Harbor Point WWTP Expansion*

The site is a filled tideland with groundwater at 4 feet, adjacent to Puget Sound and a state-designated shellfish bed. New basins must be excavated 28 feet below grade within 40 feet of operating clarifiers.

The plant discharges under an NPDES permit with tightening nutrient limits, so no tie-in can degrade effluent quality.

A secant pile wall isolates the excavation and cuts off groundwater, and a vibration and settlement monitoring system with 86 instruments alerts the team to any movement of the adjacent clarifiers. Dewatering discharges pass through a temporary treatment train before release.

Our commissioning manager has been embedded with plant operations since the first month, and each of the 23 planned tie-ins has a written process-control plan reviewed monthly with the district and the state regulator.

The project is 58 percent complete at the time of writing, ahead of the baseline schedule by 34 days, and has recorded no permit exceedances. The membrane bioreactor is scheduled for start-up in the fall of 2026.

The crew has worked more than 640,000 hours without a lost-time incident.