Officials question oil spill estimate

BILLINGS – State environmental regulators have asked Exxon Mobil to justify its estimate for how much oil spilled into the Yellowstone River, citing the company’s changing timeline on how long it took to stop a leaking pipeline.

The Texas-based company has said between 31,500 and 42,000 gallons of crude flowed into the Yellowstone following the leak near Laurel on July 1. That oil has fouled shoreline and contaminated backwaters along dozens of miles of the scenic river.

Exxon Mobil Pipeline president Gary Pruessing initially said it took six minutes to shut down the pumps on the Silvertip pipeline. But information submitted by the company to federal pipeline safety regulators later revealed it took almost an hour to fully stop the flow.

In a letter to Exxon executives, Montana Department of Environmental Quality Director Richard Opper asked for an explanation of why the spill volume was not changed given the longer timeline.

“Since the event occurred, ExxonMobil has increased its estimate of the duration of the spill event 10-fold from its original assertion,” Opper wrote. “Despite this revision as to the duration of the event, ExxonMobil has not revised its estimate as to the volume of the spill into the river.”

Exxon Mobil representatives said last week the spill estimate was based on the correct timeline. Spokeswoman Cynthia Bergman said Tuesday the company believes its estimate is accurate.

The estimate included oil lost after the pumps were shut down but before a series of valves were closed to fully seal off the section of failed pipeline, she said.

It’s still unknown why the pipeline failed. Speculation has centered on high waters that potentially scoured out the river bed and exposed the buried pipe to damaging rocks and debris.

When water conditions allow, Exxon Mobil plans to use a side-scanning sonar to investigate the damaged section of pipeline, said Steve Merritt, the Environmental Protection Agency’s on-scene coordinator. He said one question that needs to be answered is whether any oil remains trapped in the line.

Because much of the oil was swept away by the river, only 1 to 5 percent of the total amount spilled is expected to be recovered.

As of Tuesday, 942 barrels of oily water had been collected by crews. If the water were removed, that would equal roughly 9 barrels of crude oil, or less than 400 gallons, Merritt said