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There was a good comment on r/oil by someone who worked on the engineering for the SPR. Unfortunately it's fallen off the front page and I can't find it now, but:

> Also, the more water we pump in, the more salt leeches into the water and the more the bottom of the chamber deforms, creating shear forces in the upp walls that lower its overall structural integrity.

It turns out that it's trivially easy to prevent the water from leeching out the salt. They presaturate the water with salt, so that it already contains the maximum amount of salt that can be dissolved for a given temperature. When they pump the brine out, it goes into aboveground brine pools that can easily be seen on satellite imagery. The salinity of this brine can easily be controlled: if you want to expand the cavern, you mix it with freshwater so the brine dissolves more of the edges, if you don't you pump it back in as brine.

Edit: Here, found some satellite imagery of one of the SPR sites:

https://maps.app.goo.gl/B8XJ9TVhQfcdErky5

You can clearly see the brine pond, which is as big as the aboveground portion of the SPR itself.

I also think I've also replied this to you before, but +1 for the GAO report! I use the full report as my personal model yardstick on how I document technical decisions/issues for non-technical people. The PDF is attached here:

https://www.gao.gov/assets/gao-26-106918.pdf

It would be cool to see what these look like in a photo but I guess they're never empty of liquid. I wonder what happens to the oily water after we use it? Do we boil it until it evaporates?

We can't pump saturated salt solution to prevent more salt from being dissolved?

It is funny seeing how the estimates of the lower end stability vary drastically. Have seen numbers between 70 and 150 million barrels. I have just called it half way between that and think 110 million barrels is probably the lowest they should go.

Wouldn't you then need to solve the similar problem of where to store the brine in the meantime?

Yes, that's what they do. The brine is stored in huge pools next to the extraction site.

Yea man the federal government is on top of protecting civilian groundwater supplies and communicating discoveries of contamination

And indeed, already:

https://www.cnbc.com/2026/08/15/strategic-petroleum-reserve-... "Depleted strategic oil reserve nears level that raises concerns about damage to caverns, operations"

https://fortune.com/2026/08/17/depleted-us-strategic-oil-res... “U.S. strategic reserves are getting so low the drawdown threatens to damage the 60 underground salt caverns storing American oil”

Why can't they pump more water down there to create pressure?

You can’t tile circular objects at 100% efficiency and you definitely don’t want these tanks to touch.

You further need space between them with each other and the edge of your property for a host of other reasons such as being able to inspect and paint each tank. Thus looking at actual facilities is going to give you vastly more resources options than just looking at the footprint of each tank.

Funnily enough, I guess the more you cycle them, the bigger they get until they just collapse. So you have a lot of potential storage just before you have none.

id imagine if you have the location of a site that the largest pipes visible from satellite photography would be consistently scaled in some manner with the tank size. this is guess

A fellow pyanodons player I see

Another related way is to store nuclear waste. The properties (as described in this article, impermeable/self sealing etc.) sound great until the reality that water dissolves salt comes knocking and further confronts you with the reality that salty brine corrodes nuclear waste barrels...

And even helium, which is famous for its ability to leak out of almost any container you put it in.

The US formerly maintained a National Helium Reserve (https://en.wikipedia.org/wiki/National_Helium_Reserve), in fact, until we decided that a helium reserve wasn't all that useful or important.

Under ideal conditions - about 200 million years at least. In the salt, I'm not sure.

well it's been underground in similar conditions for a couple dozen million years, so I think a while

One time I heard the limited shelf life is by design to avoid consumers hoarding. Diesel OTOH fares better

It was a great plan, but all it took to foil it was one orange man in the Epstein files.

Interesting that these articles don't mention China's storage capacity, which is bigger and more crucial these days.

Maybe China publishes less official knowledge?

Probably because the oil itself has been getting pretty popular to, on account of the whole "bombing the people who control access to where we usually get it from" thing: https://www.reuters.com/business/energy/oil-stocks-us-strate...

Brine is useful to sell to industry.

AIUI, salt caverns don’t like to be filled with brine because they become more susceptible to temperature changes of the earth and pressure from surrounding rock. Both can heat the cavern, which is bad for structural integrity.

This way the US Gov can be a buyer of last resort. Backdoor bailouts.

This isn't a political article?

You complain about politics on HN in the same breath that you implore moderators to stiffle discussion that offends your politics. Do you see the hypocrisy?