The immunity provided for by Section 25403.2 is only conferred if both of the following apply:

1. (a) The action is in accordance with a cleanup plan prepared by a qualified independent contractor and approved by the department, a regional board, or the designated agency, as appropriate, pursuant to Section 25403.1.
2. (b) The cleanup is found to have been undertaken and properly completed, as specified in subdivision (b) of Section 25403.2.