Vapor Barrier / Retarder Below WWTP Tanks 2

[jjezmarlo3]

I have been researching the need for a vapor barrier / retarder below slabs-on-grade for environmental tanks (WWTP, WTP, etc.) I have found example drawings from firms that show the use of a vapor barrier below the tanks, while I have found example drawings from other firms that omit the barrier. I'm not sure what the need for a vapor barrier below WWTP tanks would be, and it is a costly item that may induce curling in the slab. Has anyone run across this item before?

 

[JAE]

Not sure why you'd need a vapor barrier for WWTP tanks. Doesn't make sense to me.

 

[Hemifun]

The company I work for does a lot of WWTP work involving the design and construction of concrete tanks and we never put vapor barriers below the tank slabs. It has never resulted in a problem of which I am aware.

 

[jjezmarlo3]

Thank you both for your input. I believe not using a vapor barrier is the correct way to go. You just start to second-guess yourself when you see examples of others doing things differently.