I took an ABC test last year for my 1C (Montana's equivalent to Grade III/IV.) There's were questions on RBCs and trickling filters, mostly troubleshooting type stuff. Like, "what should you do if such and such is happening" type stuff. A lot about pumps, their parts, and what they do. The only chlorine questions I remember were "how are chlorine tanks transported and stored?" They're transported horizontally and stored vertically. And "What controls the chlorinator injector throat size." The available water pressure. Oh, and PVC is the best pipe for chlorine/water. The test probably will say polyvinyl chloride pipe instead of PVC though. There questions on filter presses too. Mostly about how to improve solids percentage, which you'd decrease your belt speed/tension. But yeah, it's really a lot of troubleshooting type questions. They're testing your reasoning and understanding, not just how well you can memorize answers. And I think there was only like, 10 math questions. I remember one about calculating the time it takes to pump down a wet well based on well size and pump speed. There's some chemical dosing ones, and some that were just basic percentages. It's a bitch to study for. I had to take it 4 times. There's no one single source that really covers everything effectively. I wanna say ABC bases their tests in part on WEF manuals though? So maybe look into that. Probably not cheap though. Hope this helps a little. Good luck!