The drill stem is all the way at the bottom of the well, and is being used to pump compressed air down to the bottom of the well, which obviously forces the water up to the top. Then, according to Boyd, they just let it run like this for hours and hours, which helps get the fine sands and other materials cleared out ensuring a nice clean, non-sandy water supply.
Finally, for fun I used some of my l33t Paintbrush skilz to create a cross-section of the well:
The screens are held tight against the bottom of the hole (by the drill stem - not shown in above drawing - extending down inside the screens to the very bottom), while the casing is moved up and down to expose more or less of the screens to the aquifer. This is what I mentioned in my last post, but the above drawing makes it more clear, I think, how things really look. :)