Sand capping has always been a bit of a mystery to me.
1) 6 inches doesn't seem like very much, even though I recognize it would be a massive and expensive task just to do that over several dozen acres of undulating terrain. What kinds of checks are in place to ensure an even distribution to avoid getting 9-10 inches in some places and only 3-4 in others?
2) For sites that have readily available sand and areas in need of capping, is it common to increase that depth to say 2-3 feet?
Kalen:
The materials cost for sand capping is very high, so contractors [and owners] do their best to keep the cap depth as low as they are assured it will work. Frequently we have the agronomist recommend 12 inches to begin with, and by the time we get to construction, it's decided that 8 or 9 inches should be enough, because that will cost 25% - 33% less.
The only place I know that ever capped to a depth of three feet were the handful of holes along the cliffs at Pacific Dunes. Dave Wilber recommended we cap them extra deep if we wanted them to drain like the rest of the holes, so we just mined out a dune ridge from further inland, and used that material. We estimated the in-house cost at a little less than $1 per cubic yard for that material . . . when you are bringing it in from outside it can be $20 per cubic yard or more.
You need somewhere between 50,000 and 80,000 cubic yards to cap the fairways a foot deep, based on 30-50 acres of capping. Do the math, and you can see why everyone wants to skimp on the depth of capping. But if you skimp too much, the water won't release out of the profile very well, and you'll be playing second shots off the equivalent of a damp sponge.