The longtime head of Atlanta’s Office of Contract Compliance announced Monday his decision to retire, effective immediately. Mayor Kasim Reed spokeswoman Anne Torres did not explain why Hubert Owens, a 20-year-veteran of the city, retired on a Monday without advance notice. Owens, who according to the city has served as the director of the compliance office since 2002, is also a prominent college football referee. He could not be quickly reached for comment.