Comment by yojo
4 days ago
Leaks are more common on the pressurized side. Which is the clean water coming in. If you have hairy fatbergs in your supply you’ve got bigger problems.
The article describes them being “dropped in at hydrants.” So I think they’re punting on the “hairier” problem of the sewer side.
Edit: okay, I kept reading and they do mention pressurized waste lines. That does seem harder, especially since you’re going to get root intrusion on old public lines.
Unpressurized sewers are often pretty leaky actually. A lot of early sewage systems have combined sanitary and storm sewers, but around the 1940s, separating santiary sewers from runoff drains became common for new systems. Even in separate systems, most sewage systems see an increase in volume during the rainy season, and it's not because people pee more when it's wet outside (maybe they do, but...). Ground water leaks into the sanitary sewers; and presumably sewage leaks out of the pipes into the ground at times. As long as the slopes are reasonable, and there is free flow, leaks aren't a big deal... but leaks and gaps do allow for root intrusion which leads to clogs. Typically municipal sewer lines are pretty deep and tend to be towards the middle of the street which makes it harder for plants to get in there, but some plants are pretty persistent.
Here's an EPA manual from 1971, Prevention and Correction of Excessive Infiltration and Inflow into Sewer Systems. The key thing here is that the goal isn't to eliminate infiltration, but to eliminate excessive infiltration; it's all tradeoffs.
https://nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=9100WH40.txt
> you have hairy fatbergs in your supply you’ve got bigger problems.
Shudder at the thought ...