All work within the limits of any public area shall be prosecuted to completion with due diligence. If any excavation is left open beyond a time reasonably necessary to fill the same, the City Engineer may cause the same to be backfilled and the public area restored forthwith. Any cost incurred in such work shall be charged to the side sewer contractor in charge of the work and shall be immediately payable to the Treasurer by the contractor upon written notification of the amount thereof given to the contractor or posted at the location. (Ord. 208 § 17, 1957).