The U.S. Army Environmental Command this month is scheduled to begin excavating as much as 300 tons of contaminated soil at the Tarheel Army Missile Plant in Burlington, city officials announced this week. This is the first step in a renewed effort to cleanup extensive contamination at the abandoned 22-acre site at 204 N. Graham-Hopedale Road. The site is known locally as the Western Electric plant because it had a military contract to build Nike missile guidance systems there during the Cold War.