California Code, Public Utilities Code - PUC § 15736

At the hearing or at any time prior thereto, any owner of taxable property within the proposed district may file a petition with the board of supervisors asking that the property described in the petition be excluded from the proposed district.  If the board, after hearing, finds the described property will not be substantially benefited by its inclusion in the district, it may exclude such property.  At the hearing the board shall make such changes in the proposed boundaries as it deems advisable and shall define and establish the boundaries.