The ACEORP tunnel is in the Tumuning area. The water level in the tunnel was monitored from 1955–65 and from 1973–present but only data after 1982 are available in digital form. The tunnel is dug to the water table and consists of an inclined shaft, three skimming tunnels, and a large pump room. Tunnels 1 and 2 are 150 ft each and tunnel 3 is 700 ft in length. This station is operated by the Honolulu field office and is equipped with a shaft encoder and data logger.