A qualified senior citizen who elects to have a special assessment deferred pursuant to the provisions of this chapter shall enter into a contract to be prepared by the City Attorney. The 10% interest rate chargeable for docketed assessment liens according to the provisions of §§ 11 and 12 of Ord. 393 as amended by Ord. 598 enacted January 5, 1976, shall not apply to a special assessment deferred for a senior citizen who has entered into an assessment deferral agreement with the city.