No person shall engage in the business of collecting, transporting, processing or disposing of solid waste from residential premises for the City without first entering into a contract with the City. This section does not prohibit an owner from transporting solid waste accumulating upon premises owned, occupied or used by such owner, provided such refuse is disposed of properly in an approved sanitary disposal project. Furthermore, a contract is not required for the removal, hauling, or disposal of earth and rock material from grading or excavation activities, provided that all such materials are conveyed in tight vehicles, trucks or receptacles so constructed and maintained that none of the material being transported is spilled upon any public right-of-way.