To meet demand, TBW drew down the reservoir to slightly more than two billion gallons by fall 2007. However, as early as December 2006, significant cracking began.
HDR had designed the reservoir's interior with a geomembrane layer at its base, followed by a section of compacted soil and then a 16-in.-thick flat-plate soil-cement liner at the upper level.
There was no drain system built into the soil-cement wedge. The specified normal drawdown rate of 66 mgd could be achieved by gravity draining, and the embankment's soil-cement layer would function, though both HDR and TBW knew it would crack.
Gerald J. Seeber, the utility's general manager, noted as much in a 2008 letter to nearby residents explaining why the reservoir was in no danger of collapse.
"We expected the soil cement lining to experience some cracking; that is the nature and makeup of the material," Seeber wrote. In the letter, Seeber estimates the area of cracks to equal "about 5 acres of the 80 acres of [soil-cement] material."
The utility contends the problem goes beyond normal cracking. It points to a report by Black & Veatch—hired to investigate the causes of the cracking—that suggests the problem is caused by increasing pressure in the soil-cement wedge. As the water in the reservoir recedes, the theory goes, the water in the soil wedge remains stuck at higher levels, which eventually leads to cracking.
Black & Veatch's theory "doesn't hold water," Connolly says. In fact, he says, HDR discovered data that show no buildup of pressure in the soil wedge.
Still, says Kennedy, "The bottom line is, they did not provide a drain for that soil wedge. We have two million cubic yards of dirt that doesn't give up its water."
Despite the cracks, TBW has regained the full permitted use of the facility since finishing repairs in 2009.
Fuss Over a Fix
Originally, in addition to HDR, Tampa Bay Water sued the construction manager, Columbia, Md.-based Construction Dynamics Group (now part of ARCADIS), along with Barnard Construction Co. and its embankment subcontractor, McDonald Construction Corp.
It settled with CDG for $6 million. The utility also settled with Barnard, for $750,000. As part of its agreement with Barnard, the contractor remained a party to the suit and liable for up to $5 million, pending the trial's outcome.
