Anacortes Water Treatment Plant Improvements
The city of Anacortes' new Water Treatment Plant (WTP) is the sole supply of potable water for the city and its wholesale customers, including two large oil refineries, a major naval air station, and two other municipalities. The water source is the Skagit River, which has wide variations in sediment levels and is prone to flooding. The city initially contracted HDR to design improvements to the existing WTP to improve treatment performance for continued compliance with the latest drinking water regulations, improve reliability, and increase production capacity from 30 to 42 million gallons per day (MGD) with provision for future expansion to 55 MGD.
The preliminary condition assessment revealed that all existing structures fell well short of current building code requirements, particularly in regards to vulnerability to floods and earthquakes. All major electrical power distribution and pumping systems were below the anticipated new FEMA 100-year flood elevation and highly susceptible to damage and major production interruptions.
In the treatment process the flocculation/sedimentation system performance did not achieve design treatment level at the maximum design flow capacity and/or when raw water turbidities were elevated, which occurs frequently, and the existing clearwell capacity was significantly undersized for meeting chlorine disinfection requirements. Based on these assessments, the city determined that an all-new treatment plant would best meet their goals.
The new plant includes a high-rate ballasted sedimentation pre-treatment system, granular media filters, intermediate and finished water pumping stations, a chemical building and feed systems, a 2.1 million gallon clearwell, improvements for residuals streams handling, a standby power generation station, and an all new SCADA system. All critical equipment for plant operation is set above the anticipated FEMA 100-year flood elevation. Standby power is provided by three 1,250 kW diesel-engine generators with on-site fuel storage for up to seven days of operation.
- Installed state-of-the-art high-rate ballasted sedimentation system for enhanced pre-treatment performance
- Increased capacity to 42 MGD
- Set critical equipment at an elevation above the anticipated FEMA 100-year flood elevation
- Installed standby power generation station enabling continuous plant operation at production rates of up to 21 MGD