You want geology that is expected to remain stable for eons where the material will be secure from both intentional and unintentional excavation, for eons. And, more immediately, concerns over ground water contamination. Even cities like LA get some of their water supply from wells. And, more rural areas are often served by 100% ground water.

Finding sites to safely and permanently dispose of nuclear waste has been hard. Both because a lot of areas are poorly suited, and also nobody wants a permanent nuclear waste dump in their back yard.

Obviously not ever single place is suitable but it's being done now in Finland and Slovenia. The holes are 5km deep and the bottom 2km are filled before its capped. This is well below the water table in most places. A DOE analysis found that every single state in the US has suitable sites.

Great idea, let’s put it next to your well.

Sorry to reply again. The well on my family farm is a few dozen feet deep, and the bore holes are 5k feet deep and capped at a depth of 3k ft. The farm sit on a massive amount of clay, which is actually great for this kind of thing because clay seals itself under pressure. The proposed French sites are all in clay. I'd be happy to host a site there, or a similar facility near where I actually live.

A deep borehole is super deep compared to a well.