Northfield Mountain (hydroelectricity facility)
Northfield Mountain is a pumped-storage hydroelectric plant and reservoir located on and under the similarly named Northfield Mountain in Erving and Northfield, Massachusetts. It is currently owned by FirstLight Power Resources (formerly NE Energy), which purchased the facility from Northeast Utilities in 2006. History. Engineering studies for the plant began in October 1964, with early site preparation starting three years later. In 1972 its hydroelectric plant became operational as the largest such facility in the world. The facility was built to balance the supply from the nearby Vermont Yankee Nuclear Power Plant. Design. The plant  was built entirely underground, and located about up the Connecticut River from Turners Falls Dam. A stretch of the Connecticut River, extending some north from this dam to the Vernon Dam, Vermont, serves as the station's lower reservoir. During periods of lower electrical power demand, the plant pumps water from this lower reservoir through the Northfield Mountain Tailrace Tunnel to a man-made upper reservoir. At times of high demand, water is released to flow downhill from this upper reservoir through a turbine generator, where it then collects in the lower reservoir to be stored until again pumped to  the upper reservoir. Northfield Mountain's upper reservoir covers at above the river, with total storage of of water. Its underground powerhouse lies at below the surface and is accessible through a -long tunnel; it includes four large reversible turbines, each of which can pump of water per second and release of water per second to generate of electricity. The turbines can ramp up in 10 minutes, and deliver full power for 8 hours.