Sewer and Water proximity 1

[tfam]

Most modern civil codes require that sewer and water mains cannot be installed in a common trench, and should have at least 10 feet or more of separation to avoid contamination of the water supply.

example

https://www.cityoffullerton.com/civicax/filebank/blobdload.aspx?blobid=3393

Does anybody know what kind of contamination can occur if they are buried in the same trench, especially if the sewer main is experiencing separation between the 10’ segments( transite pipe) and leaking which occurs at multiple spur connections due to excessive wear or corrosion of the pipe due to ground water/salt water intrusion.

Multiple engineers have stated that the water main cannot be effected because the water is under pressure, but if that is the case then why require the seperation of 10’ feet?

 

[ashtree]

Yes they are correct. But what happens if you have to repair the water main or to install a tapping and the sewer is leaking or damaged. If they are 10feet apart they are also less likely to be damaged when digging up the other main, and less likely to have a connection made onto the wrong main.

The other thing to think about if you are laying a sewer in the same trench as a water main it is likely that the sewer is a force main, otherwise it has to be laid on grade. Therefore you have both pipes under pressure.

Regards
Ashtree
"Any water can be made potable if you filter it through enough money"

 

[PEDARRIN2]

Water mains can be affected since they are typically connected by mechanical or similar joints. Occasionally, there is a water main break and the pipe looses it's pressure. If there is a broken or leaking sewer pipe, contamination can occur.

At other times, there might be a fire event somewhere and the pumper truck flow is such that there is a low (sometimes even less than 0 psig) on the main, which can cause infiltration into the water pipe. Or the municipal system might loose power to their pumps, causing similar low pressures in their piping. This is one of the reasons backflow preventers are required in commercial buildings.

On the building plumbing side, the restrictions are a bit less stringent. The codes allow for the pipe to be in the same trench or less than 10 separation if the sewer pipe is lower than the water pipe and/or the water pipe is sleeved.

 

[bimr]

Multiple engineers have stated that the water main cannot be effected because the water is under pressure, but if that is the case then why require the seperation of 10’ feet?

These are precautionary guidelines. One option is to make the sewer piping to the same standard as the water pipe, in which case the piping may be installed closer together.

If you have PVC water mains, it is possible to have hydrocarbons migrate through the PVC.

 

[amlinerrichard]

Sewer mains should be below the water mains if possible.