The sounds of progress start echoing through the State Route 520 Pontoon Construction project site this week as crews begin to drive hundreds of support pilings to form the foundation of a pontoon casting facility. The Washington State Department of Transportation and contractor Kiewit-General are constructing the foundation for the casting basin where they will build the concrete pontoons that will form the backbone of a replacement SR 520 floating bridge. Crews must drive as many as 900 steel piles 125 feet into the ground. During the three-month process, K-G will have up to 20 pile drivers working at the site, and nearby residents and businesses will notice hammering sounds. The cylindrical piles are 18 to 24 inches in diameter and measure 140 feet long. Laid end to end, the 900 piles would stretch nearly 24 miles.