Sewage soil pipe length?

[Wayneywoo]

Hello, I am pretty new to drainage and hoping the experts on here could help us.

We have a house that is lower than the public sewer, we have ordered a pumping station to move the sewage to the main sewer.

At the moment there is an old fossa that just leaks into the soil around the tank, it has also a cracked concrete top and no access cover hence why we are going down the pumping to main sewer route.

We have a large buildings that we are thinking of converting later on so would like to utilise the pumping station for both buildings, to do this I would need to run a 110mm soil pipe or larger if you think I should. This pipe would serve two toilets and two bathrooms plus a kitchen.

My question is what is the maximum length I can run the main pipe from the house to the pumping station, the distance I'm thinking is around 20meters. I can create a fall but unsure what size pipe to use and what fall that size pipe should be.

Many thanks for any help with this.

Wayne

 

[Hugh Jaleak]

110mm will happily cope with a number of dwellings, so will be more than adequate for your proposal. The Pumping station though, needs to be sized with the extra capacity in mind. Should it break down, power failure etc, then it needs to be able to store enough effluent to prevent an overflow/pollution until such a time it can be repaired, or a tanker engaged to empty it.

Distance, as long as you like, provided it's on the correct fall, (1:40 is recommended for 4"/110mm, although you can drop as low as 1:100 if absolutely necessary), with a maximum run of 100m between chambers.

 

[Wayneywoo]

Thank you so much Hugh, a very straight understandable answer, Google doesn't help there's too much information for me to take in.

Yes we sized the pumping station at 1200 litres with dual pumps in case one ever failed. We also have farmers on standby.

Yes that's great news, 110mm it is then, I was going to fit a vent at the top of the soil pipe, would you recommend this or just an air admittance valve?

We would probably have to dig deep to attain 1:40 but it's achievable.

 

[Hugh Jaleak]

Vent at the head of the run, and if there's a ventilation option at the Pump Station end, go for an AAV there. Simply put, air passing over the vent will draw air in at the lower level via the AAV and ventilate the system.

Don't go any steeper than 1:40 or you may have problems, the water may run away, leaving solids behind, which will soon cause an issue. Works out at 500mm over the 20 metres, that's the maximum you'd need. Can reduce it slightly if necessary on a straight run, with modern smooth bore pipework.

 

[Hugh Jaleak]

Meant to add, are you UK based? Just bear in mind it is illegal for anyone other than a registered contractor to empty a septic tank or similar, the Environment Agency have a history of prosecuting offenders.

 

[Wayneywoo]

Yes thank you for clarifying the vent options, so it's better to vent at the pumping station?

No we are in Portugal, I checked at the camara (council) who came out to price up the connection to the public sewer. They will be fitting an inspection pit for the HDPE pipe from the pumping station to discharge into then gravity to the public sewer. Price is €250.

They said I should install everything then they will come out to do their bit. I guess they like to check that it flows into the sewer ok. I guess there happy that it will be another leaking fossa off the list, there are so many here in Portugal.

 

[Wayneywoo]

Oh, no not really using a farmer. We pay €2 a month for sewage which covers emptying of fossas.

 

[Hugh Jaleak]

Yes thank you for clarifying the vent options, so it's better to vent at the pumping station?

No, fit an open to atmosphere vent at the top (building) end, assuming you'll be taking a stack up to eaves level, where any odour will not offend anyone. Then if there is a connection at the Pumping Station end, I'd fit an AAV there. Allow air in at the lower point, through the system and vent to atmosphere at the top end where it wont cause a nuisance.

 

[Wayneywoo]

Understood, thank you so much for your help and advice. Wayne.