A sinkhole that swallowed the front end of a U.S. Postal Service truck in Washington Tuesday was likely caused by this winter’s frigid temperatures.

The ruptured water line under Parkview Court caused sediment to shift and created a “void” under the concrete, according to John Nilges, director of public services.

As the driver of the mail truck circled the cul-de-sac during a mail route, water covering the street hid the sinkhole. There were no injuries and the truck was removed from the hole with little damage.

Nilges explained the line break was the second on the water main in two days. There had been multiple breaks in the line early Monday that were repaired. 

The incident occurred about 4:30 p.m. A city crew was aware of the break and it was responding when the truck became stuck.

“He only saw the water coming out of the ground,” Nilges added. “It occurred before we could get there to secure the area.”

While repairing the break under Parkview Court, the city crew also replaced a fire hydrant to bring it up to code, he said.

“I don’t anticipate any other issues with the line,” Nilges commented.

Line Breaks

Water line breaks often occur when there is a temperature change that results in contraction and expansion of pipes. The movement disturbs sediment, sometimes resulting in sinkholes, Nilges explained.

“That is why we see them in the dead of winter and the spring,” he added.

To address the breaks, there is coordination between the water, engineering and streets departments prior to overlay projects.

When a street is targeted for resurfacing, the departments determine if there have been multiple water line breaks. 

Water mains with several breaks are repaired before the street is repaved.

“The last thing we want is a water line break right after paving a street,” Nilges said.

He submits a list of proposed street resurfacing to Washington Water/Wastewater Superintendent Kevin Quaethem, who reviews the history of breaks on a water main under the street and then a determination is made if the water main should be replaced.

City staff also examines if there is the potential for breaks due to aging water lines because the heavy equipment, particularly rollers, used on the streets during a project could rupture pipes.

“The ground vibration could potentially break a water line,” Nilges said. 

He said the policy to replace the water lines can take more time to complete the overlay.

That is what occurred during the “total reconstruction” of Oak Street between Fifth and Third streets last year. Prior to the actual resurfacing of the roadway the water lines were replaced with larger pipes, Nilges stated.

“Once we pave a street we don’t want to have to do anything to that street for another 10-15 years,” he said. “We are really trying to spend taxpayer dollars the best that we can.”

The scope of work included stormwater upgrades, and Americans With Disabilities Act (ADA) sidewalks and ramps at the intersection of Oak and Fifth streets, and Oak and Fourth streets.