Gas Line Depth


I'm going to be digging out a bush that runs right underneath the gas
line. According to JULIE, they don't say how deep the line is...just
that it's there. On my sidewalk right next to the outside turn-off
valve, it has ' 6" gas twp<?>" spray-painted on it. Before I start to
carefully dig, does this mean that the gas line is only 6" below the
surface? From what I recall, the line should run a foot or two
underneath the surface, which is deeper than I will dig. Also, for
what it's worth, I live in Chicago.

Just looking for some answers before I start my adventure...