Text 
Dam work is done / Repairs completed a year ahead of schedule
By CHARLES F. TRENTELMANWILLARD BAY -- Repair work to the Arthur V. Watkins Dam around Willard Bay was declared finished this week, a year ahead of schedule.
That's good news for boaters who use Willard Bay. Since the dam sprang a leak two years ago, Willard Bay has had such low levels that the south marina has been closed half the time and boating everywhere was severely restricted.
Repair of the dam early is especially good news for the Weber Basin Conservancy District.
Willard Bay is the district's single biggest storage area. When the dam sprang a leak, the district had to let 100,000-acre-feet of water, an amount equal to Pineview Reservoir, flow into the Great Salt Lake.
Since then, the ability of the bay to store water has been cut in half.
Repair of the leak involved fixing the whole dam so it wouldn't leak again.
Brandt DeMars, field engineer for the Bureau of Reclamation, said investigators found that a nearly 5-mile section of the dam was built over sandy lake bottom left over from historic Lake Bonneville.
The leak that sprang two years ago was due to that sandy soil, he said. Water seeping through the sand slowly "piped," digging its own channel, and finally came bubbling up on the outside of the dam's southeast corner.
A year of testing found that the dam's structure was sound, but the ground under its entire south and southeast sections was all like beach sand, susceptible to more leakage and piping.
The solution was to dig a ditch down through the dam, through the sand and into the clay underneath, then fill that ditch with a cement-bentonite wall. The result is a sort of dam within a dam, an impervious wall in the sandy subsoil locked to the clay.
Starting in August, the Bureau of Reclamation contractors started digging the massive trench, 30 inches wide and an average 56 feet deep, using a claw that could reach as much as 70 feet.
While that claw was digging, other workers were pumping the cement-bentonite slurry into the trench.
Bentonite is a type of clay usually used in oil drilling. Mixing it with cement makes it set up but not real hard, kind of like cement jelly, impervious to water but still flexible so it won't spring leaks.
As the claw dug, the slurry was pumped. A plant to make the slurry on site moved with the digging.
DeMars said the project dug a trench about five miles long. Originally the work was anticipated to be half done this year and completed next year.
Why was it done early? To cut their own labor and equipment costs, the contractors -- Nordic Industries of Marysville, Calif., and Geo-Solutions of New Kensington Pa. -- worked real hard. They put on double shifts and worked around the clock, seven days a week.
As a result, instead of having the cement-bentonite wall built by November of 2009, they have it done now.
The final numbers are impressive: In 166 work shifts they averaged 170 feet per shift, used 26,000 tons of cement and poured 179,338 cubic yards of slurry. The finished slurry wall is 28,000 feet long, just over five miles, in the 14.5 mile-long dam.
Some finish work remains that will be completed next spring. That includes smoothing and grading the sides of the dam and building a road along its top. But, he said, the critical part, the cement-bentonite wall, is done.
Completing the job early doesn't save the Bureau of Reclamation a lot of money because the contract calls for the contractors to be paid by the cubic yard of wall built, he said. The wall itself cost $14,127,669. The whole contract, including finish work, is $18 million.
However, he said, finishing the work a year early has enormous benefits.
Assuming spring runoff allows, the Weber Basin Water Conservancy District can refill Willard Bay all the way to the top next year. Boaters won't have to worry about going aground any more.
And the Bureau of Reclamation won't have to spend money sending DeMars out to Willard Bay every day to monitor the project.
Add Your Comment
I learned my boating skills here. This where my children learned to water ski.
It will be nice to get back to where we all started. Well done to the crews who saved my lake.
Please read our posting guidelines before reporting a comment.