Tampa Bay Water to fix reservoir at estimated cost of $125 million

06/15/09 Seán Kinane
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This morning the board of Tampa Bay Water directed its general manger to implement a long-term fix for the region’s damaged reservoir. It is expected to cost about $125 million.

Cracks that formed more than two years ago in the state’s largest reservoir have been temporarily patched. The 15.5-billion-gallon-capacity reservoir -- which was essentially empty in the beginning of May – is being filled and now contains about 2.1 billion gallons. But the first step in a five-year process to implement a long-term fix was taken on Monday, according to Jonathan Kennedy, chief engineer with Tampa Bay Water.

“Today the board took decisive action to put us on a path that’s going to implement a long-term fix for this project. … It’ll be a combination or rely on any of three approaches. One would be a buttress to weigh it down so that its drainage characteristics are not relevant. Second would be to add a drain feature to the existing soil wedge. And a third would be to remove it entirely and replace it with a more porous layer.”

Tampa Bay Water hired the consulting firm Black & Veatch to determine the cause of the cracks in the soil-cement layer lining the interior of the C. W. Bill Young Regional Reservoir in southeast Hillsborough County. They used instruments called piezometers to collect data on pore pressure in a soil wedge below the soil-cement layer. Helen Bennett is with Black & Veatch.

“What we learned from the piezometer data is that the soil wedge is not draining at the same rate as the reservoir stage. And that excess net pressures are increasing as the reservoir stage declines. … Here with the reservoir full, the soil wedge is saturated. And the water level in the soil wedge is approximately the same as the water level within the reservoir. As the reservoir draws down, water is trapped behind the soil-cement. The pressure difference behind the soil-cement increases as the water level drops. The water trapped behind the soil-cement causes pressure on the soil-cement and that’s what leads to the cracking.”

Bennett says that 40% of the reservoir is already affected by cracks, but that the whole perimeter will eventually be affected. For that reason, the fix will be applied to the entire reservoir. Chief engineer Jonathan Kennedy says the repairs can only occur when the reservoir is dry, which means it will be out of service during construction.

“With normal to above-normal water conditions as far as rainfall goes, we should be fine to be in compliance with our groundwater permits. However, if we’re below-normal rainfall, and especially if we are below-normal rainfall for the two years that we would be out of service, we would have to take a very hard look at the demand-management activities to make sure that we’re making our best efforts to stay in compliance. But at this point we’re showing you that we would anticipate, we would have a two-year cycle, two years – two drawdown cycles and two fill cycles -- where we would be out of service.”

Water customers won’t have to pay higher rates for the construction until financing for those projects begins in one or two years, according to Koni Cassini, Tampa Bay Water’s finance director. She says that if the long-term fix ends up with a price tag of about $125 million, the region’s wholesale water distributor will charge its member governments in Hillsborough, Pasco, and Pinellas Counties an extra 13 cents per thousand gallons. But those rate increases would be offset by any costs recovered by Tampa Bay Water in litigation against the companies that designed, built, and oversaw the construction of the flawed reservoir.

“Approximately $10 million in capital costs turns into a penny. So depending on what the cost is going to be, it’s approximately 13, 14 cents on the rates. And at this moment, we’ve adjusted what we think we need for facilities into the future, which means that the facilities that you’ll have and that you’re currently building will last a little bit longer. But it will have approximately a 13 cent impact increasing the rate.”

Tampa Bay Water board member Scott McPherson, who is Mayor of New Port Richey, has “a very big concern” about making sure that future construction does not contain flaws like the original design.

“Really, what it boils down to is there is a very serious problem in the engineering. And we’ve heard about the soil wedge, we’ve heard about the permeability. I’m not an engineer, and I'm trying to understand with a project of this size that cost the public this much money, how there was such a flaw in engineering. … How do we insure in the future, not just with this project, but that proper engineering is done? This board has to rely on the engineering of our projects.”

Jonathan Kennedy, chief engineer with Tampa Bay Water, responds that a peer review process will be used to make sure the design and construction of the long-term reservoir fix is appropriate.

“We want to bring the experience of other facility owners and constructors to the Tampa Bay community to make sure that we’re getting the best value in the long-term fix.”

The next Tampa Bay Water board meeting will be August 17th.

Tampa Bay Water

previous WMNF coverage of reservoir

Reservoir soil-cement cracking fact sheet

Reservoir inspection report

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