CUSTER, Wash. — Derailed train cars are set to be removed in Custer this week.

Officials with the Washington Department of Ecology say they plan to start removing the train cars starting Monday after a tanker train hauling crude oil derailed on December 22.

A spokesperson for BNSF Railways said three cars ruptured, spilling an unknown amount of crude oil onto the ground.

The cause of the derailment is still unknown.

Crews worked through the weekend to remove the remaining oil from the train cars and will transport it to a refinery in Ferndale.