“Passive migration” means the leaking, leaching or movement of a hazardous material into or through the environment, for which no human activity by the bona fide purchaser, innocent landowner, or contiguous property owner preceded the initial entry of that substance into the environment.
Source:
Section 25395.77, https://leginfo.legislature.ca.gov/faces/codes_displaySection.xhtml?lawCode=HSC§ionNum=25395.77..