Steve Hrvoich stood in the year-old valley beneath girders for the new northbound bridge on Interstate 79 on Thursday as gigantic dump trucks known as triple 7s whizzed by, hauling up to 100 tons of dirt each from the east side of the highway to the west. Crews for Walsh Construction II were a few days away from completing what Mr. Hrvoich, the construction engineering manager for the Pennsylvania Turnpike, called “the big eastern spread.” The crews moved 2 million cubic yards of earth from the eastern side of the valley, clearing space to install thousands of feet of drain...