A few weeks ago, we had a backup that resulted in septic waste in our basement. We had the tank pumped, and the regulatory agency performed a dye test. There is no dye showing up in the leach field or down hill from it (good). This was after a period where we had over 9 inches of rain in two weeks (thanks to Irene and Lee). In the intervening 10-days, we have had almost another 3 inches, and today I realized that the tank had filled AND overflowed a little (the tank is still uncovered as I wanted to see what happened before I filled in the hole).
The septic system is, we guess, > 10 years old (maybe as old as 23 years, and we have never had any trouble with 2 pump outs since 2001.
What do people think about the probability that the leach field is just not draining fast enough because of all of the rain? Nearby there is surface water running (where it usually does not run) at about the same elevation as the leach field. It would not surprise me if the leach field is saturated with groundwater. because of all of the rain.