No permit required under this division shall be issued unless and until the applicant for the permit has deposited with the city engineer a cash deposit in a sum as set from time to time by order of the board of commissioners, to ensure the proper restoration of the ground and laying of the pavement. Where the amount of the deposit is clearly inadequate to cover the cost of relaying the surface of the ground or pavement, the city engineer may increase the amount of the deposit to an amount considered by him to be adequate to cover the cost. From this deposit shall be deducted the expense to the city of relaying the surface of the ground or pavement and of making the refill if this is done by the city or at its expense the balance shall be returned to the applicant without interest after the tunnel or excavation is completely refilled and the surface or pavement is restored.
(Code 1977, § 11.510(4))