It would be pretty economical to own a generator and the tanks as required, not have a generator at each site

Also seems like it’s only during construction and repair. They’re not constantly pressurized. (Or rather, Nitrogen is used to sypplement)

Not entirely clear but I think they mean they flush the sewers with the nitrogen, not actually pressurize them with the nitrogen?

The cables have a protective sheath covering them, but during construction and repairs, the steam build up in some of the sewers can be too much for them — so they use liquid nitrogen expanding into gas to supplement the pressurized cables in order to keep the them dry.

Think a nitrogen generator is a few thousand?