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Comment by schrectacular | Hacker News Reader

The thought occurred to me some 25+ years ago that today's landfills will be tomorrow's mines. I hope it isn't true but taking the very long view I'm afraid it will be.

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A british inventor created a setup with two long vibrating plates with ferrofluid in between. A flaky powder made from garbage was dumped in on one side and came out the other end beautifully separated in many layers by density. (with one mixed layers in between that went back in at the beginning) Innitially he "knew" it was silly to use something as expensive as ferrofluid but planned to try other substances if it worked. It turned out the process produced a lot more ferrofluid than it used.

No one was interested in further research.

edit: I see some research is now happening.

We already mine landfills -- mostly for land reclamation but sometimes to recover resources.

In the longer run, when there's been more compaction, settling, and densification (and changes in what things are valuable), and more need to reclaim land that was previously landfilled, we will do this more.

People sometimes build stuff on top of landfills.

Like ski courses!

Indeed, sometimes big things. The landfill we used when I was growing up is now beneath a Home Depot, which was built over the top of it almost 25 years ago. The landfill in this case was unlined, too.

Yup. It is a little undesirable for various reasons, and not every landfill is suitable for construction on top (seismics, sealing/capping technique, materials, etc).

Example: Shoreline Amphitheater, near Google HQ in Mountain View. Built on top of a landfill. For a while in the 80s, there were occasionally small fires during shows when people lit cigarettes. Google also harvested the methane and used it to power some stuff, although I can't find an authoritative article with details.

Several schools I know of have part of their playing fields on reclaimed land that's former landfill. You can't build on it because you have no idea what sort of gases and possibly toxins will work their way up from below, but wide open fields with free air movement that aren't round-the-clock occupied are fine. The only downside is that for an initial period you need to re-cap places with soil every few years as the fill underneath settles. There was one place where they'd paved over it rather than leaving it as soil to create tennis courts and after a few years it was a sort of dune landscape since they couldn't backfill the dips with soil. It was quite picturesque actually, a sort of post-apocalyptic look with miniature ponds with reeds growing in them and occasional visits from ducks. Sure, they'd lose a kid in one from time to time, but being a large school they didn't have a shortage of those.

This shopping center was built on a landfill

https://www.wskg.org/regional-news/2025-08-08/binghamton-off...

when I first saw it in the 1990s it was kinda on the outs, like K-Mart was already failing (as a business) and the parking lot was visibly wavy because of subsidence. Funny the New York Pizzeria mentioned in that article is run by my relatives.

Today’s landfills are already used for natural gas generation.

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