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It took nearly three hours from the time the alarm went off Wednesday night in Houston before Chevron discovered that crude oil was overflowing from a concrete vault housing pipeline valves near the entrance to Red Butte Garden.

And that raises questions.

Should Chevron have found the leak sooner, especially given that six months earlier a puncture in the same pipeline spilled 800 barrels of crude into nearby Red Butte Creek?

And should the company have notified Salt Lake City immediately after the alarm signaled a possible problem instead of waiting three hours until it found the leak?

"Clearly, with the city still dealing with the effects of the first disaster, we expect immediate notice of even the slightest monitoring anomaly related to that section of the pipeline," Salt Lake City Mayor Ralph Becker said Friday.

Yet, for Chevron, it isn't that simple.

"It isn't unusual for us to get alarms signaling there might be a problem on a pipeline," Chevron spokesman Dan Johnson said. "Sometimes we might get one a month on a particular pipeline, while other times we might get two or three in a week."

About 95 percent of the time, he said, they turn out to be false alarms.

When the alarm sounded at 8:30 p.m. Wednesday in the company's pipeline-control center in Houston, it had no way of knowing. Yet the alarm — warning of a possible problem with the flow of crude or a loss of pressure on the Salt Lake City pipeline — was concerning enough that Chevron personnel remotely shut it down.

In Salt Lake City, Chevron then quickly began assembling its emergency-response crews, calling them back into work. Once gathered, the six-member team started walking and slowly driving along the route of the buried pipeline that winds its way under the city's streets from the refinery east toward the mountains.

"Our first priority was to make sure there wasn't a leak that might impact people living in the city," Johnson said. "From there, we started looking at places like the valve stations. And that was when we found the leak."

At 11:23 p.m., Chevron reported the leak to the Salt Lake City Fire Department. Hazardous-materials workers and firefighters, assisted by Chevron personnel, raced to build earthen berms to contain the spill — which, as it turned out, dumped up to 500 barrels of oil 100 yards from the site of the larger June 11-12 leak.

Johnson argues that, with the high degree of pipeline false alarms, it makes sense for Chevron to establish that there is a problem before notifying local emergency personnel.

"We could give them a call every time we get a signal that there is an anomaly on our pipeline," he said. "But, given the false alarms that we get, it wouldn't be too long before they stopped paying attention."

Jeff Niermeyer, Salt Lake City's director of public utilities, said a fine line needs to be walked.

"Obviously, we want to know when there is a problem as soon as possible so we can react," he said. "But we also don't want to find ourselves in a situation where we are reacting and there isn't a problem."

If Chevron can be criticized for its response to the latest spill, Niermeyer said, it would be if it turned out the company wasn't using the best technology available to shorten the time it takes to determine if a leak occurred.

"I'm sure that any future investigation [into the cause of the latest leak] will look at that question," he said.

The federal Pipeline and Hazardous Materials Safety Administration, in calling last month for a $423,600 fine against Chevron for the June spill, ordered the company to modify its systems so it could more swiftly detect leaks on its Salt Lake City pipeline.

"We've done that," said Mark Sullivan, Chevron's refinery manager. "We upgraded our systems and software and enhanced our training."

In the June spill, Chevron did not know about the ruptured line until the city's Fire Department called. By that time, according to federal inspectors, crude oil had been leaking for more than 10 hours.

Becker said the latest leak shows that Chevron's monitoring procedures are insufficient: "We stand by our position that the pipeline should remain closed indefinitely."