I found a pdf of the 5th edition online and printed it out for the exam (~1600 pages, lol). Send me a PM if you want it and I will upload it to dropbox.
To be honest I don't recall answering any questions with it during the exam. I thought the Basic Environmental Technology by Nathanson was more useful.
Check your local library. That's where I got my copy, which was an older, single-volume edition. I checked it out in December and they let me keep renewing it until the April exam because no one else requested it.