Federal law mandates that underwater inspections of bridges be performed every five years, but heavy flooding on the Delaware has necessitated more frequent checkups. W.J. Castle & Associates, a structural engineering firm in Hainesport, New Jersey, sends diver-engineers about every other year to look for defects, cracks, and scaling on the bridge's concrete footing. William Castle founded the company in 1983. It has 10 employees and $2 million in sales.
A century after it was built in 1904, the 1,053-foot-long span underwent a $7.7 million renovation, including three coats of "bridge green" anticorrosive polyurethane paint made by Wasser Coatings in Auburn, Washington. The company's paint is also used on the lock gates on the Panama Canal. Founded in 1988, Wasser Coatings has 20 employees and is run by co-CEOs Asher Jakabovits and Marc Schondorf.
After record floods in 2005 and 2006, the bridge commission installed a water-level sensor made by Design Analysis Associates of Logan, Utah. The device, which is attached to the side of the bridge, uses radar to measure the river's height every 15 minutes and transmits the data via satellite to the National Weather Service and other entities. William Fletcher, who founded DAA in 1971, recently sold the 25-person business to YSI, an environmental products company in Yellow Springs, Ohio.