Mike, the 2001 California Plumbing Code states the minimum cover for horizontal metallic gas pipe to be 12". Also, 1211.7 "Underground ferrous piping shall be electrically isolated from the rest of the gas system with listed or approved isolation fittings installed a minimum of six(6)inches(152mm) above grade.
I don't know the horizontal distance required by code, but PG&E wants a 6" minimum (12" typical) horizontal separation.
The electrical pipe cover depends on the pipe material(or direct burial cable), voltage, vehicle traffic and if concrete will be used as cover.
