The subdivider shall be responsible for the cost of installing the natural gas system within all new subdivisions. The necessary piping and appurtenances shall be installed by the City and the costs of all materials, equipment, and labor shall be billed to and paid by the subdivider. Within ninety (90) days of meter installation or upon permanent occupancy of the principal building on a lot in the new subdivision, a refund shall be made to the subdivider, of the costs of materials and installation of the gas main, prorated as to the ratio of said lot to the total number of said building lots in the subdivision.