First off, those miners are NOT located at hydro dam site. That's a rented warehouse.

Andreas stated that it's a secret location, but HydroMiner is on record in stating that they offer regular tours of their facilities to H20 token holders, among others.

HM just purchased ~800 S9 bitcoin miners but ONLY 240 are shown in this facility. Where are the rest?

Andreas alludes to reading this thread.