DWP report: Aging iron pipes caused water main breaks

The Los Angeles Department of Water and Power released a report Tuesday discussing the rash of water main breaks that took place in September and October. The preliminary investigation indicates that many of the broken pipes were made of cast iron and had been installed 70 to 90 years ago.

Since the beginning of September, at least 70 water mains broke in and around Los Angeles, flooding streets, opening sinkholes and leaving residents without water. A break in Van Nuys sprayed a geyser 20 feet into the air, a sinkhole in Laurel Canyon engulfed a fire truck, and Coldwater Canyon Avenue was closed for five days while repairs were completed.

City officials, scientists and engineers speculated for months on the cause of these water main breaks that began in July. On Tuesday, the Los Angeles Department of Water and Power finally released a preliminary report.

The DWP report found no evidence that the breaks were caused by the three-day watering restrictions that began June 1.

The study found that many of the pipes were 70 to 90 years old. Rust, pits, corrosion and microfractures all contributed to the deterioration of the pipes, as well as graphitization, a chemical process that typically occurs under high pressure or high temperatures.

Of the pipes sampled, 77 percent were made of cast iron. These pipes tend to split longitudinally, effectively tearing them in half, rather than splitting at the seams between pipes. The longitudinal breaks tend to cause more dramatic flooding such as the Van Nuys geyser or the rupture that closed Coldwater Canyon Avenue. The DWP stated that severely corroded pipes are more likely to break this way when there is a minor increase in pressure.

The increased water levels in the Lower Franklin Reservoir this summer may also have contributed to the ruptures. The high water elevation caused a 4 pound per square inch increase in static pressure. While the DWP considers this to be within the normal range, they stated that in the past, increases in leaks coincided with increases in water levels after extended low water level periods.

The study also found that the September 5 break at Coldwater Canyon Avenue and the Sept. 8 break in Laurel Canyon may have been related. Both occurred in the same service zone and involved severely corroded water lines.

The DWP continues its plans to replace 200,000 feet of pipes per year over the next four years. They plan to specifically target pipes in corrosive soils such as those in Laurel Canyon and continue their corrosion protection program for steel pipes. They also hope to improve their ability to collect and analyze data on the condition of the pipes.

An independent group of experts is also conducting their own study of the water main breaks. The independent study's findings have not yet been released.

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