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Human error, increased pressure in main blamed for Chapel Hill water emergency

Posted February 10

— A week after Chapel Hill schools and businesses were forced to shut down because of a combination of a water main break and a treatment plant shutdown, officials with the Orange Water and Sewer Authority have identified the causes of the crisis.

OWASA had to shut down the Jones Ferry Road Water Treatment Plant on Feb. 2 because of fluoride levels in the water were almost 50 percent above allowed levels. A report by an outside consultant said a plant operator accidentally hit a button that caused excess fluoride to be pumped into the system, and the error wasn't corrected for more than three hours.

The operator was by himself for several hours that day because another staffer had training and a dental appointment, and the operator also had to oversee contractors at the plant, so his attention was divided, according to the report.

The following day, a 12-inch water main near the intersection of Summerfield Crossing Road and Foxcroft Drive failed, spewing out about 1.2 million gallons of water.

Another outside consultant said the treatment plant problem might have played a role in the water main break because OWASA's altered pumping pattern may have increased the water pressure in the line. But the more likely cause was increased pressure from outside, such as heavy trucks repeatedly driving over the intersection where the break occurred. The consultant noted the main was made of rigid material, was only 3 feet below the street and was no more than 8 inches over a stormwater pipe, meaning it could have cracked after being compressed too many times.

About 80,000 water customers in and around Chapel Hill had to use bottled water for almost two days before water pressure returned to normal last Saturday and tests should no bacteria in the system.

OWASA officials apologized Thursday for the disruption in service and the headaches it caused and promised to rebuild customers' trust and confidence in the water system.

The board of directors is expected to hold a special meeting next week to discuss the consultants' reports and devise strategies to ensure the problems don't happen again.

2 Comments

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  • John Kramer Feb 10, 2017
    user avatar

    Thank you, James Dodson for the analysis. Maybe WRAL should change their headline based on your facts.

  • James Dodson Feb 10, 2017
    user avatar

    This is not entirely true!! Read the report, it plainly says this was caused by a combination of problems and the root cause was equipment failure. The operator made a process change due to changing demands during testing of a raw water main. The initial change in fluoride dosing was an error, but the operator corrected that error 12 seconds later and the pump failed to respond to the command unbeknownst to the operator. If you really read the report, you'll also see the outside consultant contacted the pump manufacturer to question why this would happen. Here is a quote from the report: "In discussions with the chemical pump manufacturer’s authorized repair center representative, the
    observed condition of pumps ramping up to a higher speed after receiving a new lower flow set point
    (e.g. 4% after being at 80%) “…is not a normal operation.” The representative’s theory is that this
    condition “would likely be caused by a control board (internal to the pump) problem.”