Protecting Paradise From Sewer Overflows

Honolulu makes huge investment to improve its collections system and protect coastal waters.
Protecting Paradise From Sewer Overflows
Lori Kahikina, Director Department of Environmental Services City and County of Honolulu, Hawaii

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Great beaches, fresh trade winds, big surf and a fascinating culture make Hawaii a very special place. In turn, the popularity of the islands, its climate and geology create special issues for wastewater collections.

In the City and County of Honolulu — now home to more than 1 million people — urban density, aging sewer lines and heavy rainfalls have led to wet weather sewer overflows and spills, some of which have closed the area’s popular beaches. Hurricanes and other tropical storms can triple the amount of wastewater that normally flows through the system to the island’s treatment facilities.

But now, under terms of a 2010 consent decree, the city’s Department of Environmental Services (ENV) is taking action — including construction of large tunnels that will provide additional sewer capacity and replace the existing force mains, and implementing other measures to minimize the discharge of untreated wastewater. Overall, the price tag for the various projects is expected to reach $5 billion.

“Honolulu is a very confined area,” explains ENV Director Lori Kahikina, P.E. “We have easement issues with lots of sewers located beneath buildings. The soil is volcanic and close to the ocean, so we experience a lot of inflow and infiltration, and high salinity counts.”

The first of the tunnel systems and its auxiliary components is scheduled to be completed this spring, with the second scheduled for commissioning in June 2018.

The system

Kahikina’s department is responsible for wastewater collections, treatment and disposal, as well as solid waste management, for essentially the entire 600-square-mile island of Oahu. A few privately owned systems serve military bases, small developments and the residential community of Hawaii Kai.

The overall sewer system extends for 2,100 miles and includes 70 pump stations. Much of the flow is by gravity. Sewer lines “run the whole gamut of materials,” Kahikina says, including old terra cotta lines from the last century, HDPE and reinforced concrete. Some of the older lines contain asbestos pipe. The lines range in size from 6 inches to 10 feet in diameter.

The department employs about 170 people in the collections division and manages an annual operations budget of around $24 million.

The Honolulu team uses about a dozen Vactor combination trucks to clean the system. “They’re our workhorses,” says Kahikina, explaining that they are used mostly for road-accessible lines and clean-outs. “For smaller lines in easements, we use mechanical rodders. Those are our two main technologies.”

The rodders are also used to cut and remove root growth — a common problem on the island.

The consent decree mandates that every mainline collections system asset be inspected and cleaned at least once every five years. Honolulu uses Aries Industries, CUES, RedZone and UEMSI equipment to meet that requirement.

Problem laterals are inspected more often and if there are roots or broken pipes on the city’s side, then cleaning and repairs are undertaken immediately. If the issue is on the property owner’s side, Kahikina’s department issues notices to the owners to have the deficiency corrected.

An ICOM3 asset management software system from RedZone Robotics drives the cleaning and maintenance program. The department also employs a GIS system, supported by Oracle and Esri software.

Special circumstances

Kahikina says Honolulu is simply forced to live with some of the special challenges faced by the sewer system. Easements and lines under buildings are examples. “We’re pretty much stuck with those,” she says.

But on other fronts, her department takes an aggressive approach. Where roots have infiltrated the lines or salinity has caused pipe deterioration, Honolulu is using CIPP technology to line old pipe structures. Trenchless replacement is the choice wherever possible, because the density of buildings often makes open-cut installation difficult.

Kahikina explains that Honolulu uses IDIQ (Indefinite Delivery, Indefinite Quantity) contracts, inviting qualified contractors to bid on a package of line items that might be scheduled out over a period of time. “It’s like the federal procurement process,” she says. “The low bidder has the right of first refusal.”

The department’s crews pay special attention to the system’s 70 pump stations. “We have a lot of grease and rags,” Kahikina says. “It’s unbelievable what people flush down their toilets.” As a result, operators are cleaning pumps almost constantly, she says.

Periodic maintenance is also dealing successfully with spills that used to be common along the smaller, 6- to 8-inch sanitary sewer lines that fan out across the island. Spills have dropped from 200 per year in 2006 to the mid-60s in 2014. She credits increased periodic maintenance of the lines, directed by Frank Doyle, chief of the collections division, for the significant improvement.

The tunnels

The new force mains first pass under Honolulu Harbor at a depth of 30 feet below the harbor floor (approximately 90 feet beneath the ground surface) and connect the two large pump stations serving the vast majority of the east side of Honolulu with the Sand Island Wastewater Treatment Plant. When finished, the project will provide redundancy and flexibility in operations, including 7,000 feet of dual 60-inch steel casing with plastic pipes. About 1,600 feet of the new line will be below the Honolulu Harbor entrance.

The new lines, says Kahikina, will give Honolulu needed flexibility and redundancy.

“Two force mains will be available at any time to handle peak flow,” she says, with one in reserve, in case of a force main failure. That’s what happened in 2006, when a force main broke and allowed 48 million gallons of wastewater to spill into the Ala Wai Canal.

The original force main will be decommissioned.

The city’s Department of Design and Construction is working with Frank Coluccio Construction of Seattle to complete ancillary work related to the force main. The two force mains were completed in August 2015, and work is now proceeding on valving. The cost is about $118 million.

The second dig is not as far along but will also have a positive impact on overflows when completed. Called the Kaneohe-Kailua (K-K) Tunnel, it will convey wastewater by gravity from the Kaneohe pretreatment facility to the Kailua Regional WWTP, a distance of 3 miles. The new line will also provide storage capacity for excess wastewater, further mitigating against spills and overflows. It will replace an older force main that had been subject to numerous breaks.

Kahikina says Honolulu successfully negotiated with the EPA to build the 10-foot-diameter gravity sewer line rather than construct a redundant force main — a more expensive plan called for in the original design.

Contractor Southland Mole Construction of Kaneohe, Hawaii, is boring the tunnel at a diameter of 15 feet from a depth of 35 feet below ground level at the head end of the tunnel to a depth of 82 feet at the other. A major lift station will bring the water to the surface for treatment at the Kailua Regional plant. The project, which will cost about $174 million, includes odor control, entry shafts, diversion structures and a storage reservoir.

Consent decree

A second phase of the consent decree, signed in 2010, calls for installation of secondary treatment at both the Honouliuli and Sand Island WWTPs. The 26 mgd Honouliuli WWTP, which is partially secondary now, will be required to provide full secondary treatment by 2024, and the 62 mgd Sand Island WWTP by 2035. Previously, both facilities have operated under permits allowing variances from full secondary treatment.

The upgrades will be costly. The city estimates the total for improving treatment at both plants to be $1.7 billion.

At the beach

The last thing a popular vacation destination like Hawaii needs is beach closings. Unfortunately, that’s happened twice in the last 10 years and is a major factor in the massive wastewater overflow control program the City and County of Honolulu has embarked upon.

In 2006, roughly 48 million gallons of untreated wastewater spilled into the Ala Wai Canal after a force main broke beneath the street. According to media reports, the spill triggered health concerns and closed several beaches in Waikiki.

And last August, as Honolulu was engaged in the first phase of its $5 billion program to reduce overflows and spills, heavy rains spawned by tropical storm Kilo caused about 500,000 gallons of wastewater to be discharged from manholes and flow into the park and storm drains that lead to the ocean. Tourists and the general public were advised to stay out of coastal waters for several days.

“Once the ancillary work is completed, the city will have redundancy and flexibility to send the excess flow during heavy rain events from the metro region area to Sand Island WWTP,” says Lori Kahikina, P.E., director of the city’s Department of Environmental Services.


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