Northfield Mountain Pumped Storage Project: Performance

The Northfield Mountain Pumped Storage project consists of a lower reservoir formed by Turners Falls Dam on the Connecticut River, an underground powerhouse and surge complex. A rock-fill, concrete-faced dam was also considered, and bids indicate that costs were comparable to the earth core section. A multiple row grout curtain was effective in preventing significant leakage from the upper reservoir. Seepage into the powerhouse has been minimal. Settlement of the upper reservoir dam has been somewhat greater than anticipated, probably due to the rapid cycling of water level, and is expected to reach about 1.1% of the height of the dam after 50 yr. Extensometers installed in the powerhouse showed initial elastic response during construction, but have shown no movement over a subsequent 8-yr period. Elastic response of the powerhouse walls to hydraulic loads was measured with sensitive diamagnetic tiltmeters.