The broken fasteners officials believe led part of a 96-car oil train to derail and explode in the Columbia River Gorge on June 3 weren't even detectable by regular safety monitoring, a finding that's prompting the state to call for a pause on oil train transport in the gorge and elsewhere.

According to Oregon Department of Transportation Rail and Public Transit Administrator Hal Gard, an inspection of the offending tracks had been carried out just days before, on May 31, and turned up nothing.

"Given the nature of this defect, it was not detectable by normal inspection methods," Gard wrote in a June 8 letter to the Federal Railway Administration. The "defect" in question is an unknown number of Rectangular Head Timber Coach Screws, known as lag bolts, on the section of Union Pacific track near Mosier, OR, about 68 miles east of Portland. The bolts had been installed in 2013 at the earliest.

Gard says it's unclear how those screws broke, but that many "exhibited evidence of having been broken for a significant amount of time prior to the derailment." And in light of all the uncertainties, ODOT is joining a growing chorus of local leaders in asking the feds to stop oil trains from coming through the gorge—and anywhere else in the state with this type of track—at least for the time being.

"Until the underlying cause of the bolt failures is understood and a means of detecting this defect is developed, we request a moratorium on running unit oil trains over sections of track that contain track fasteners of this material within the state of Oregon," Gard wrote in the June 8 memo. It's unclear if the FRA responded to the request. A spokesperson hasn't answered calls for comment.

By "unit trains," Gard is referring to trains that solely carry oil. Union Pacific says it began carrying oil tankers through the gorge just two days after the derailment, but in so-called "mixed manifest' trains that pull a variety of cargo. The railroad declined on Wednesday to offer a count of how many oil cars have traveled through the gorge since the crash, or how many are going through a week, on average.

Lag bolts. Not doing what they should.
Lag bolts. Not doing what they should. ODOT

The railroad also declined to release its internal report on the causes of the crash. Spokesperson Justin Jacobs said the company had forwarded that report to the FRA, but an FRA spokesperson this morning said that wasn't the case. Union Pacific has until July 3, said the FRA spokesperson, Tiffany Lindemann.

The ODOT memo, first reported by the Portland Tribune, casts the June 3 derailment in a new light. In the wake of the crash, Union Pacific has called the problems with the fasteners rare, praised the safety of its track, and said it will test the stretch of track through Mosier every three months, versus the former 18 month intervals. But Gard's memo suggests that wouldn't much matter.

That's bolstered by a PowerPoint presentation from Gard [PDF], which shows Union Pacific inspected twice in the weeks leading up to the derailment—once with a "gage restraint measurement system" (on May 11), and on May 31 with a piece of ultrasound equipment used to ferret out "internal rail defects."

"No defects were found during these inspections," the presentation says.

Here's Gard's full memo.