The building, the new Williston Public Works Salt Shed, was under construction at the end of Avenue A near Pike Asphalt Plant. This is the first building to go up and the main facility has not been started yet.
Four people were sent to Fletcher Allen Health Care with non-life threatening injuries.
FOX 44 and ABC 22 photographer Steve Longchamp says it appears crews were working on the roof when it came down.
Groundbreaking for the building began about three weeks ago.
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