[Bedon292]

Are you separating digging holes from drilling holes? Digging out something like a mine for people to be in to that depth is definitely hard and you are right there is a very limited number of those.

That is not really what the article is discussing though. They are talking about putting it down a drilled hole, and a mile is a very common depth for drilling. In a USGS publication summarizing deep wells in the US through 1998 [1], it talks about a dataset of more than 20,000 wells over 15,000ft (4,572 m), more than 1,000 wells over 20,000ft (6,096 m), and 52 over 25,000ft (7,620 m).

[1] https://pubs.usgs.gov/dds/dds-067/CHB.pdf