That's a wonderfully evocative image, and I am a total non-expert so this sort of depth may be common, but I do note that that map pin is in what looks like har

That's a wonderfully evocative image, and I am a total non-expert so this sort of depth may be common, but I do note that that map pin is in what looks like harbor landfill. It may require an unusually deep foundation to reach bedrock there.