That being said—there's always a caveat—if the decision is that “we don't need to clean it up; we're just going to put a fence around it and put a security guard there; it's not that contaminated”—I'm making up an example here—that is an operational cost, not really a liability. If, however, it's actually a cleanup that is involved, we are estimating what it's going to cost to clean it up. If it's 100 years of work, we will take the 100-year projection of expenses, discount them back to present value, and that's what we book.
On May 19th, 2016. See this statement in context.