Cal. Health & Safety Code § 25299.4
(a)
(b)
(4) The regional board shall approve the variance if it finds, after investigation and public hearing, that the applicant has demonstrated by clear and convincing evidence either of the following:
(6) At least 30 days before applying to the appropriate regional board, the applicant shall notify and request the city, county, or city and county to join the applicant in the variance application before the regional board.