...)

So the next nearest mains option would entail a ~90m run, into a manhole whose 'depth to invert' is 1.55m. The site is very flat. If I used 150mm pipe, I'm assuming I could get away with a 1:80 fall (1.125m fall over 90m), but it'd mean I'd be discharging very low down in the manhole, which I presume would risk the foul water flowing through the manhole backing up my sewage pipe. Is that correct? If that is correct, I assume my solution would be one of these expensive-sounding options:

1. Install a pump between my property so it can flow happily to the manhole, with all the installation, running and maintenance costs that this would create.
2. Install a septic tank and drainage field: I have read guides on how to calculate how large a drainage field needs to be (depending on the soil's percolation value and how many people will be using the house) but without knowing the percolation value, I can't even make a guess. If we assume the percolation value is fairly average (the soil is not clay, it's quite nice), could anyone here give me an idea on what the drainage field size is likely to be for a 4-bed, 3-toilet house?
3. Install a sewage treatment plant: Presumably the only reason I'd need to do this is if I don't have sufficient space for a drainage field for a septic tank? (I'm also assuming that Building Control can't arbitrarily insist on this instead of a septic tank...). Obviously this would have higher installation, running and maintenance costs than a simple septic tank.

So if anyone can give me some advice or knows someone/a company who would be interested in looking at this/doing the work, then please let me know!

 

Thanks in advance for any help.

 

- Paul

[JohnMo]

Not sure in England but is Scotland septic tanks are outlawed, you have to use a treatment tank.

 

You simplest cheapest may be a pumped solution to the main. Not sure you would have any maintenance, a decent quality pump should last for years.

 

You just need to watch what fats you chuck down the drain, and other stuff that should not go in a drain, like female monthly products, face wipes baby wipes etc, as these clog the pump.

[Mr Punter]

You can go to 1:150 with a 150mm pipe.  It needs to be spot on - not just chucked in by a gibbon.

 

Whose land is the 90m dig?  Is it verge or road?

 

Given the option mains gravity drainage is a clear winner.

[Wumpus]

I think you’ll find that a sewage treatment plant will still need a drainage field. 
We have just put our drainage field in. It has 3 rows of slotted pipe giving a total of 34m to look after 11 people (it s shared with our neighbours). Our soil is pretty average I would say.

 

you can do your own percolation test, it’s just a 300x300mm cube dug down into the soil and record the time for the water to disappear into the hole. Do this 3 times. You need the time from 75% to 25%, not full to empty.

[joe90]

4 minutes ago, Wumpus said:

think you’ll find that a sewage treatment plant will still need a drainage field. 

Or drain to a ditch that’s wet some of the year (depending on type, mine is a vortex and is allowed to do this). And it’s a lot less work that a leach field.

Edited March 25, 2022 by joe90

[Ronan 1]

1 hour ago, joe90 said:

Or drain to a ditch that’s wet some of the year (depending on type, mine is a vortex and is allowed to do this). And it’s a lot less work that a leach field.

Plus1 that's what I'm doing

[Russell griffiths]

A treatment plant will cost you £2500 to buy then fit and build the drain field. So your going to be in to £5000 materials only if you do all the work yourself including the digging. 
I would go for a 90m run to a main sewer all day long. 
remember with the water tread plant you have ongoing electricity cost plus emptying cost. 
I would give my right arm for a main sewage connection. 

[ProDave]

3 hours ago, Wumpus said:

you can do your own percolation test, it’s just a 300x300mm cube dug down into the soil and record the time for the water to disappear into the hole. Do this 3 times. You need the time from 75% to 25%, not full to empty.

Almost.  the 300mm cube is dug at the bottom of usually a 1 metre cube hole, so the actual test hole is 1 metre deep.

 

[saveasteading]

7 hours ago, hellopaul said:

a manhole whose 'depth to invert' is 1.55m.

This is the depth from the cover, so make sure  that your site is not lower than this, every mm is counting with your numbers.

 

Let's assume that the land at your site is the same level. The drain has to go underground and the minimum will be 400mm if you are clever enough with the layout.

that is leaving you with 1.15m, and things are getting tight.

 

If I was your Engineer I think I could show that a 100 pipe can go at that sort of slope, because the volume is small and the building reg slopes are a bit cautious. In fact the smaller pipe might run better over that long distance.

 

It is very much cheaper to do this gravity drain if you can. 90m of pipe from your own 'gathering' manhole, a proper manhole at the connection, which the water company will want to approve, and a couple of intermediate inspection chambers for rodding.

 

you cannot afford to lose any height from the property, so lowering the floor would create an issue, whereas lifting it will help.

 

re treatment tank/ septic/ cess tank:  these terms are much confused.

The building regulations are well written on this subject and I recommend reading several times.

 

My second choice is treatment tank, because it costs much the same as a pump and connections.  (it has to be a big tank in case of failure) , it is all yours and you don't have pay sewage rates.

 

Although it is correct about digging a 1m hole, you can try a hole nearer the surface as a quick guide.

 

 

 

 

[Gus Potter]

31 minutes ago, saveasteading said:

If I was your Engineer I think I could show that a 100 pipe can go at that sort of slope, because the volume is small and the building reg slopes are a bit cautious. In fact the smaller pipe might run better over that long distance.

Very clever! hat off to @saveasteading its almost counter intuitive to use a smaller diameter pipe.

 

Yes I too think you could make this fly with careful control over the laying of the pipe and the odd extra inspection chamber. On a straight run its even more promising.