Juan Bucio, 46, a father of two sons, became separated from his dive partner in the water Monday night while trying to rescue a man who had fallen off a boat into the river near Ashland Avenue, fire officials said. Bucio, a 15-year veteran who served on the Fire Department’s dive team for more than a decade, disappeared briefly in the water, was located and then was lifted onto the riverbank. He was taken to Stroger Hospital, where he was pronounced dead about two hours after firefighters received the rescue call.