Sergy, The dry stack IS NOT BUILT. I assume the youtube video your referring to is the one by Ficose. He just took a picture of where the dry stack will be. If it were built why go to the trouble of designing a new one?
They are proposing to use a site 6 miles from the mill for dry stacking. No milling has been done using dry stacking method at POW. The mill hasn't run since the cease and desist order (in 2005?)
And as far as the tailings (leftover dirt) returning to the mine it came from, I believe it will be in the case of open pit mines. But not right away. They will need a place to "park" the tailings for some time. That could be years. The tailings from a shaft type mine will not be returned. It just can't be done. Hope that answers a few questions!