Intake Fouling Assessment and Mussel Cleaning via Design-Build Swabbing and Pigging Operation at Toronto Water's Island WTP

摘要

The Island Water Treatment Plant ("WTP") is serviced by three high-density polyethylene ("HDPE") pipes, each 1.6 m in diameter, conveying raw water from 5.3 km offshore at a depth of 83 m, where the water temperature is a constant 4°C. In 2014, a remotely operated vehicle ("ROV") inspection revealed that the intake pipes were coated in quagga mussels, with interior coverage ranging from 20% on-shore to 100% off-shore. In the fall of 2018, a design-build construction tender called for a "progressive pigging" methodology to clean the three intakes over a 60 day period. Contractual performance was based on C-factor restoration, wherein the pigging operation was to have restored 90% of 2004 pipe commissioning baseline range of 132-139. Pre-pigging 2018 C-factor values ranged from 99-103. After-pigging C-factor values ranged from 130-139. Data collection methods had some intrinsic variation due to different pump selections, but the overall magnitude, supported by ROV visual inspection, concludes that the raw water intakes were cleaned to an above-acceptable contractual performance level, fully recovering the pumping station hydraulic capacity established during commissioning.