Treatment Plant Manager's Diary is a file that can be found in Resident Evil Zero. While the lack of year-dating leaves its timeframe ambiguous, the History of Biohazard timeline which was used to advertise Resident Evil: The Umbrella Chronicles confirmed that it is set in 1998.
The file can be found at the Power supply and air conditioning room on Treatment Plant B7.
Damn it! Why is normal industrial waste being delivered here? This is an Umbrella Corporation facility. We can't deal with this volume of material. Plus they're sending us contaminated materials that we can't process. What are we supposed to do with it?
Well, looks like they're closing it down. Not surprising, using it like they did. Had to be done, but... It was pretty sudden. It's not like they cared until now. Anyway, as long as I get out of here, I don't care what they do.