California Code, Health and Safety Code - HSC § 25395.97

(a) Except as provided in Section 25395.99, the agency shall issue a certificate of completion upon determining that all response actions have been satisfactorily completed in accordance with an approved response plan.

(b) Notwithstanding subdivision (a), the agency shall issue a certificate of completion when a response action plan includes long-term obligations that have not been completed, including operation and maintenance requirements or monitoring, only if the agency makes all of the following determinations:

(c) If the agency determines that long-term operation and maintenance is required at a site, the agency may, as a condition of issuing a certificate of completion, enter into an operation and maintenance agreement with the person that governs the long-term operation and maintenance activities and that provides for adequate financial assurance.