Waimanalo Wastewater Treatment Plant (HI)

A Project to Satisfy Multiple Agencies 

The Waimanalo Wastewater Treatment Plant (WWTP) in Honolulu, Hawaii, serves a rural agricultural community on Oahu and operated at a maximum capacity of 0.7 million gallons per day. The plant required additional capacity to serve new urban developments planned by the City and County of Honolulu, in addition to upgrades before the planned transfer of ownership from the State of Hawaii to the City and County of Honolulu. From inception, Parsons was mindful to coordinate and deliver a project that would satisfy multiple agencies, and we are proud to deliver it on schedule and under budget.

Parsons as General Contractor

In March 2006, the State of Hawaii’s Department of Land and Natural Resources hired Parsons as general contractor to construct the comprehensive improvements. Upgrades included the following tasks:

  • New anoxic aeration basin and solids separation tank 
  • Construct a new anoxic aeration basin 
  • Construct two new final clarifiers 
  • Construct a new solids separation tank and pump building 
  • Construct a new building for the motor control center (MCC) and backup generator 
  • Modify and improve four existing plant structures 
  • Drill and develop three new effluent injection wells

From the outset, Parsons brought an added-value approach to the Waimanalo WWTP Improvement Project. Because initial funding was insufficient for the full upgrade, we partnered with both the owner and the operator to rescope the project so work could proceed within available funding.

Additional funding became available a few months after project startup. Despite the subsequent escalation in construction costs (especially in steel and fuel), we were able to add back most of the original scope within the available funding. To incorporate the additional improvements while continuing with the main project, we reworked the budget, schedule, subcontracts, and major purchase orders while completing the difficult shoring, dewatering, and concrete phases of the project.

Extensive Resources

As general contractor, Parsons completed most of the work with in-house labor, including all of the following activities:

  • Drive sheet pile shoring 
  • Dewater 
  • Excavate 
  • Place concrete 
  • Detail and place underground process piping 
  • Install metal handrail and grating 
  • Install mechanical equipment and piping

Midway through the project, Parsons assumed the electrical work from the subcontractor in order to meet schedule and technical requirements. By drawing on Parsons’ extensive resources, we were able to construct and accelerate the challenging electrical work, which included installing and operating a 450-kW backup generator, new automated controls for both the new and existing plants, new MCC panels, and a large number of process instruments.

The upgrade to the Waimanalo WWTP automated supervisory control and data acquisition (SCADA) system is another example of our added-value approach. The City and County of Honolulu, which operates the plant, owns and operates all other wastewater treatment plants on the island. Ultimately, this new SCADA system for Waimanalo will also be installed at the other facilities. Drawing on Parsons’ knowledge of equipment, processes, and other plants on the island, we approached the new SCADA system asking, “What are the future operation plans for the city, and how do we best modify our current contract by incorporating these plans.” The challenges resolved during our work at Waimanalo will facilitate the upgrades at the other locations.

Construction Highlights

Before constructing the new concrete tanks, we drove 45-ft steel sheet piles around the tanks for shoring and dewatering. These sheet pile walls served multiple purposes:

  • Shore the earth to prevent cave-ins during construction. 
  • Allow smaller excavations, which is an important factor in existing plants because other structures, underground piping, and electrical lines are near the new tanks. 
  • Prevent groundwater from entering the excavations. The bottom tank elevations range from 5 to 15 ft below mean sea level and the groundwater table. The sheet pile coffer dam acted as a wall to prevent water from seeping into the excavation from the side. The piles were driven into a clay layer to seal the “toe” of the sheets, with the clay acting as a plug to prevent groundwater from entering the excavation from the bottom. 

To place the concrete, we used the Peri concrete forming system, which is the primary forming system for our construction group’s concrete operations because of its simplicity, increased productivity, and improved worker safety.

To reduce the cost of materials, we created precise orders by using CAD when creating process line drawings for mechanical and piping installations.

Parsons won a National Safety Council award for completing 2007 without a lost-time or recordable accident on the Waimanalo WWTP Improvements Project. Over the life of the project, Parsons had no lost-time accidents and has completed 505 consecutive workdays without a recordable accident.

When the improvements are completed on September 5, 2008, the Waimanalo WWTP will have a higher total capacity of 1.1 million gallons per day. The plant is producing very high quality effluent based on levels of biological oxygen demand (dissolved organic matter) and turbidity (undissolved solids), and it ranks as one of the top 3 of 12 plants on the island.

Repeat customers are a clear sign of effective partnerships, and our successful partnership with the City and County of Honolulu and the Department of Land and Natural Resources has resulted in several new contract awards for our construction and water groups.