It seems to me that these deltas are talking about the Hammam that Epstein had built on his Island. I believe the "H" is for Hammam. The same Hammam that was on Isaac Kappy's deadman switch.
Here are the plans for the Hammam on the DOJ Epstein doc website. As you can see it looks just like the Hammam in Kappy's video.
https://www.justice.gov/epstein/files/DataSet%209/EFTA00803348.pdf
The builder said it was under the tennis court.
EPSTEIN ISLAND HAMMAM todays delta