Critical wastewater infrastructure in Honolulu has reached a major construction milestone, with Phase 1 of the Sand Island Wastewater Treatment Plant’s secondary treatment upgrade completed after five years of construction. Hensel Phelps delivered the project three months ahead of schedule while maintaining operations at the active treatment facility.
The project required extensive construction activities within an operating wastewater treatment plant. Work included deep excavation and dewatering, auger-cast-in-place pile installation, cast-in-place concrete structures, underground utilities, electrical infrastructure, process equipment and mechanical and process piping ranging from 1.5 inches to 96 inches in diameter.
Connecting new systems to existing plant infrastructure required detailed sequencing and coordination. Construction activities and system tie-ins were planned to limit disruptions to ongoing treatment operations while allowing work to progress safely.
The project included new and upgraded treatment infrastructure supporting the plant's secondary treatment capabilities, along with associated process, mechanical and electrical systems.
Hensel Phelps used Virtual Design and Construction tools to coordinate the project's multiple disciplines and identify potential conflicts before installation. Laser scanning helped project teams verify existing conditions and refine piping layouts, while drone mapping supported site documentation and construction planning.
Hensel Phelps also self-performed more than half of the project's work. Approximately 1,400 people contributed more than 1.2 million work hours, with 109 trade partners and vendors and approximately 350 suppliers and service providers participating in the project.
As the facility moved into clean-fluid startup, Hensel Phelps provided six months of continuous coverage to support testing, commissioning and integration of the new systems. The effort included night, weekend and extended-shift work.
A data-driven activated sludge seeding strategy was also used to accelerate the startup process. The approach supported the transition into operation and contributed to the project's early completion.
The City and County of Honolulu marked the milestone with a grand opening and blessing ceremony on Aug. 11, 2026.
The Sand Island project highlights the coordination required to modernize essential wastewater infrastructure while an existing treatment facility remains operational. The project also demonstrates how digital coordination, self-performed work and commissioning strategies can be integrated into complex infrastructure construction.
For owners planning upgrades at active utility facilities, maintaining operations while introducing new systems requires detailed sequencing and coordination from construction through startup.
Source: Hensel Phelps.
