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Reservoir Safety On Thin Cement

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By MIKE SALINERO

The Tampa Tribune

Published: July 1, 2008

Updated: 07/01/2008 11:45 pm

TAMPA - Divers checking cracks in the C.W. Bill Young Regional Reservoir have discovered the cement holding billions of gallons of water is more than half a foot thinner in some places than it's supposed to be.

Engineering specifications for areas near the base of the reservoir walls call for the cement to be 12 inches thick. Divers discovered in November that the cement was as thin as 3 inches in some areas.

Despite the cracks and thickness problem, Tampa Bay Water officials insisted Tuesday there is no cause for concern.

"Saying it is too thin suggests there is a problem," said Donald Polmann, director of science and engineering for Tampa Bay Water, the regional water supplier. "We have no evidence the soil cement's thickness correlates with any failure of any type. The thickness is an issue we've been studying. We have not concluded that there is a problem per se."

Polmann's assurance did not comfort residents who live near the 930-acre reservoir in eastern Hillsborough County. For more than a year, they have listened as Tampa Bay Water engineers described gaping cracks in the reservoir's inner wall as a "maintenance problem."

"They're going to claim that until the day we're dead," said Janda Fussell, whose family lives on 40 acres adjacent to the reservoir walls. "I don't trust Tampa Bay Water when they say it's structurally fine, but then there are these cracks and gaping holes."

Divers discovered the thickness problem in November in an area engineers call the "bench," where the sloping walls level out. That information was never shared with the utility's board members or residents who live in the shadow of the reservoir's 50-foot-high berms.

"I can only tell you I wasn't apprised of that," board member and Councilman Charlie Miranda said.

The findings by the divers came to light this week after a reporter for News Channel 8 started asking questions. Tampa Bay Water then sent an e-mail to board members Tuesday informing them of the depth of the covering, which is made of a mixture of dirt and cement.

"We are continuing to investigate the thickness of the soil cement as part of the cracking investigation," the e-mail said. "Once we have more data, we will decide on a recommended course of action to the board."

The contractor that built the reservoir, Barnard Construction Co. of Bozeman, Mont., did not return a telephone message. A three-year warranty that would have required the company to fix the thickness issue expired Feb. 2.

Bozeman was chosen to build the reservoir with a low bid of $86 million. The soil cement covering the inner walls was made by mixing 8 to 9 percent cement with soils excavated during construction. Because the soil cement does not contain gravel, its strength under compression is about one-tenth that of typical concrete.

Tampa Bay Water chose the soil-cement mixture to stabilize the banks because it was less expensive than chunked rock called riprap.

Tampa Bay Water officials have long maintained that the soil cement is doing its job of erosion control and breaking the energy of waves. They said they expected cracking in the covering, although not to this degree.

"If you look across the entire interior, you will see cracks everywhere," Polmann said. "That is expected. What is at issue is about 5 percent of the area where the cracks are larger than expected, and those are being filled."

No leakage has been detected in the reservoir's walls, Polmann said. The soil cement sits on top of a fabric that controls erosion. Below that is a plastic membrane that controls seepage. All are intact, he said.

Engineers with HDR of Omaha, Neb., continue to investigate the cause of the cracks, which number between 200 and 300. One theory is that the soil cement was stressed as reservoir levels fell during the drought. Engineers say it's also possible lowered water levels changed the pressure dynamic on the walls by eliminating the outward pressure.

Tampa Bay Water has spent about $700,000 since early 2007 filling the cracks. The water supplier has budgeted another $500,000 for the cracks in the fiscal 2009 budget. All the cracks should be filled by next week, Tampa Bay Water spokeswoman Michelle Biddle Rapp said.

Board member Al Higginbotham, a Hillsborough County commissioner, said he believes Tampa Bay Water executive director Gerald Seeber when he says the reservoir is safe. But Higginbotham wants Seeber to find out who is responsible for allowing substandard work on the bench wall.

"An inspector had to sign off when that construction was going on," Higginbotham said. "Someplace in the construction documents you have an inspection."

Construction on the reservoir was finished in 2005. It was built to store rain and water from rivers during high flows so it could be used during the dry season. At capacity, the reservoir can hold 15 billion gallons, but now holds just less than 4 billion gallons because of a long dry spell.

Tampa Bay Water, which is in charge of the reservoir, supplies water to Hillsborough, Pinellas and Pasco counties, and to Tampa, St. Petersburg and New Port Richey.

The utility is considering building another reservoir in the same area. That worries some nearby residents.

"Since they're already talking about building a similar one besides it, that's double the trouble, double the worry," said Gayle Pollock, whose back door is 700 feet from the reservoir. "If they didn't build the first one right, what makes them think they can build the second one right?"

Reporter Mike Salinero can be reached at msalinero@tampatrib.com or (813) 259-8303.

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