An ammonia leak Wednesday morning sent students in a town in far southern Dakota County to a hospital and prompted authorities to urge others to head to a nearby evacuation center. The leak of anhydrous ammonia occurred in Randolph at the River Country Co-op, which supplies farmers with Cenex products, City Clerk Sheila Ekstrom said. Along with emptying Randolph's public school, which serves grades kindergarten through 12, everyone else in Randolph is being asked to head to St. Mark's Church until the all-clear is given, she said. The leak came at about 8 a.m. when a semitrailer truck's off-loading device ruptured, said Dakota County Chief Sheriff's Deputy Tim Leslie. That sent an ammonia cloud into the air and toward the center of town, said Leslie, who added that the leak was quickly contained. About 15 students outside of Randolph School started coughing and showing other modest symptoms that required medical attention, he said. No one was seriously harmed, the chief deputy added.