Peel Back the Layers on a Critical Feedermain Assessment and Repair Project

Over the past 15 years, the Region of Peel in Southern Ontario has been developing an extensive condition assessment program for its large diameter prestressed concrete cylinder pipe feedermains. The proactive assessment and repair of critical feedermains helps assure that the Region can deliver safe and reliable drinking water to its customers every day. The Herridge 1,500-mm (60-in.) feedermain is approximately 6 km (3.7 mi) in length and was first assessed using electromagnetic inspection technology in conjunction with a visual and sounding inspection in 2011. This inspection identified a significantly higher-than-average degradation rate for prestressed concrete cylinder pipe (PCCP), with 6.2% of pipes exhibiting signs of broken prestressing wire wraps, particularly along a critical trucking route with heavy traffic loading and an adjacent rail corridor. From 2014 through 2016, the Region undertook an extensive repair program of the Herridge Feedermain, repairing 106 pipes throughout the length of the feedermain with carbon fiber reinforced polymer (CFRP). Repairs were completed before the introduction of American Water Works Association C305 standard and included both composite and stand-alone designs to reinforce distressed pipes. A follow-up electromagnetic and visual and sounding inspection in 2021 also included a detailed inspection of the CFRP repairs to assess their long-term durability. The electromagnetic inspection confirmed continued high rates of degradation, with 6.2% of all pipes exhibiting signs of broken prestressing wire wraps in 2011, and an additional 2.8% exhibiting signs of broken prestressing wire wraps in 2021. Inspection of the CFRP repairs concluded that the stand-alone designs had held up well; however, structural issues were found in several composite repaired pipes as well as new pipes. This led to upgrades in 2022 for the damaged and most at-risk composite pipes to the stand-alone design to increase the expected lifespan of the repairs. Additionally new repairs were completed for a handful of pipes that had experienced new or growing amounts of broken prestressing wires since 2011. The 2021 condition assessment also featured the addition of inspection and maintenance on all in-line butterfly valves in the feedermain, including entering the pipe where possible to inspect the valve gaskets and seats. The valve maintenance program ensured that valves are operable in an emergency and was completed at a fraction of the price of valve replacement. The Region’s long-term management of the Herridge Feedermain, including electromagnetic inspections, planned CFRP repairs during future outages, and valve maintenance program is helping to achieve system reliability and honor the commitment to customers of delivering clean, safe drinking water.