Grandpa Dan wrote:
Cubby,
I don't know where you are living but frost doesn't go any lower than approx
20 inches in the ground. In cases where there is no snow, frost may go as
much as 36''.

I'm not going to comment about the sewer problem
except it is most likely a plugged field. The OP
should have done something about it the first
time. It is unlikely to be frozen, but to address
your comments on freezing depths.

Your information on freezing depths is not
correct. Although fairly unusual, frost depths
can go to 6 feet and did so in 1990 near here.
Frost depths of 4-5 feet are fairly common at
elevations of 5000 or more.

In 1990 the frost line in a town about 50 miles
away went to 6 feet and caused a lot of headaches.
Four feet deep is not uncommon for a frost
depth. The county extension office or a city
building permit agency will information on the
frost depth is in your area. People that live in
the lowlands tend to think everyone experiences
the same conditions.