Pacific Gas & Electric does not permit it.
Underground natural gas delivery is by plastic.
No way will PG&E suffer compounding fires -- electric then gaseous.
Common trenches out my way are restricted to power, data, coax... with various horizons at least 12" apart -- sometimes more.
Fresh water, dark water, fire systems, and gas are not permitted in the common trench.
Customer side power is not permitted in the same horizon ( depth ) as utility lines. Utility power is always to be the deepest in the trench -- except if crossing.