The Chairperson of the City Planning Commission may modify the general requirements of the publicly accessible open spaces listed in Section 93-75 (Publicly Accessible Open Spaces in Subdistrict F), and private streets and pedestrian ways listed in Section 93-76 (Publicly Accessible Private Streets and Pedestrian Ways in Subdistrict F), provided that the Chairperson certifies to the Commissioner of Buildings that such a change is necessary to accommodate unforeseen ventilation demands within the Western Rail Yard. In addition to the site and landscape plans required pursuant to Section 93-78, a mechanical plan shall be provided demonstrating the need to modify such general requirements.