This achievement is tricky, frustrating and glitchy sometimes. I will try to save some of that post-frustration raging.
Apparently, kills are being registered randomly so you need to know a few things before starting the game :
- Put the sensitivity to the maximum, it helps tremendously!
- Fire away at your pleasure since you have unlimited ammo and don't need to reload your shotgun!
- Prepare to restart the game a few times ( took me 4 tries ) and to watch a lengthy opening cutscene. Some of the kills in a random way will be saved.
- You either need to kill 10 workers in the tunnel or to kill everyone of them at least once, can be random as well, so don't panic if you don't get it on your first or second try.
- Once the driving sequence is finished and the achievement didn't pop, just restart the game and repeat again, eventually you'll get it.
The video is mine.