The tunnel had a fume problem from the coal-burning steam locomotives. It was built with a 1.7% (1:58.8) gradient eastbound, which was too close to the ruling gradient of 2.2%. Because of the steepness of the line, the locomotives had to pull hard to make the grade and thus burn more coal, which would lead to immense smoke in the bore. The tunnel was electrified, with the project completed on July 10, 1909, eliminating the problem. The unusual system used was three-phase AC, 6600 volts at 25 Hz, from a 5 MW hydroelectric plant on the Wenatchee River just west of Leavenworth. The tunnel section only was electrified; 4.0 route miles (6.4 km) or 6.0 track miles (9.6 km) and 1.7 percent grade through the tunnel.