 The transformer house was "built on the upper river, above deep excavations housing twenty-one generating units.Tailwater from the generators passed into a 7000-ft tailrace tunnel, which conveyed the water beneath the city to the lower river, near the present-day site of the Rainbow Bridge.The 18-ft by 21-ft tunnel required over 3 years to build, used more than 16 million bricks in a four-course lining.