Geo-Solutions, of New Kensington, Pa., is to dewater surface and subsurface levels of the dam's embankment foundation, excavate and place new embankment fill material, build a five-mile-long cement-bentonite cutoff wall to intercept seepage, and install new foundation drains.
BuRec announced the contract award May 28. On-site work is expected to begin in June and be completed by November 2009.
Watkins Dam nearly failed in November 2006 as the result of piping and internal erosion of foundation soils. BuRec and the Weber Basin Water Conservancy District determined a portion of the dam's foundation had eroded, leaving a small number of two- to five-foot-wide sinkholes near the toe of the dam.
In response, BuRec and the district drew down the reservoir to a safe level and applied sand, gravel, and other materials to key locations. BuRec performed geologic investigations through most of 2007. In January 2008, a study proposed the new five-mile cutoff wall through a portion of the dam's profile.
Watkins Dam is 12 miles north of Ogden. Portions of the embankment were built in 1955, 1964, and 1989. The 10,000-acre Willard Bay off-channel reservoir behind the U-shaped dam was designed for a capacity of 215,000 acre-feet, and usable storage area of 198,200 acre-feet.
BuRec transferred responsibility for operating and maintaining the dam, part of the Weber Basin project, to the water conservancy district in 1969. The Weber Basin project provides water for irrigation and for municipal and industrial uses to areas east of the Great Salt Lake.