Before We Leave

Self-explanatory. Do not build a Cleaner to clean up pollution for the entire game. If you do this, the achievement pops as the credits roll.

You can even avoid having the option to build a Cleaner by not researching it in the tech tree. It is not required in order to research any other tech as it is a dead end tech on the tree. You may inadvertently obtain it though by exploring ancient ruins as they will sometimes grant you a free tech.

Custom games allow you the option to turn off pollution. I am unsure if this will void the achievement. I had pollution set to normal spread when I got this. I have read in another guide that pollution needs to be on for this.

Regardless, the game is fairly easy, even with not being able to clean it up. Pollution creates sadness in peeps when they have to travel through it or work in it. I just made sure to cluster buildings that pollute together on the edge of an island, away from homes and food sources, when possible. This way at least half or so of the pollution is over water. Don't build dirty production buildings, like Iron and Steel Smelters, on every island. Utilize trade ships and warehouses to transport raw goods to these production sites and the finished goods to where they are needed.

You can combat sadness in peeps by providing better food than just potatoes and water. All other food sources increase happiness by different amounts. Though advanced food such as meals, smoothies, bread, and milk, all produce pollution, but in a very small radius. Other structures like the fountain, musician, and meeting square help, as well as providing better clothing, which you need to do as soon as possible anyway.

Plus I never went above the 60 peep threshold for peep expectations where they have greater demands to remain happy. Though this slider can be adjusted when you create a new game under the difficulty settings to raise the population cap at which they start to demand more. Changing difficulty presets doesn't seem to affect achievements popping, other than possibly the one for pollution as I previously mentioned. I played on default settings so I can't be 100% certain, but I have read others comment on changing presets and still popping achievements.