I can start, and maybe the comptroller general would want to expand.
Just to be clear, the sites that are listed here are sites where the federal government has accepted sole responsibility, so the timing of a cleanup and the procedures used to clean up will vary from site to site. I think the comptroller general might be able to provide you with some details, but there are over 6,000 sites in there, so I would imagine it would be something on which they'd have to get back to you.