This agreement and covenant not to sue is entered into by EPA, State of Colorado, and Union Pacific. Union Pacific proposes to realign certain track north of its North Yard in Denver, CO to alleviate rail traffic congestion, reduce locomotive idling time and associated air emissions, reduce the number of trains that are required to enter and exit the North Yard and to provide for a more efficient east-west main line operation through north Denver. The proposed track realignment will traverse 4 superfund sites: Broderick Wood Products, the Woodbury Chemical Site, the Sand Creek Industrial Site and the Chemical Sales Company site. Union Pacific will not acquire the entirety of any one of the Sites.