We know the US government did a lot of testing of atomic bombs in the years after WWII and that many of these tests were done above ground. That these tests were pumping dangerous levels of fallout into the environment was less well-known, except to Eastman Kodak and other photographic film companies.
Kodak was first made aware of the fallout issue in 1946 when customers complained of fogged film. Investigation showed that Indiana corn husks used as packing materials were contaminated with the radioactive isotope iodine-131 (I-131). They told no one.
Then in January of 1951, following a test in Nevada, Kodak scientists detected spiked radiation levels in a snowfall that measured 25 times the norm (Kodak measured 10,000 counts per minute of radiation, compared to recent unaffected snowfalls that registered only 400). Note, this was 1,600 miles away from the test site. This time they quietly informed the Atomic Energy Commission and an industry group of their findings. The AEC did basically nothing until Kodak threatened to sue them, at which time they promised to keep Kodak and other photographic film companies aware of when they were testing along with sending meteorological information to help predict when fallout might reach them. The AEC told no one else.