Do note that that facility doesn’t have 30 days of energy storage at max output. In a bad spell, as if the nukes go down, 27B gal reservoir, at 27MM gpm flow, gives you about 16 hours of water to empty. So multiply your 18M facilities by 45 to get your national 30 days of storage: 800M times that one facility!
The USA has enormous potential sites and water resources for pumped hydro.