We have run across a 500 gallon above ground LPG tank that was installed in a detention pond/drainage easement. Our storm water inspectors noticed this and posed the question to me. I've not been able to find anything explicitly in NFPA 58 that prohibits this, outside the tank being partially submerged several times a year. I've attached a picture if it helps.
An interesting point is that North Texas had some pretty epic rainfall earlier this year and most, if not all, of our detention ponds were full for an extended period.
Any help would be appreciated. Thanks.