Originally Posted by jgiacobbe
the sewer line is blocked by tree roots. .
Dr. WhipIt is correct. I had the same problem and having it professionally cleaned/augured out actually relieved the problem for a quite a while. Mine didn't back up again for a year after having it cleaned. It was only when it backed up a second time that I called a 'real' plumber who scoped it and determined it was roots. If you get it cleaned out it should work fine until you figure out how you want to proceed.
Definitely call the county and have it looked at also. Henrico county was very helpful when I had a problem and sent crews out to flush the lines and replace the connection to the mainline. Unfortunately the county was only responsible for the short distance from the meter to the curb.