Summary of Project Merits
The Ala Moana Wastewater Pump Station (AMWWPS) facility is comprised of two pumping stations, known as AMWWPS 1 and 2. The AMWWPS facility is the largest wastewater pump station operated by the City and County of Honolulu (City), conveying over 45 million gallons per day (mgd) from the urban core of Honolulu to the Sand Island Wastewater Treatment Plant.
Per a United States Environmental Protection Agency (EPA) Global Consent Decree (GCD), the City was required to complete specific improvements at AMWWPS 2 by December 31, 2020, and selected Brown and Caldwell (BC) to plan and design the AMWWPS Upgrade Project under an accelerated schedule.
This rehabilitation project increased reliability, redundancy, and fexibility at the City’s most important pump station, protecting public health and safety by reducing risk of a wastewater spill in the heart of Honolulu. The pumping capacity was increased to over 180 mgd with redundant pumps and force mains available. Located in Kakaako, the upgraded facility also supports Transit Oriented Development for the upcoming rail transit project. Key project objectives included:
• Increased pumping capacity at AMWWPS 2 to support future flow projections and increase pumping redundancy
• Implemented surge mitigation measures at AMWWPS 2 to improve reliability
• Rehabilitated the ventilation and air conditioning systems at AMWWPS 2 to improve energy efficiency and meet updated fire and energy codes
• Upgraded electrical and instrumentation systems at both AMWWPS 1 and 2 to meet updated City standards and improve facility monitoring and control
Much of the existing components were outdated or beyond its useful service life. The improvements contribute to a dependable facility for years to come.
Construction of this $14.5 million rehabilitation project started on March 25, 2019 and needed to be completed within 21 months to meet the GCD deadline. Two construction milestones were specified to optimize the available construction duration.
Milestone 1: GCD Improvements
• Priority work tasks including the AMWWPS 2 pump system, surge mitigation, electrical, and instrumentation improvements. This work was required to be complete
by the GCD deadline.
Milestone 2: Supporting Improvements
• Non-priority work tasks including AMWWPS 1 electrical and instrumentation improvements and AMWWPS 2 ventilation system rehabilitation and roof repair. These additional supporting improvements contribute to the reliability of the facility.
The original schedule was tight with minimal float, and the last nine months of construction were further complicated with the impact of the COVID-19 pandemic and the storm flow threat of Hurricane Douglas in July 2020. Representatives from key equipment manufacturers were unable to conduct scheduled performance tests when travel restrictions to Hawaii were implemented starting in March 2020.
Although Hurricane Douglas did not bring severe storm flows, the storm preparation activities impeded the construction schedule by requiring pumps to be available for emergency use that were scheduled to be out of service.
Construction activities were delayed to prioritize storm preparation. Collaborative and creative efforts between the City, construction manager, contractor, equipment manufacturers, and designer were required to overcome an unprecedented challenge to meet the GCD deadline, completing the
commissioning period with two days to spare. These efforts included contingency planning to return pumps to service in an emergency; scheduling and commissioning sequence modifications; and assuring contractor operations support, all while maintaining testing and quality.
In addition to schedule challenges, construction sequencing required careful coordination with City operations to ensure the facility was not at risk or disrupting normal City operations. The AMWWPS facility had to remain operational and be capable of conveying storm flows at all times throughout construction.
While AMWWPS 1 could manage daily dry weather flows, the facility needed 3 of the 4 existing AMWWPS 2 pumps to meet the modeled 5-year, 6-hr storm and historical peak flow exceeding 160 mgd. Because replacing multiple pumps at one time was infeasible, each individual pump installation had to be thoughtfully sequenced with City operations. The first step to reduce risk was to install a new 5th pump at AMWWPS 2, which provided much needed additional capacity for the remainder of construction.
The project also required coordination of numerous facility outages to cutover operations from existing to new equipment incrementally. Facility outages had several constraints imposed on the Contractor to sustain adequate, uninterrupted pumping capacity during construction. Weekly weather forecasts were also used as a criteria for outage approvals, and specific outage durations were prescribed for specific activities depending on the risk.
Aside from construction challenges, the new AMWWPS facility provided robust features to enhance reliability. For a pump station of this physical size and capacity, a surge event (water hammer) caused by a sudden loss of power would be especially damaging. Water hammer could rupture piping and damage equipment, potentially leading to a wastewater spill. A surge analysis was conducted to simulate flow conditions under a power failure and to assess alternatives to mitigate potentially damaging surge pressures. One of the key objectives of the GCD was addressed by the selection of a mechanical flywheel for its reliability, simplicity, and effectiveness.
Sized based on modeling results, a flywheel requires minimal maintenance compared to other surge mitigation measures. This mechanical device is coupled to the pump shaft, increasing the moment of inertia of the rotating pump.
Upon a power failure, the rotational energy of the flywheel prevents the pump from stopping too quickly, allowing the pump to decelerate gradually to prevent a surge event. The flywheel was designed for installation on the existing intermediate floor within the WWPS that did not impede on the limited facility footprint and did not require structural improvements. A structural analysis of the intermediate floor was conducted to determine whether the floor had adequate strength for the weight and movement ofthe flywheels.
Additional work is ongoing to support the City’s improvement of the current Supervisory Control and Data Acquisition (SCADA) system and optimize control strategies in coordination with the AMWWPS facility improvements.