Unless risks posed by vapors from chlorinated organic contaminants (i.e., PCE) are demonstrated to be below a level of concern to the satisfaction of Region 8 EPA, for residential buildings within the area depicted in the vapor mitigation area, appropriate vapor mitigation measures will be implemented. Appropriate measures may include passive mitigation installed in connection with initial building construction or other periodic vapor monitoring and mitigation if required in the future. (Ord. 6/26/2007O-8 § 1 (Exh. A (part)))