At a Tuesday evening Marathon County board meeting, officials said a rooftop ammonia pipe at Abbyland in Abbotsford sustained a two-foot stress fracture, which released liquid and vapor ammonia.
The liquid ammonia flowed into a storm drain while light winds moved the leaking vapor through the air.
Eighteen people were hospitalized, and nearby residents were evacuated from the leak.
Around 200 residents were alerted of the evacuation via a mass notification system called Everbridge. A fraction of those residents responded to the message.
The fractured ammonia line was shut off around 8:25 PM. Emergency crews were on scene for several hours after that.
Emergency management officials said the situation was handled well, but communication between departments can improve.
"Whether it's an exercise or an actual incident, communications are always a challenge," said Phil Rentmeester, Emergency Management Director for Marathon County. "Especially when you're dealing with a situation like this across two different counties and all the multiple agencies that were involved."
Rentmeester advises Marathon County residents to sign up for the Everbridge system.