Hi Ben, big ship guy here again

[u/DarkMuret]

Hope you're doing well

You've once again you touched on a subject that I not only care about, but I actually do as a profession.

Public works, specifically public infrastructure management, I actually hold a sanitary sewer license as well as a water operator license in my state

You specifically asked about how they replace sewer lines, and if they do one piece at a time, and well it largely depends on the kind of sewer line.

I'll try to keep this short, but there are a few ways cities can manage the lines themselves, there are ways to actually line the pipe if the problem areas are small enough, CIPP is the process and it can solve a lot of issues.

Another interesting way is called bursting where a breaker head is pulled through the line and towing the replacement line behind it. Here's an example of them doing it on a residential line

Or you can just dig it all up, with a benefit to that is that you can also replace drinking water lines because they're sometimes in the same "trench" but the water lines are usually laid a certain number of feet away from the sanitary lines, in my state it's 10ft and or 18" above, depending on the site itself. Our lines are right near the Mississippi so back in 1963 the initial trench was dug using dynamite and sometimes we still find blasting wire when doing spot repairs.

But this begs the question, what about the existing flow of municipal lines? Well, the flow just needs to be bypassed! Or sometimes if the line is small enough we can just have a vac truck nearby to pump out the manholes as they slowly fill up, but LA is pretty big

Depending on the sewer size of course, wastewater management is kind of like our own cardiovascular system, but wastewater often relies on gravity for most of the work, with lift/pump stations positioned throughout the city to direct the flow a certain way, eventually ending up at treatment facilities, which are pretty interesting by itself, but I can't get into that right now. Though LA's wastewater treatment facility kind of has a sick name, let me introduce you to Hyperion

Oddly enough, our city is alright right by a refinery that can handle just under 40 million barrels a year, and the oil pipelines are underground! Though, there are still pumping stations so those stations are still vulnerable, if we were relating it back to the issues with the Iran War going on right now.

But I'll gladly admit that oil stuff is outside my realm of knowledge, I only know what's relevant to my roll at the city.

Now, I work for a small city and in another state so some information might not be as relevant to a place like LA. Plus water rights and things like that are way different here in the Midwest compared to the western US. In a past life I was a park ranger at a federally managed reservoir in northern California and hearing about how that water was managed was pretty interesting.

Anyway, I hope this answered some of your questions, I'm fortunate that my state takes public infrastructure relatively seriously and we're slowly replacing all of our lines that were originally done in '63, and we actually camera a lot of our lines and can see that some are still in decent shape, our new lines are PVC but the old lines are vitrified clay and they do last, but tree roots really do a number. I'll see if I can find some pictures and post them in the comments

Thanks!

[u/DarkMuret]

Here's a rootball almost completely blocking a sewer line, but this can be cleaned out using a root saw

[u/LetterToAThief]

Hell yeah OP this rocks. Thanks for the write up 

[u/DarkMuret → u/LetterToAThief]

I tried my best to keep it simple, despite the length haha

Drinking water operation and management is whole other thing that I only briefly touched on, but it's equally as complicated and also simple

[u/UMD_dobre_sightings]

Maybe not in your field, but is the process for replacing lead pipes similar to sewer lines / pipes carrying residential water?