Thanks Steve. I really don't think the septic is undersized. We've got
two of us living here both of which are pretty frugal with our water use.
But I will try to determine what size is in there and go from there. The
contractor that built the house is pretty reputable and we haven't added
water using devices besides what were already installed by them. Any ideas
on how to troubleshoot a septic without digging up the entire yard?


The two possibilities a
(A) You're putting too much water into the system, or
(B) The system isn't getting rid of the water fast enough.

Is there anything besides your household waste-water that's
plumbed to the septic system? Storm-drains? Pool overflow?

You can inspect parts of the drainfield by running a
camera down it to look for blockages. You'll probably
have to dig a pit on top of the distribution
box if it's a multi-branch system.

You can see if the drainfield is working properly
by sticking a boot on the outflow-pipe and running
a garden-hose into it while watching the water-meter
(if any) to see how many gallons/minute the drainfield
will absorb.