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An official website of the United States government

Dot gov

Official websites use .gov

A .gov website belongs to an official government organization in the United States.


Secure .gov websites use HTTPS

A lock ( ) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites..

Underground Building

A building for which 50% or more of the Actual Cash Value (ACV), including machinery and equipment that are part of the building, is below ground.

Last updated March 5, 2020