On Tue, 08 Apr 2014 09:24:50 -0400, "Percival P. Cassidy"
wrote:

Anyway, we were not offered the option of using polyethylene: PEX or
copper were the choices, and we're going with PEX.

You could just abandon the present pipe, and trench for the new PEX.
Avoid close-by trees (roots). Bob mentioned using PVC to shield the
PEX. That is a good idea, but at an extra cost.

PEX gas lines I've seen buried were backfilled with sand and
compacted. The street was trenched to bring gas to the other side of
the street, for a new house being built.