Sewer gas

[Arcal]

The other day a plumber approached me with a question to which I had no answer. He was installing a sewer line to an existing house and when he cut into the line, pressurized sewer gas blew out of the line. (The house is at one of the highest points in the city and at the very end of the line.) He quickly made his connection and thought nothing more of the issue until he got a call from an irate customer the next morning. The house was full of sewer gas.

He went to the house and checked all of the traps, which were full, but noted that the gas was coming up through the water. He thought of putting a larger vent in the line, but decided that even though It may solve the problem in the house; it would not solve the problem outside, knowing the location of the house. He decided to put a 4" P-trap in the line outside of the house, hoping that would stop the flow of gas. This pretty much did the trick, except every morning when the trap in each sink is disturbed; they get a whiff of sewer gas.

He told me that the owner is adding a large addition to the house and that he is going to place a large vent pipe well above the roof at a remote location, hoping that it will be high enough so the wind will not bring it back into the yard.

Has anyone else dealt with this problem?

 

[Mac]

Re: Sewer gas

I'd look for some blockage of the house's vent system. Working as it should, gas ought to be able to circulate in - or out - the sewer lateral vent, into the house vents (and some drains) and go out of the exposed vent section that sticks out the roof, with no gas escaping into the house environment. Conversely, pressure shouldn't build up in the lateral without dissipating through the house vent system, and out the roof vent.

 

[Mule]

Re: Sewer gas

when he cut into the line, pressurized sewer gas blew out of the line.

This tells me that they may have some type of backflow device installed in their sewer line. With any type of pressure on the sewer line it would have been getting into the house. When the plunber replaced the line he got rid of the backflow decice and now the gases are getting in the house.

This tell me there is not proper venting. I don't think increasing the size of the vent will do any good if the existing vents are working properly. There plumbing board, at one time, talked about decreasing the size of vents required. Thet were even talking about going down to a 3/4" size vent.

Maybe the have studor vents installed every where! Had a backflow/backwash device intalled????

When I talk about backflow/backwash I'm talking about the device they install when a building sewer is flat or there are continuous problems with sewer backing back up into the house.

 

[JBI]

Re: Sewer gas

"...pressurized sewer gas blew out of the line."

Assuming this is a Municipal Sewer District, have you called the DPW guys yet? That doesn't sound right to me... There shouldn't be any appreciable pressure built up in the sewer lines.

 

[Uncle Bob]

Re: Sewer gas

Arcal,

"He went to the house and checked all of the traps, which were full, but noted that the gas was coming up through the water."

There is no reason for a properly vented system to allow pressure to build up in DWV system.

The plumber should go to each vent termination (on the roof) and run a cable through until he can see the cable in the building cleanout. Remove all traps and water closets and do the same thing. If there are (and there very well may be) air admittance valves installed; they may not be working and/or may be hidden in walls.

A stoppage in the vent system combined with a faulty "backwater valve" might cause this problem.

Regardless of the reason; SEWER GASES CAN AND DO KILL PEOPLE; sometimes within a few minutes. Absolutely, no work should be continued until this problem is solved; regardless of the cost or inconvenience.

You should contact the municipal sewer administrator and ask for their expertise. They are well aware of the dangers of sewer gases; and will be helpful in determining the cause and possible solutions.

Hope this helps,

Uncle Bob

 

[Heaven]

Re: Sewer gas

God what a way to go . . . . killed by sewer gases.

 

[Dr. J]

Re: Sewer gas

The suggestions regarding checking out the house's venting system are valid, but the possibility of a municipal sewer system problem should not be overlooked.

house is at one of the highest points in the city and at the very end of the line.

It sounds like this house's vent system is acting as the vent for municipal sewer system. As the high point, the natural stack effect of the system and the downhill flow of the sewer could be making the sewer gasses rise to the top as the water makes it's way downhill.

He decided to put a 4" P-trap in the line outside of the house, hoping that would stop the flow of gas. This pretty much did the trick, except every morning when the trap in each sink is disturbed; they get a whiff of sewer gas.

This is another clue that it is a pressurized sewer system attempting to relieve through the high point.

He was installing a sewer line to an existing house and when he cut into the line, pressurized sewer gas blew out of the line.

I assume this cut was made in the municipal line, not inside the house. Another clue it is the municipal system at fault.

It could be that the municipal system is undersized and running surcharged downstream of the house in question.

I have indeed seen this problem, where a large commercial facility was installed on the end (high point) of the municipal system in a new development. Lots of head scratching until it was determined that the municipal system was trying to vent through "our" vent system, since we were first on line.

The house may be part of the problem - if it was venting enough, the municipal system might not be pressurized, but the municipal system should not be relying on a 3" vent at the top of a hill in a private homeowners house in the first place.