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Consultant May Know Reason For Reservoir's Issues

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By STEVE ANDREWS | News Channel 8

Published: August 27, 2008

A state consultant thinks he may have an answer about why Tampa Bay Water's regional reservoir wasn't built according to plan, but he says he isn't sure how it was missed.

Heavy machinery may be to blame for a thinner layer of soil cement than what plans for the reservoir in southeast Hillsborough County required, he says. Soil cement lines the interior walls of the reservoir and helps control erosion.

David Carrier, a geo-technical engineer, was hired by the Florida Department of Environmental Protection to monitor the safety and stability of the $146 million reservoir.

Engineers have not figured out why cracks continue to weaken the soil-cement walls in two corners of the 930-acre C.W. Bill Young Regional Reservoir, which stores excess water from rainfall.

Tampa Bay Water diverts water from rivers to the reservoir when flows are high, a tactic intended to limit the need to draw water from diminishing underground supplies.

The reservoir's interior walls slope until they reach an area called the bench. The bench is the spot where the slope levels off. Construction plans called for 12 inches of soil cement on the bench. However, divers inspecting the bench area last November discovered only 3 inches of soil cement in some locations.

Carrier's theory is that heavy equipment spreading the soil cement along the bench might have been the cause.

"We're talking about the corner of the bench and I think the equipment operated along there. They squeezed out the material and it was probably deposited somewhere else," said Carrier. "Somewhere else there's a section that's thicker than originally planned."

Tampa Bay Water acknowledges that the reservoir was built with less soil cement than plans called for, although they haven't offered an explanation.

Despite density tests and drilling by engineers and consultants to determine the thickness of the soil cement during construction, no one realized the soil cement in areas of the bench did not meet construction specifications.

"This is speculation, I believe that 12 inches was placed on the spot but in the process of working the material it ended up being thinner," said Carrier. "I don't have an explanation for you as to why this specific area was not caught,"

For more than a year experts at Tampa Bay Water, as well as design engineers, have struggled to control cracking in the soil cement. Repairs, which consist of pouring grout into the cracks, are cracking as well.

Tampa Bay Water expects to spend at least $1 million filling the cracks and keeping them filled.

"The dam is safe," said Carrier. "We're working hard on it to keep it safe."

Identifying the cause of the cracks is the first of four steps needed to repair the reservoir, says John Kennedy, a staff member of Tampa Bay Water. After identifying the cause, Tampa Bay Water will propose a remedy for the cracks, as well as a way to prevent cracks from forming.

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