Bury it deep enough, and it *will* *not* freeze. It really *is* that simple.

I grew up in Minnesota, and even there the code only calls for 42 inches.

But it _does_ need to be below the frost line.

The code may call for 42" at 8000 degree days and 48" at 10,000 degree
days but certain combinations of weather, snowfall, and ground use can
easily drive the frost in a full 6'. A lightly used, shaded parking lot
on the north side of a building with a string of below average temp days
will do it. Even then, it is usually only a problem if you have no water
usage.

The road construction crews will commonly bury insulation between storm
sewer manholes (no flow in the winter to warm things up) and the
adjacent water lines and sanitary sewer lines.