California Code, Health and Safety Code - HSC § 79820

(a) Notwithstanding any other provision of this part, if an environmental assessment of property discovers no evidence of the presence or likely presence of a release or a threat of a release of a hazardous substance, and a hazardous substance release is subsequently discovered on, to, or from that property, the owner of that property is entitled to a rebuttable presumption, affecting the burden of producing evidence, that the owner is not a liable person or responsible party for purposes of this part. An owner is entitled to this presumption whether the action is brought by the state or by a private party seeking contribution or indemnification.

(b) In an action brought against an owner of property to recover costs or expenditures incurred from the state account pursuant to this part in response to a hazardous substance release, the presumption may be rebutted if it is established by a preponderance of the evidence that the facts upon which the department made the certification pursuant to subdivision (a), (b), (c), or (d) of Section 79825 are true.