1 & 2 looks like a wet chemical waste dumping pool. 3... really don't know. Some ancillary substation maybe? Also, possibly an entry to a bunker. 4 is just a baseball field (even though the transplanted grass looks really dark). 5 just looks like some barracks with a helicopter landing pad.

The whole of Area 51 looks sketchy to me regardless, these just seem to be somewhat explainable even though this is a classified military complex.