Board of Water Supply. City Water Tunnel No. 1. A portable drill rig collects core samples of the rock deep below upper Manhattan. These borings helped geologists and engineers to determine the best route for the 18-mile City Water Tunnel No. 1. The rig is set up near 156th Street and the Harlem River Speedway, originally built for horse racing and replaced by Harlem River Drive in 1964. July 20, 1910.