AC Enigma: Using Opportunistic Sampling to Assess Asbestos-Cement Water Main Performance in Winnipeg

With a population of over 680,000 people, the City of Winnipeg is the eighth largest city in Canada. To support this user base the City maintains an inventory of over 2,900 km of water mains, consisting of cast iron (~30 %), asbestos cement (~27 %), PVC (~33 %), and prestressed concrete pressure pipe (~5 %). Historically, the City focused its investment on the replacement and cathodic protection of cast iron mains, which due to highly corrosive soils had experienced extreme deterioration. Consequently, very little was known about the condition of its remaining system, leaving the City exposed to risk and uncertainty over coming planning horizons. Wishing to improve its understanding of material performance and ability to target current and future water system investments, the City worked with UMA Engineering Ltd. to undertake a Water Main Criticality Assessment Study. One component of this project was to undertake an assessment of the City's asbestos-cement (AC) water main inventory. Winnipeg's first AC water mains were installed in 1932, at a time when AC pipe was being introduced to North American markets. Early studies found that they performed well in Winnipeg's aggressive soils, which resulted in widespread adoption and use of AC within the city until the early 1980s. While some work was done to assess the impact of water chemistry on internal pipe wall degradation, very little was known about the long-term performance of the lines, and the risk and liability they might pose. Seeing to address these concerns, an AC Sampling and Testing Program was developed and introduced. Under the AC Sampling and Testing Program, pipe segments were collected opportunistically from in-service water mains throughout the city and subjected to an array of destructive and non-destructive test procedures. Data was collected and analyzed to assess the current risk posed by the City's AC inventory, and to extrapolate long-range system performance. This paper reviews techniques used in the collection and testing of pipe samples, presents findings from the analysis of current and long-term performance, and discusses the challenges faced in introducing a standardized AC sample collection and testing program in the City of Winnipeg.