Re: It was what it was
Stanford didn't buy it. They owned the land and leased it to HP, and expected it back in reusable condition. It was uncontaminated and useful building land when they lent it, and contaminated when they got it back.
Since the lease was so long, there was a long delay between HP contaminating it and Stanford discovering that, and HP have split up in the meantime. So the right thing to do is to sue all the major bits of HP and let them argue in court about which bit is liable.
I wouldn't be at all surprised if the question of "which bit of HP" was settled by all the bits of HP agreeing either to pick one or to share the cost among them. That way, for the rest of the court case all the remaining bits of HP can present a unified front against Stanford.