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SALT LAKE CITY (AP) -- Chevron Corp. says constantly changing pressures in an oil pipeline that leaked into a Salt Lake City creek make such spills difficult to detect, raising questions about how long the leak last month went unnoticed.
The company said it's using better computer software and making other control-room changes to better detect leaks like the half-inch hole that spilled an estimated 33,000 gallons of crude oil into the city's waterways.
Chevron's latest assessment came in a written response to a series of questions posed by U.S. Rep. Jim Matheson, D-Utah. Matheson said he's waiting for federal regulators to make their own determination about the pipeline's problems.
Chevron's four-page response was obtained from Matheson's office and verified by the company. The company said detecting the leak was "challenging" because pressures inside the 182-mile pipeline are constantly changing.
Chevron's control-room operators didn't know about the leak until Salt Lake firefighters reported that crude oil was gushing down Red Butte Creek.
Matheson said he believes the pipeline had been leaking for eight hours, but the company has made no determination about how long the leak went undetected, Chevron spokesman Mickey Driver said Friday.
"We are doing our own study to determine what happened," he said.
Salt Lake City's Fire Department notified Chevron of the leak at about 6 a.m. June 12, but Mayor Ralph Becker has said residents noticed the odor of oil the previous night. The pipeline, which delivers crude oil from Rangley, Colo., to Chevron's Salt Lake City refinery, was leaking residual amounts of oil until the morning of June 13.
Chevron said the difficulties of monitoring the pipeline for leaks include radical changes in terrain -- the pipeline climbs as high as 10,000 feet in elevation along the route, then drops several thousand feet into the Salt Lake basin.
Those elevation changes, combined with crude oils that differ in density and temperature, keep pressures in a constant state of flux and can mask a minor leak.
Chevron explained these difficulties to Matheson without conceding that the leak went undetected for hours. Driver said questions about the timeline of the leak will be answered later.
Chevron still believes a freak event was behind the June 12 leak. According to the San Ramon, Calif.-based company, a short in a power line traveled through a utility fence post to burn a hole in the pipeline's casing.
(Copyright 2010 by The Associated Press. All Rights Reserved.)
