Wet Pit and condenser cooling water.
Here is a scan of a cross section drawing of the boiler house, showing the wet pits and details of the floor levels; main floor level 16′ OD, sub-basement (pump pit level) 0′ OD, wet pit floor -5′ OD.
A sketch of the original cooling water intake / discharge arrangement as I remember it from seeing drawings (over 30 years ago so I don’t guarantee accuracy), the valves to swap the intake / discharge according to the tide were operated from the platform over the cooling water pit.
