The board of Tampa Bay Water has approved an estimated $125-million repair program for the agency’s four-year-old, 15.5-billion-gallon C.W. “Bill” Young Regional Reservoir. The facility, which cost roughly $140 million to construct originally, has been experiencing significant cracking since late 2006. The authority is also moving ahead with a lawsuit against the three lead members of the original project team: HDR of Omaha, Neb., the designer; Barnard Construction of Bozeman, Mont., the contractor; and construction manager Construction Dynamics Group of Columbia, Md.
Tampa Bay Water reports that cracking has been found along about 40% of the interior lining. Problem areas are located in the soil-cement lining of the interior walls, which had been designed as an alternative erosion-control component of the reservoir.
The reservoir’s erosion-control layer consists of a layer of soil-cement that lines the structure’s interior, along with a soil wedge that lies between the soil-cement layer and geomembrane that protects the reservoir’s embankment. Black & Veatch investigated the cracking problem and found that water is becoming trapped in the soil wedge.
“The crux of the problem is the buildup of core pressures in that soil wedge,” says Jon Kennedy, manager of engineering and projects for Tampa Bay Water. “The water gets underneath the interior liner, and it’s trapped in between the soil-cement and the geomembrane cutoff wall. It’s putting tremendous pressure on that liner when we draw that reservoir down in the springtime.”
Agency officials have focused much of their public comments on HDR’s role. However, Kennedy says, “Tampa Bay Water is looking not only at the design flaw but also those who constructed the facility and those who provided the construction inspection.”
The agency is considering three different approaches for repairs: adding drains to the soil wedge and replacing the soil-cement layer; adding weight to the existing structure to prevent further movement of the soil-cement layer and soil wedge; and removing the existing soil wedge and reapplying a well-drained, soil-cement, erosion-control layer directly on top of the geomembrane.
Kennedy calls the $125-million cost “an average of a number of different repair scenarios,” and is the figure the agency is including within its Fiscal Year 2010 budget. The agency expects the repairs to start in 2012, and to last two years.
A spokesperson for HDR would only state: “HDR is fully cooperating with Tampa Bay Water to find a resolution that is agreeable to all parties. We cannot comment further at this time since litigation is pending.”