S. Moysey L.D. Cecil M. Zreda S.N. Davis 2003 <p><span>Natural production of the radionuclide&nbsp;</span>chlorine<span>-</span>36<span>&nbsp;(</span>³⁶<span>Cl) has provided a valuable tracer for&nbsp;</span>groundwater<span>&nbsp;studies. The nuclear industry, especially the testing of thermonuclear weapons, has also produced large amounts of&nbsp;</span>³⁶<span>Cl that can be detected&nbsp;</span>in<span>&nbsp;many samples of&nbsp;</span>groundwater<span>.&nbsp;</span>In<span>&nbsp;order to be most useful&nbsp;</span>in<span>&nbsp;hydrologic studies, the natural production prior to 1952 should be distinguished from more recent artificial sources. The object of this study was to reconstruct the probable preanthropogenic levels of&nbsp;</span>³⁶<span>Cl&nbsp;</span>in<span>&nbsp;</span>groundwater<span>&nbsp;</span>in<span>&nbsp;the&nbsp;</span>United<span>&nbsp;</span>States<span>. Although significant local variations exist, they are superimposed on a broad regional pattern of&nbsp;</span>³⁶<span>Cl/Cl ratios&nbsp;</span>in<span>&nbsp;the&nbsp;</span>United<span>&nbsp;</span>States<span>. Owing to the influence of atmospherically transported ocean salt, natural ratios of&nbsp;</span>³⁶<span>Cl/total Cl are lowest near the coast and increase to a maximum&nbsp;</span>in<span>&nbsp;the central Rocky Mountains of the&nbsp;</span>United<span>&nbsp;</span>States<span>.</span></p> application/pdf 10.1007/s10040-002-0232-6 en Springer Chlorine-36 in groundwater of the United States: Empirical data article