This post has been updated:

State leaders reacted with grave concern Wednesday after Union Pacific announced plans to resume transporting crude oil through the Columbia River Gorge despite calls for a pause on oil trains in Oregon.

The railroad temporarily stopped sending oil trains through the Gorge after 16 cars on a 96-car train derailed in Mosier on June 3. Four cars caught fire and leaked 42,000 gallons of oil in a crash that forced hundreds of people to evacuate and closed Interstate 84.

Wes Lujan, Union Pacific's vice president of public affairs, said in an email to officials that normal operations would "resume over the course of this week. This includes transporting crude oil." He cited a federal provision that "requires railroads to transport crude oil and other hazardous materials."

"If a customer delivers a crude oil tank car in conformity with U.S. Department of Transportation requirements," he wrote, "we are obligated to transport the rail car to its destination."

But Gov. Kate Brown, along with members of the state's congressional delegation, said Union Pacific's decision to restart oil trains so soon after the derailment will put people at risk.

"As I said last week and again as oil begins to roll through our Gorge, I call on federal authorities to ban the transport of oil by rail until safety can be greatly improved and our first responders have the tools they need," Brown said in a statement.

Last week, Oregon transportation officials asked for an indefinite moratorium on oil trains moving through the state after preliminary findings from the June 3 derailment showed inspectors might not be able to prevent a problem with track bolts that likely led to the crash.

In a June 8 letter to the Federal Railroad Administration, an Oregon Department of Transportation official said recent inspections failed to find broken screws along the track in Mosier.

"Until the underlying cause of the bolt failures is understood and a means of detecting this defect is developed," wrote Hal Gard, the state's rail and public transit administrator, "we request a moratorium on running unit trains over sections of track that contain track fasteners of this material in the state of Oregon."

U.S. Sens. Ron Wyden and Jeff Merkley joined Brown in criticizing Union Pacific's decision Wednesday.

In a joint letter to the Federal Railroad Administration, they asked for a ban on oil trains through the Gorge until the federal agency has assembled a final investigative report on the Mosier derailment and has "ensured all steps have been taken to prevent similar accidents."

If oil trains do resume through the Gorge, the senators wrote, then speed limits should be put in place.

The Federal Railroad Administration has been in "close and regular contact" with state leaders, an agency spokesman said, and their investigation is ongoing.

"If FRA finds that railroads need to make operational changes, we will direct them to do so," spokesman Marc Willis said in a statement.

As The Oregonian/OregonLive has reported, oil traffic in Oregon peaked in 2014, when 24,199 tank cars moved through the state. The state saw a 60 percent decrease last year after oil prices fell. As of last November, Union Pacific was running three oil trains a month past Mosier.

But that could change. Plans for an oil train terminal Vancouver, Washington -- billed as the nation's largest at 360,000 barrels a day -- would bring an additional four trains daily through the Gorge.

Those trains would pass many small towns, like Mosier, poorly equipped to deal with fiery derailments. In Mosier, Wyden and Merkley noted in their letter, the water needed to fight the fire depleted the city's main well.

The senators also emphasized that trains moving through Gorge require additional safety measures given the region's "unique environmental, economic, cultural and tribal importance."

The Gorge is a designated National Scenic Area, and the site of a slew of outdoor tourism activities, while the Columbia River is home to endangered species and encompasses the Columbia River Treaty Tribes' fishing ground.

Justin Jacobs, a Union Pacific spokesman, said the railroad will inspect tracks more frequently in the wake of the Mosier derailment. Workers will carry out monthly "walking inspections" of areas in the Gorge similar to where the derailment took place.

And inspections in which track workers drive specially outfitted trucks on the rails will now happen three times a week instead of two.

Jacobs said inspectors will also step up inspections for bolt failures, using a special machine that replicates the pressure a locomotive applies to tracks four times a year instead of once every 18 months.

"If we didn't think it was safe to do this, we wouldn't do it," he said. "At end of day, we have tens of thousands of customers that rely on us to move goods and services that people use everyday."

More than a dozen explosions have been recorded in North America since oil traffic picked up nationally in 2012.

Brett VandenHeuvel, executive director of Columbia Riverkeeper, called oil trains "an experiment the railroads tried, and it failed."

"Starting oil trains up again is reckless," he said. "I'm deeply disappointed Union Pacific is putting our safety at risk here in the Gorge, in Portland and all along the rail lines."

- Talia Richman

trichman@oregonian.com

@TaliRichman