The man was working with a compressed air tool in a ditch when the accident happened at 1:50 p.m., Sgt. Josh McClure said.
The crews were part of the hospital expansion project.
The accident knocked out power to about 900 people for about 35 minutes, according to the Snohomish County Public Utility District.
Officials initially said the accident involved a backhoe. The state Department of Labor and Industries also is investigating.
No additional details were released Wednesday.
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