TEUTOPOLIS, Ill. (WTVO) — Around 500 residents were authorized to return back to their Teutopolis homes on Saturday night after 4,000 gallons of anhydrous ammonia spilled from a crashed semi-truck in an accident that killed five, Illinois State Police announced.

The truck, which was carrying approximately 7,500 gallons of the toxic liquid at the time of the accident, was involved in a multi-vehicle crash on U.S. 40 on Friday night. The chemical leak produced a large plume of gas, prompting an evacuation of nearby residents.

Police were notified of the accident at approximately 9:25 p.m. U.S. 40 was closed between Effingham and Montrose while the accident and spill were addressed.

According to state police, a private hazmat company removed the ammonia from the truck while the U.S. Environmental Protection Agency performed air monitoring throughout the community. The area was declared safe for residents to return before 8 p.m. Saturday.

The Illinois Department of Public Health will continue to monitor the area.

“We remind residents to ventilate their homes upon return. If they detect unusual odors, they should leave immediately and call 911,” said IDPH Director Dr. Sameer Vohra in a Sunday media release.

“IDPH is also working on guidance regarding testing of private water wells in the immediate vicinity of the incident to check for possible contamination.  We remain in consultation with the local health department and the Illinois Department of Agriculture regarding animals and livestock in the area and procedures for transporting them for veterinary evaluation.”  

The cause of the crash is still under investigation, according to police.