I'm not sure I follow the above logic. Landfill isn't on the Exam outline, but study it anyways because it is in the CERM?
I do agree that anything not on the exam outline could still show up on the exam to make for a difficult question (what are you going to do about it - ha ha?) Tailing pond waste for example. But tailing pond waste isn't on the outline, it also happens to not be in the CERM. Going by that logic, if I'm studying landfill shouldn't I also read up on tailing ponds, and a hundred other subjects while I'm at it?
Does NCEES look through the CERM to get material to make the exam? I'd guess not. The CERM is a dump of information, much of it overkill to what we need to know (going by the exam outline). Amazingly, some information is missing entirely. How about a Chapter devoted to Wastewater (collection systems) and Water Treatment (hydraulic loading & distribution systems). These are prominently on the outline for the breadth exam, and sadly each receives just a few pages in the CERM.
If there is a question on landfills, that sucks. But hopefully you have the time and resources to look up those few 'Off-The-Exam-Outline' questions. I just wouldn't waste time studying them because time is limited and could be better put into being more prepared for things that are on the outline.
In order of figuring out what is important to study, I'm going by
1. NCEES exam outline
2-999. NCEES practice exams
1000. CERM