As one of the first steps in the retrofitting process, workers removed the existing concrete floor.

Workers install one of the steel casings for the cement support piling. The pipes in the foreground were part of the dewatering system that reduced the effects of hydrostatic water pressure. Pumps were also installed to prevent water from seeping into the excavation site.

During the first stage of excavation, workers removed 23,744 cubic yards of dirt reaching 5-ft deep. The walls were reinforced as the depth increased.

Dewatering pumps are shown here behind the 3- by 10- by 9.5-ft oak beams that were used for wall reinforcement.

To provide angled support, tiebacks (0.6-in. diameter cables) were installed in 60-ft deep, 12-in. diameter holes which were then filed with cement.

The second stage of excavation.

Once excavation was complete, workers installed 689 tons of steel rods to reinforce the floor. Drain pipes within the steel mesh relieve hydrostatic pressure. Cement was poured through the steel to reinforce the floor.

The NBL's water proofing system consists of polyethylene sheeting, protection board and water barrier layers.

Some 645 tons of steel rods reinforce the pool walls. Wall forms were put into place to form the lower concrete walls of the pool.

Workers poured concrete for the upper 20 ft of the wall in sections using braced wall forms and steel reinforcing rods.

The pool was complete on Dec. 20, 1995, two weeks ahead of schedule.

CONSTRUCTION STATISTICS Excavation (dirt)641,088 cu ft 23,744 cu yards Wood lagging 3" x 10" x 9' oak timbers 1,782 timbers total Reinforcing steelFloor: 689 tons (1.378 million lb) Walls: 645 tons (1.29 million lb) Steel tie wire310 miles Concrete floor6 ft thick 5,300 cu yards 10,303 tons ( million lb) 530 concrete truck loads Walls5-ft thick below ground 2.5-ft thick above ground 3,500 cu yards 6,979 tons 350 concrete truck loads Water6.2 million gallons 25,823 tons ( million lb) Filtered at 5,400 gal/minute Heated to 86 degrees F