This hollow concrete caisson was constructed under Phase 1 of the raw water intake project for the new water treatment system construction required by the Flood of 1997. The massive caisson is 60 feet in diameter with a 3'-6" sidewall. The 6'-3" thick finished floor of the caisson is 65 feet below grade and is supported on 37 - 24" diameter augered grout injected piles. The caisson will be the foundation for an 80 foot wide by 50 foot high two story pump station under Phase 2. After consideration of various high tech systems to construct the project at such excessive depths, the contractor chose a system where the caisson would be cast above grade and allowed to settle into the ground with its own weight as soil was excavated from below.