In order that the obsolete system may be removed and a modern system installed in its place and maintained immediately after the action of the board pursuant to Section 19170, the governing body may authorize the immediate removal of the obsolete system in the said zone and the installation of the modern system in said zone, and may contract to pay any costs or charges incurred by reason of such removal and such installation in equal periodic payments over a period of not to exceed the period of duration of said zone specified in the resolution establishing it.