California Code, Health and Safety Code - HSC § 106780

(a) Except as provided in Section 106790, no person may provide radon services for the general public, or represent or advertise that he or she may provide radon services unless that person meets both of the following requirements:

(b) Persons certified to provide radon services shall successfully complete and submit to the department proof of completion of the National Radon Measurement Proficiency Program of the National Environmental Health Association or the National Radon Safety Board Certified Radon Professional Program every two years after initial certification.

(c) A copy of the current certificate of completion shall be submitted to the department at least 14 days prior to conducting radon services within the state.