Ralph L. Wadsworth Construction installed 1,000 caissons ranging from 18 inches to 60 inches in diameter to expand Concourses B and C. Caissons were installed to depths of 40 to 60 feet. Drilling for caissons presented unique challenges during the season of daily thunderstorms in the Rocky Mountains. Crews timed the drilling of each hole, starting work before sunrise, so that holes could be filled with concrete before the storms rolled in each afternoon.