The root zone ratio and the depth is great to work with. I don't know about scalping the old turf then adding 16" of the growing medium on top. Think of the thatch and the root system of the scalped turf, it would create a layer effect and could create a drainage problem, not good. You are far better off to sod cut the old turf out, then put down your root zone mix. If you don't want to put in subsurface drainage make sure you have at least 1% slope on the surface of the green. This will ensure no puddles on the green after a heavy rain, the excess water will flow off. If you go to my website you will see the green cavity, the pea stone layer, and the root zone mix going in, then the Poa cores, the total depth is 18".
I don't know where you got your information about building a USGA putting green, but you don't have to dig down 3' to create the green cavity? I have never seen or heard of pipes with water in them running underneath a putting green, too much potential for something to go wrong i.e. broken pipe washing away the green or if you had to do a repair, you would have to dig up a section of the green to get access to the pipes. Irragation pipes will run around the outside of a green, but never underneath.
Do you find it hard to maintain the health of your green keeping the stemp meter at 13 throughout the growing season, especially when the heat of the summer comes. I would be interested to hear about your Turfgrass cultural practices and if you use wetting agents. It sounds like you have a lot of fun with your green and that's important when you think of the time spent caring for it. Take care - Chopper.
