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In the early 1980s St. Louis
experienced a rash of street
cave-ins due to
under-the-surface
erosion from old
sewers and water conduits.
A fledgling engineering firm,
EnTech Engineering Inc., was
asked if it could detect sites
where collapses might occur.
That was right down EnTech's
alley, so to speak. Nondestructive
testing with an
infrared sensing system was its
specialty.