According to :

I wouldn't take w_tom's comments about burial depth _too_ seriously,
other than considerations for frost depth. Especially since you
have a cold water line here, you need to check that 18" is
_below_ your frost line. It might be. But it certainly ain't
here (it's more like 60" here).

18" might be enough for Maryland, but I don't know.


3) The water and steam pipes are all adjacent, while that gas lines
average about 1 foot above them, and are separate from the water and
each other. Should hot and cold water be insulated together?

I don't know what the gas line burial requirements, but 6" seems
awful shallow.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.