I could not get in contact of Steam On Wheels--who we usually use for any type of pipe freezing problem. I've been told that they have been quite busy this past week. With temperatures dropping below zero for the next couple of weeks, I imagine that they will only get busier.
I know that part of the problem is that the leach field installed by the previous owners just before we bought the house was done poorly (the company that did it is no longer in business). However, we have not had this kind of problem before in the winter. This is usually an issue at break-up. We will need to do something about this in the future, but it is a massive expense.
For now, we need to find some way to melt or remove that ice blockage. I'm hoping to get in touch with Steam On Wheels tomorrow, and am not sure what to do if I don't.