"Whatever they left there" is the most terrifying part of a lot of these long term sites. Without documentation, and as GP mentioned, you can scour the site as

"Whatever they left there" is the most terrifying part of a lot of these long term sites. Without documentation, and as GP mentioned, you can scour the site as much as you want... and easily miss a single buried barrel of god-knows-what, that only the guy who tossed it off the truck knows was there (if even they knew), until it finally rusts through or is punctured. Ironically, leaking or unsealed waste sites are probably safer, because it pervades the environment, is more easily detectable, and doesn't have sudden failure modes.