The work proposed to be done under such private contract must be of a class or type approved and recommended by the City Engineer. Such work must be done under the direction and to the satisfaction of the Director of Public Works and the materials to be used therein must be in accordance with specifications adopted by the Director of Public Works for similar work, and be to the satisfaction of the Director of Public Works.
The Director of Public Works shall fix the time within which the work shall be completed which time shall begin to run from the date of the order of said Director granting the permission for the doing of the same.
When the work shall have been completed to the satisfaction of the City Engineer and the Director of Public Works, the said Director shall so declare by order, and thereupon deliver to the contractor a certificate to that effect.