Background radioactivity levels in Niigata city area were studied through the years of 1981-1984. As the results, it was found that the gross β-radioactivity in underground (well) water samples were comparatively higher than those of other ground water samples. Ion chromatographic and γ-ray spectroscopic determination revealed that this higher radioactivities were contributed by 40K rather than radium or thorium series nuclides or fallout originated 90Sr.
