Tunneling produces voluminous excavated materials, (aka "Spoil Dirt") -- which must be disposed of in some fashion. Spoil Dirt deposits -- and the volume thereof -- are de facto evidence of subterranean excavation.
- Spoil Dirt typically differs from surrounding surface soil in albedo, color, texture, fertility and/or angle of repose requirement.
- Most tunnelers (even quasi-clandestine ones) dispose of Spoil Dirt in thousands of overlapping dump-load piles, which produces a "pimply" appearance -- as at Iran's "Parchin" nuclear materials facility:
The color and albedo of the spoil dirt also contrasts with the natural soil surface (at lower right and bottom left center).
- Epstein and his construction engineers were more clever. They disposed of the spoil dirt from tunnel excavations by using it -- for extensive 3-D landscaping, for road building, for leveling building sites, etc.
- And -- when they had more spoil dirt than they could use -- they simply "hid it in plain sight":
- Nearly 10,000 cubic yards of spoil dirt was disposed of in that massive, "in-your-face" "berm" that surrounds the "Tennis Court" area.
- A large, but indeterminate, volume of spoil dirt was disposed by spreading it along the tops and sides of LSJI's major ridges:
Finally, an Apple Maps view that illustrates the above tunnel-identifying principles: