An anhydrous ammonia leak in Nevada Tuesday caused the evacuation of a 2-square-mile area in the southeast corner of the town.

Nevada officials were alerted to the leak at about 8:12 a.m. in a 30,000-gallon storage tank at the Heartland Coop, 732 W. Maple Ave., said Lt. Gary Foster of the Story County Sheriff’s Office.

“An employee of the Heartland Coop was working on a flange near a pump attached to the tank,” said Mark See, Nevada Chief of Police. “As he was loosening some bolts, the seal ruptured, causing a leak.”

In addition to the evacuated area, Nevada police alerted the residents of a nearby mobile home park.

“They were given the option to stay or leave; it was a voluntary evacuation,” Foster said. “As long as the wind was coming from the north and blowing to the south, it wasn’t causing a problem [for the mobile home residents].”

During the course of the leak, Foster said officials remained in contact with the National Weather Service, listening for wind shifts.

The leak continued until about 1 p.m., when the Des Moines Hazardous Materials team located an emergency valve to shut off the leak.

Two members of the Des Moines Haz-Mat team, Russell Gillum and Dan Lamb, were transported to Mary Greeley Medical Center, 111 Duff Ave., after receiving minor burns on their hands.

“One … remained on duty, the other went home,” said Jim Mason, Des Moines Haz-Mat coordinator. “Both are all right.”

See said he was greeted by a large gas cloud when he arrived at the scene.

“There was a large white anhydrous plume cloud drifting south from the Heartland Coop facility on Maple Street at the Union Pacific Railroad tracks,” he said. “The cloud continued emitting itself from the tank.”

Foster also saw the cloud when he arrived at the scene.

“It was quite a thick substance; it looked like smoke at the origin,” he said. “The plume rose 20 to 30 feet in the air and went approximately a distance equivalent to a city block.”

Before the leak occurred, the tank was 70 to 75 percent full, See said. After the leak, 20 to 25 percent of the anhydrous ammonia remained inside the tank.

The anhydrous ammonia at Heartland Coop is purchased by farmers and used as a crop fertilizer.

The Nevada Fire Department, the Ames Fire Department and Nevada EMS officials also assisted at the scene.