California Code, Streets and Highways Code - SHC § 19176

The board of supervisors shall, in the first fiscal year in which a special tax or assessment, as the case may be, may be levied in and on behalf of the zone, levy a special tax or assessment upon the taxable property therein for the purposes ofthe zone, and shall include inthe levy a sum sufficient to repay to the county the amounts transferred to the district pursuant to Section 19175. The amounts so transferred shall be retransferred to the county treasury from the first available receipts fromthe special levy inthe zone.

Thereafter, in the succeeding fiscal year or years during whichthe temporary zone remains in existence, the board of supervisors shall levy a special tax or assessment therein sufficient to pay any additional costs or charges incurred by reason of the removal of the obsolete system and the installation ofthe modern system therein, which may by contract be made payable in such year or years.

All special taxes or assessments levied in and on behalf of a zone, pursuant to this section, are in addition to any taxes or assessments levied therein for and on behalf of the district as a whole.