Posted at: 11/19/2009 3:12 PM | KSAX.com
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Part of SD Town Evacuated After Chemical Leak

BIG STONE CITY, S.D. (AP) - Residents of this northeastern South Dakota town who were evacuated after an anhydrous ammonia leak returned to their homes Thursday morning unharmed.

Grant County Sheriff Mike McKernan said the residents returned around 5 a.m. after authorities finished cleaning the wreckage from a traffic accident on U.S. Highway 12 near the South Dakota-Minnesota state line that led to the leak. The highway also was reopened to traffic Thursday morning.

McKernan said a Cenex Harvest States semitrailer hauling about 40,000 pounds of anhydrous ammonia from Canby, Minn., to Wilmot had just crossed into South Dakota around 8 p.m. Wednesday when it collided with a van that had crossed the center line. The semi ended up on its side.

"We knew we had a small leak," the sheriff said. "We didn't know if it was going to get bigger or not, and thankfully it didn't."

McKernan estimated that between 500 and 1,000 pounds of chemical leaked, creating only a small cloud.

Anhydrous ammonia is a toxic farm fertilizer that can cause health problems in people who breathe it. In January 2002, a train derailment on the west edge of Minot, N.D., sent a cloud of anhydrous ammonia over that city. One man died trying to escape the fumes and hundreds sought treatment for eye and lung problems.

McKernan said the evacuations on the eastern edge of Big Stone City were precautionary. "We evacuated downwind, following guidelines," he said.

Between 50 and 75 people in the town of about 600 spent the night with relatives or friends or in motel rooms after leaving a temporary shelter set up at a school.

The drivers of the semi and the van were treated for minor injuries at the hospital in Ortonville, Minn. They were not immediately identified.

McKernan said the Highway Patrol was investigating why the van veered into the wrong lane. No citations were immediately issued.

(Copyright 2009 by The Associated Press. All Rights Reserved.)