Federal lawyers are prosecuting a wastewater plant operator for Union Pacific Railroad, alleging he allowed thousands of gallons of oil to seep from an overflowing tank into the Willamette River in January 2018.

Robert LaRue Webb II is accused of negligently discharging oil from a storage tank at Union Pacific’s Albina Yard in North Portland into the river, causing a visible dark film on the water, according to a court filing in U.S. District Court in Portland.

Webb faces one count of unlawful discharge of oil into the river, a violation of the Clean Water Act.

“Union Pacific has cooperated fully with the government in connection with its investigation of this incident and will continue to do so,” Tim McMahan, a Union Pacific spokesman, said Monday. McMahan said Webb worked for a contractor and was removed from the job following an investigation.

As part of his responsibilities, Webb operated an oil-water separator and then used a manually activated electric pump to transfer the oil emitted by the separator to a nearby 10,000-gallon oil tank.

About 12:20 p.m. on Jan. 23, Webb activated the pump but the tank was near capacity. Webb then walked away from the pump and left it unattended for about an hour, Assistant U.S. Attorney Ryan Bounds wrote in a criminal information filed Friday.

The tank overflowed, but the pump continued running. By the time the pump was shut off, several thousands of gallons of oil had escaped, flowed into a nearby storm drain and then directly into the Willamette River, Bounds wrote.

— Maxine Bernstein