The city broke ground Monday for the underwater portion of a project that will help transport sewage from the Ala Moana Wastewater Pump Station across Honolulu Harbor to the Sand Island Wastewater Treatment Plant in what the contractor called the most expensive microtunneling project in U.S. history.
At the center of the $118.2 million project is construction of Force Mains 3 and 4, two 5-foot-diameter polymer pipes encased in an inch of steel.
The two new mains are being built by Seattle-based Frank Coluccio Construction Co.
Already planned when a large sewage spill occurred in Waikiki in 2006, they are slated to be done by the end of 2015.
Construction began Nov. 28, 2011, on what company co-owner Franco Coluccio calls "a very large, complex project," and is about 60 percent done.
The underground portion of the 7,250-foot line, both on Sand Island and in Kakaako, is essentially complete. The Ala Moana Wastewater Pump Station is at 210 Keawe St., makai of the Gold Bond Building on Ala Moana Boulevard.
"This project is currently the longest microtunnel project to date in Hawaii, and it is the most expensive microtunnel project in the country that’s ever been performed … with the size and the magnitude of the depths of the shaft, length of drives (and) diameters," Coluccio said.
Microtunneling involves the boring of tunnels through laser-guided remote control.
The project will cross under 1,600 feet of water, going 100 feet below the soft sediment of the state’s busiest harbor. The project is using 100-foot-deep microtunneling shafts that are being constructed utilizing a sophisticated technique used for only the second time in the U.S., city officials said.
Monday’s groundbreaking for the underwater portion was held at Sand Island State Recreation Area eight years to the day after a major Waikiki sewage spill that occurred after a 42-year-old water main ruptured. That required approximately 48 million gallons to be discharged into the Ala Wai Canal to avert raw sewage backing up into hotels and residences.
Some of the island’s most popular tourist beaches were forced to close as a result of unacceptable bacteria levels.
The Ala Moana force main project is part of the city’s consent decree reached in 2010 with the U.S. Environmental Protection Agency to resolve violations of federal and state law for a series of sewage spills, including the 2006 Waikiki incident. It requires the city to complete more than $4 billion in improvements to its sewage collection and treatment systems over 25 years.
Once Force Mains 3 and 4 are online, the concrete, 1950s-era 60-inch Force Main 1 will be closed permanently, city officials said. The existing Force Main 2, built in 1983, will be used as the primary line alternately with Force Mains 3 and 4 during normal flows.
A second of the three will be used to deal with overflow during heavy rainstorms, while the third will provide emergency backup.
Mayor Kirk Caldwell said redundancy in the system will make it much less likely there will be a repeat of the 2006 spill.
"We are rebuilding our sewer system for the 21st century, so that this island can thrive for another 100 years," Caldwell said. "And it cannot thrive if you have a sewer system that is antiquated and is designed for a place with a much smaller population."
The Ala Moana pump station system is the largest on Oahu and handles all wastewater generated from Niu Valley to Nuuanu, serving about half of the island’s population, the city’s 2010 environmental assessment for the project said. The average daily flow rate through the system is about 48 million gallons, the study said.
During rainy periods the flow can increase to more than 120 million gallons per day.
