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Reservoir repairs may include expansion

CLEARWATER — While Tampa Bay Water's gigantic reservoir is being repaired, it could also be expanded.

The reservoir in rural Hillsborough County is already the largest in the state, holding up to 15 billion gallons of water. But the walls have been plagued with shallow cracks, so now the wholesale utility is lining up contractors to repair it.

The repair work will require draining the reservoir for two years, senior engineering manager Jon Kennedy told the utility's board Monday, so why not use this time to make it 3 billion gallons bigger?

"It's going to be out of service anyway," Kennedy said.

The reservoir is now full, he pointed out, but "we could've put additional water in the facility if we'd had the room."

So the staff is asking the firms bidding on the repair job to include an option to expand the reservoir to 18 billion gallons, he said.

But there are limits on how the expansion would work. For instance, they could not expand the reservoir's current footprint, Kennedy explained. Doing that would require getting new state and federal permits that could make the work drag on a lot longer than two years.

Instead, the contractors must figure out how to build the sides of the reservoir higher so it holds more water, he said, a process called a "dam raise." And they have to be able to do it within the same two-year period already planned for the repair work, he said.

At this point, Kennedy said, the staff cannot predict how much expanding the reservoir might cost. The current repair estimate is $125 million, nearly as much as the $146 million the facility cost to build.

"That's why we're asking the market to price it," he explained. If the expansion costs too much, or causes too many complications with the repair, then the board can turn it down.

The utility opened the C.W. Bill Young Regional Reservoir in June 2005 as a place to store water skimmed from the Alafia River, Hillsborough River and Tampa Bypass Canal. The reservoir, named for the longtime congressman from Pinellas County, covers about 1,100 acres.

The reservoir's walls consist of an earthen embankment as wide as a football field at its base, averaging about 50 feet high. An impermeable membrane buried in the embankment prevents leaks.

The embankment's top layer is a mixture of soil and concrete to prevent erosion. That's what cracked in December 2006. Some cracks were up to 400 feet long and up to 15½ inches deep. Workers patched the cracks, but the fix didn't last.

An investigation found water is getting trapped between the soil-concrete lining and the membrane. As long as the reservoir is full, the trapped water remains stable. When the utility draws down the reservoir, though, pressure increases on trapped water in some areas, producing cracks and soil erosion.

The utility's board would vote on whether to approve the expansion when it approves the repair contract. Kennedy said the staff will send out a formal request for proposals next month, with a deadline of March for submissions. Then the board will vote on them in June.

The board, with no discussion, voted unanimously to approve a list that Kennedy presented them of four design-build firms to do the repairs. They are Granite Construction Co.; Kiewit Infrastructure South; MWH Constructors; and Skanska USA Civil Southeast.

Unlike the company that built the earthen-walled reservoir, all four potential bidders have experience with this type of construction.

The board had sued the three companies involved in the original reservoir construction. On Monday, it approved a settlement of $6 million with CDG, the company that provided construction management. The suits against HDR Engineering and Barnard Construction are continuing, general manager Gerald Seeber said.

Craig Pittman can be reached at craig@sptimes.com.

Reservoir repairs may include expansion 10/18/10 [Last modified: Tuesday, October 19, 2010 8:13am]
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