Dealing with Garbage and Sewage (the dirty stuff) in Cities: Skylines can be a huge problem, but I have some advice for you on both of these topics that should help you clean up your cities and keep from having to figure the issue out. These two issues catch a lot of players by the ankles because it's hard to position sewage and garbage without it impacting your own, but you need it so much and unlike fire, police, and health there is no way to put it in with your communities. They're outcasts who have to sit on the edge.
Here are some tips on dealing with garbage and sewage in Cities: Skyline.
For garbage, you only have two units that can accept garbage: the landfill and the incinerator. These two units are the only ones that will remove garbage. This is how they operate. They send out garbage trucks who visits industry, residential, and commercial with no bias. These trucks pick up trash then return to offload it at the landfill or incinerator, where it turns into pollution (and/or power).
Each landfill and incinerator can only hold so much, but both have rather long range. The challenge is making sure the trucks can reach every part of your city, but the pollution stays away from everything but industry (which still honestly doesn't enjoy it).
To solve this issue, you're going to want to be okay with putting breathing areas between your cities. Now, when I do specifically, is make islands on my maps where the landfills and incinerators go. It's a nice visual seperator, but the goal is really to just keep them away from your cities. It's beneficial for traffic as well to keep things separate a good bit and have lots of breathing room between your districts.
Remember that they do have very long distances and will travel on the interstate, so it won't affect highway traffic to make an off ramp for garbage areas.
This one is a cool one - there is three ways to deal with sewage. The first is the natural way, make sure it pumps out downstream until you get the water treatment plant, at which point you can clean water a lot better. The second way is to pump it into standing water, the pollution will continue to fill the Lake forever. While I've NEVER seen it overfill a lake with sewage, you can install a pump that's NOT connected to anything at all, just one cell of pipe from it, to pump water out of an area.
The last way is to get a map with the glitch that forces the water to go into a void. These sewage dumps are very visually attractive as the sewage is hidden and you don't have large streaks of pollution in your town. However, to make best use of them, you'll need to download a map off of the Steam workshop that has this feature or do it yourself.
I haven't discovered it outside of maps like "OCD" but I assume it's some hightmap glitch. Anyway look for it in the Steam Workshop.
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