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We are not able to say with certainty the exact cause of most water main breaks. We do know that there are several factors that contribute to water main breaks: age of pipe, type of pipe, soil and construction conditions when the pipe was installed, and temperature.
Pipe age and type: We find that post World War II cast iron pipes in our system made between 1945 and 1955 have a higher occurrence of failure. Cast iron pipes accounted for 70 percent of our repairs and breaks since 1992, but made up 80 to 85 percent of our repairs and breaks in the past five years. Other cities with similar pipe vintage have similar pipe failure rates.
Temperature: As temperatures move in and out of freezing, it’s not uncommon to see breaks occur.
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Nov 2015: 7 / Nov 2016: 1 Dec 2015: 2 / Dec 2016: 10 Jan 2016: 2 Feb 2016: 1 Mar 2016: 2
Since 1992 we’ve averaged 23.3 breaks or repairs per year. In 2015 we had 23 breaks; in 2016 we also ended with 23.
Depending on the type of break, it may be repaired or a section of pipe may be replaced completely. Once the break is repaired or replaced, crews will backfill the excavated site, pouring fill material from a dump truck and evenly distributing and compacting it on the work area. We will watch the repair site for a couple of days, and, then Streets crews will restore sidewalks and road surfaces to original condition. Cleanup of debris on yards and roadways is usually the same day as the break, provided we do not have freezing conditions.
The water in the pipe gets flushed through and is then disinfected for delivery. We do have a distinct process for bringing a main back in service to meet our water quality and purity standards. We flush and also provide contact time with a chlorine disinfectant. We will not reopen customer services until our water has no turbidity and meets the appropriate water quality standards.
The Public Works budget accounts for the need to staff unexpected events. The nature of our work involves responding to unplanned circumstances that demand immediate attention. Crews are accustomed to responding on an on-call basis.
The City has a two-prong plan to proactively address potential water main breaks. We gather and analyze data on main breaks to project what sections show a propensity to break and prioritize replacement based on that. Our Maintenance division performs routine pipe replacement, blocks at a time and uses city crews and small works contractors. Our Engineering division develops those projects with a larger scope, fitting them into our Capital Improvement Program. The current Water Main Q project from Pacific to 35th on Broadway Avenue is an example of one of these larger water main replacement projects.