Columbia subject headings:
Earthwork--Law and legislation--United States.
Natural gas pipelines--Law and legislation--United States.
Natural gas pipelines--United States--Communication systems.
Telecommunication systems--United States.
Underground factories--United States--Communication systems.
Harvard subject headings:
Earthwork--Law and legislation--United States.
Natural gas pipelines--Law and legislation--United States.
Natural gas pipelines--United States--Communication systems.
Telecommunication systems--United States.
Underground factories--United States--Communication systems.
Princeton subject headings: