283 meters, not 2.83km. Still big though. The helium is stored underground in a salt dome (that was once full of natural gas). See here for more: https://en.

283 meters, not 2.83km. Still big though. The helium is stored underground in a salt dome (that was once full of natural gas). See here for more: https://en.wikipedia.org/wiki/National_Helium_Reserve https://en.wikipedia.org/wiki/National_Helium_Reserve