Hi all. I'm looking at lots of land to build on and one lot has my interest peaked. It has already been approved for a septic tank - Drip Irrigation septic tank, approved for 4 bathrooms. I called up a local company that installs and asked about it and she said it's a 'last resort' type of tank that is picked when the soil isn't deep enough to put in a different type. She speculated they got 3-5 feet down and hit rock or clay.

I'm not really sure what to think about that. Do any of you have experience with this type of situation or tank?

The lot is in the greater Seattle area, and is next to Tiger mountain. The lot is flat but because it's next to tiger mountain I am assuming they hit rock.