DOON, Iowa -- The BNSF Railway train that spilled 160,000 gallons of crude oil into floodwaters in rural Lyon County was going just below the speed limit when it derailed in June, the National Transportation Safety Board found in a preliminary report of the accident issued Thursday.
Maximum authorized speed on that section of tracks was 49 miles per hour, 1 mph above the speed NTSB investigators estimated the train was traveling when the emergency brakes were applied at around 4:35 a.m. on June 22. Of the 33 tank cars that left the tracks, 10 were breached. The damaged cars sustained tears, punctures or damaged valves, with some of the punctures as large as 3 feet by 3 feet.
The area had received between 5 and 7 inches of rain in the 48 hours before the accident, washing out track and flooding a tributary of the Little Rock River and farm fields adjacent to the derailment site. Most of the leaking crude that spilled was contained to a small triangular area between the tracks and two roads, Garfield Avenue and 270th Street, about a 1 mile south of the small Lyon County town of Doon. But some oil reached the Rock River and promoted the evacuation of 18 to 20 people, the report said.
In the aftermath of the accident, officials from BNSF, the U.S. Environmental Protection Agency, Iowa Department of Natural Resources and Lyon County, worked together to mitigate and recover the crude oil. Crews also have been replacing topsoil contaminated by the spill.
Remaining crude also has been removed from the damaged tankers, which were stacked in a nearby field. A berm was built around the cars to keep any additional leaking oil from entering the flood plain.
NTSB investigators completed on-scene work in Lyon County on July 10. Additional investigation to examine parts removed from one of the tank cars is planned at the agency's laboratories in Washington D.C.
The 110-unit train was moving nearly 2.5 million gallons of crude from a terminal in Alberta, Canada to Houston, Texas for ConocoPhillips, according to the report. Each car carried about 29,000 gallons. The shipper classified the mixture of heavy crude and diluent mixture as "Hazard Class 3, Packing Group 1 (highest degree of danger.)
The derailed tankers were older cars that were upgraded to DOT-117R safety standards. Federal regulations require such tankers to be retrofitted or removed from service by 2020.
After the derailment near Doon, BNSF warned shippers of plans to ban retrofitted cars in all new contracts, the news service Reuters reported, citing sources familiar with the discussion.
Editor's note: An earlier version of this story mischaracterized the estimated speed of the train in relationship to the speed limit for that section of track.