Some interesting things I've found..

[jasonh1234]

Found a couple of things while playing with noclip.
The map is d1_trainstation_06
I sure don't remember seeing any of these things in the map while playing....

 

[LittleB]

That second one is where you go during the teleport mishap.

 

[AJ Rimmer]

That second one is where you go during the teleport mishap.

The first one might be the same. And the g-man is probably there so he can be spotted through the camera monitor in Kleiner's lab.

 

[xbulletholes]

The first one is the body of water you drop/ appear in just before you get attacked by the Icothysaur thingy, right?