If a company acquires a site and, subsequent to their acquisition:
•existing contamination is spread by movement in the groundwater, or
•a change in the law, or of recommended accepted levels of contamination, means that the site is deemed to be contaminated; or
•previously unsuspected contamination is identified on the site
then they are not automatically treated as the polluter. The contamination was already present when they acquired the site. But you have to consider whether they have caused additional contamination or, knowing that the pollution was present, have failed to take sufficient steps to contain the pollution.