Gringey City was featured in the episode Sparks Fly For Magnemite. Ash's Pikachu was sick, and the nearest Pokémon Center was located there. Suddenly, the power in the town went out. This was due to a large amount of Grimer clogging the tunnels where the water went to power the generators.
It's likely that Gringey City is based on Kanto's Power Plant in the games, since Muk was added to the Power Plant in Pokémon Yellow.