The Northfield Mountain Pumped Storage Project took four years to build, and when it opened in 1972, it was one of the largest pumped storage facilities in the world. Today it is one of the ten largest pumped storage plants in the USA. Water is pumped in and out of the Connecticut River at an unmarked intake/outfall connected to a 320 acre reservoir atop Northfield Mountain, 800 feet above the river. Filling the reservoir takes 11 hours, and draining it takes eight hours. The four turbine/pumps in the powerhouse generate as much as 1,168 megawatts of power on the way down, but consume around 30% more than that on the way up. The powerhouse is deep inside the mountain, and all the pipes and penstocks are underground too, bored through solid granite. Like many other pumped storage plants of this era, Northfield Mountain was constructed to balance the power grid for a nearby nuclear power plant, in this case Vermont Yankee, a few miles up the Connecticut River, just over the state line, in Vermont.
