An emergency personnel employee works at the scene after a CSX freight train derailed in Washington on Sunday, May 1, 2016. (AP Photo/Cliff Owen)

A wheel problem may have caused a CSX train derailment in May that spilled chemicals along a busy rail corridor in the District, according to an incident report filed with the Federal Railroad Administration.

A CSX train carrying sodium hydroxide derailed May 1 in Northeast Washington. Fourteen of the train’s 175 cars derailed, with one car leaking more than 700 gallons of sodium hydroxide — a hazardous chemical used in cleaning agents. Another tank car leaked calcium chloride, described as “non-hazardous,” and a third leaked ethanol.

The derailment on an early Sunday morning kept some residents away from their homes for hours and forced the closure of the Rhode Island Avenue Metro station. The wreck also shut down the CSX tracks for three days, disrupting MARC and Amtrak service.

CSX Transportation said in the report to FRA that it determined the cause of the derailment was a failure in the “journal” portion of an axle on the first car that derailed, 70 cars into the train. Rob Doolittle, a spokesman for CSX, said the broken wheel is being analyzed to evaluate what may have caused the axle to break.

“CSX inspects all rail cars for mechanical fitness prior to a train being dispatched to its destination, in compliance with company policy and federal safety requirements,” he said. But he said that part of the rail car axle is not accessible for visual or machine inspection.

The derailment caused nearly $500,000 in track damage and more than $400,000 in damage to equipment, according to the report. Doolittle said the rail company covered those costs.

The report provides CSX’s assessment of the derailment, but federal investigators have yet to release an official cause. FRA spokesman Matthew Lehner said the agency continues to investigate the incident but has no update of the investigation at this time.

The train was traveling at 27 miles per hour when it derailed near a rail switch in the vicinity of Rhode Island Avenue and Ninth Street NE. The wreckage visible from the Rhode Island Avenue Metro station prompted fear of chemical exposure and sparked renewed concern about the transportation of hazardous chemicals through the District. Twenty-one cars were carrying hazardous materials, according to the report

In the hours after the 6:35 a.m. derailment, authorities said that there was no impact to air or water quality and that all of the leaks were contained. As part of the cleanup effort, the soil affected by the sodium hydroxide spill was excavated and replaced with clean fill.

In May, CSX reported that there were no fatalities or injuries, but the FRA report notes one person was injured. Doolittle said the derailment itself didn’t cause injuries, but one worker in the cleanup effort reported some skin irritation after coming into contact with the contaminated soil.

“Safety is CSX’s highest priority, and our goal is to deliver every load of freight safely to its intended destination,” he said. “Any lessons we learn from the investigation of this incident will be applied in our operations going forward, to avoid similar incidents in the future if at all possible.”