California Code, Government Code - GOV § 8670.27

(b) If a responsible party or potentially responsible party reasonably, and in good faith, believes that the directions or orders given by the administrator pursuant to subdivision (a) will substantially endanger the public safety or the environment, the party may refuse to act in compliance with the orders or directions of the administrator. The responsible party or potentially responsible party shall state, at the time of the refusal, the reasons why the party refuses to follow the orders or directions of the administrator. The responsible party or potentially responsible party shall give the administrator written notice of the reasons for the refusal within 48 hours of refusing to follow the orders or directions of the administrator. In any civil or criminal proceeding commenced pursuant to this section, the burden of proof shall be on the responsible party or potentially responsible party to demonstrate, by clear and convincing evidence, why the refusal to follow the orders or directions of the administrator was justified under the circumstances.