California Code, Health and Safety Code - HSC § 25395.105

(a) Notwithstanding subdivision (b) of Section 25395.102, on and after the date when the immunity specified in Section 25395.104 attaches, a person shall remain eligible for immunity if a release of hazardous materials at the site during a response action is de minimis and the agency determines that all necessary response actions to address the release have been taken.

(b) Notwithstanding subdivision (b) of Section 25395.102 with respect to a release of hazardous materials at the site that is not characterized in or through the site investigation or the response plan, a person shall remain eligible for the immunity provided in Section 25395.104, if the person takes response actions with respect to the release of hazardous materials that the agency determines to be necessary to prevent unreasonable risk to the human health and safety of the intended site occupants specified in the agreement entered into pursuant to this article.

(c) Notwithstanding subdivision (b) of Section 25395.102, on and after the date when the immunity specified in Section 25395.104 attaches, a person shall remain eligible for immunity obtained pursuant to this article with regard to a release that is the subject of a certificate of completion and immunities issued pursuant to Section 25395.104. If the person causes or contributes to a release of a hazardous material, other than a de minimis release, the person shall be responsible for responding to that release in accordance with all applicable law.