The board shall levy an assessment pursuant to this chapter if, within six months after the completion of the hearings there is filed with the board, written consent to the contemplated project, signed and acknowledged by the following:
(a) Owners of land representing 66 per cent or more of the value of the land excluding improvements within the district, as described in the preliminary report of the appraisers, or as modified thereafter, as such value is shown by the last preceding county tax assessment roll of the county in which the land is situated.
(b) Sixty-six per cent or more of the owners of land within the district as described in the preliminary report, or as modified thereafter.