Essex 19 Penstock Condition Assessment

Essex, Vermont

DuBois & King performed a FERC-level inspection and condition assessment report of the existing penstocks at the Green Mountain Power Essex 19 hydroelectric facility located on the Winooski River. The station was built in 1917, with the penstocks as part of the original facility construction. At the time of the inspection, there was minor leakage low in the penstock inverts.

The facility consists of an intake structure, four 9-ft-diameter buried steel penstocks, two 3-ft-diameter buried steel penstocks, four turbine generator units, a power house, and a tailrace structure. Longitudinal and circumferential penstock seams are constructed of lapped riveted joints.

Penstocks #1 and #4 were visually inspected from the intake to near the start of the spiral case, approximately 425 ft. Inspection consisted of visual observation, field measurements including shell thickness measurements taken at 50-ft stations. Areas of the shell were sounded with a hammer to estimate soil compactness to determine the presence of voids.

A condition assessment report prepared subsequent to the inspection documented the inspection activities, summarized field data collected, and presented stress analysis calculations. Recommendations included specific maintenance and detailed mapping through the use of ground penetrating radar.