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Plbg.com also known as the PlumbingForum.com. The popular plumbing tips, remodel and advice forum and blog. Ask any toilet, sink, faucet, pump, water quality and plumbing related questions.
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Author:
SwimRunPlumb (MI)
I have to quote a job where I need to reroute a sewer line outside.
The back of the house was an addition on a slab and leads to the septic. The front of the house has 1 stack and has been re-routed to go out the front to the city sewer.
I have to cut it and re-route it (about 60') outside in the back of the house to come back into the basement and tie it into the stack so that the whole house is on the city sewer.
My question is how deep do I need to be? The frost line in Michigan is 36" I believe. The line to the septic tank is very shallow, but also very short. Do I need to be 3' down, or is it a non issue since it will be flowing and carrying warm water?
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Author:
johnjh2o (FL)
The warm sewer gas should prevent the line from freezing.
John
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Author:
packy
2 possible problems. one being a slow dripping faucet or running toilet. that small amount of constantly slow running water will freeze. the other potential problem is a partial stoppage. the puddle of water behind the stoppage will freeze.
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Author:
jimmy-o (CA)
I think you will find most of Michigan to be 42" frost line, with parts of of northern MI deeper
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Author:
joe plumber (NE)
About the only thing "warm sewer gas" might do is cause hoar frost .
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Author:
bernabeu (SC)
!
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Measure twice, cut once.
Retired Plumbers Local Union #1
Edited 1 times.
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Author:
johnjh2o (FL)
Please explain to me why the line to septic tanks don't freeze. They are never any more the 2' underground in areas were the frost line is 42".
John
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Author:
North Carolina Plumber (NC)
Here in the NC mountains, water must be at least 24" deep. Sewer pipe has to have at least 2" of cover.
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Author:
johnjh2o (FL)
What do you do with your septic systems? They cant' be that deep.
John
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Author:
bernabeu (SC)
!
- - - - - - -
Measure twice, cut once.
Retired Plumbers Local Union #1
Edited 1 times.
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Author:
johnjh2o (FL)
DOH Leaching fields are not below the frost line.
John
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Author:
bernabeu (SC)
as per: [www.engineeringtoolbox.com]
Quote:The leach line dimensions depends on the required capacity of the system. As a guideline
•the maximum length of each line should not exceed 100 ft (30 m)
•the spacing between lines should not be less than 10 ft (3 m)
•the minimum depth of the leach line should not be less than 12 in (0.3 m) or deeper if the soil freezes during wintertime
•the elevation rate should be approximately 1%
imo: while the pipe itself may be 'in the frost-line zone' ..... the gravel bed must extend below while remaining ABOVE the ground water table ..... the complexity of designing a PROPER WORKING system renders it virtually impractical except where there is no other choice ..... hence the REQUIREMENT to connect to a public sewer where/when/if it is available
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Measure twice, cut once.
Retired Plumbers Local Union #1
Edited 2 times.
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Author:
johnjh2o (FL)
I lived in the North East were the frost line is 42" and have have never seen a septic system installed below the frost line. And that is in a fifty + year period.
Here are two Rules of Thumb for Drainfield Depth that should probably be universal:
1. Vertical Separation bottom of drainfield rock or plastic vaults to water table or restrictive rock layer etc = 2 foot minimum.
2. Maximum drainfield depth from finish grade to bottom of drainfield vaults or gravel = 3 foot maximum.
John
Edited 1 times.
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Author:
Scotwperry (MI)
Michigan plumbing code requires that municipal sewers be 42 inches deep or more, however sewers feeding into a septic tank need only be 12 inches deep, and so in Michigan these are the depths that municipal sewers and septic system sewers are commonly layed. The reason that septic system sewers can be more shallow is because the septic tank is constantly generating a certain amount of heat. This warmer sewer gas will reverse back through the septic sewer and up out through the house's sanitary vent stack. Municipal sewer systems do not have the benefit of the heat that comes from a septic tank, thus they have to be buried deeper.
Scott: Master Plumber
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