Kirsten Faulkner Peter B. McMahon Andrew G. Hunt Gerolamo C. Casile Megan B. Young Kenneth Belitz Bryant C. Jurgens 2022 <div id="Abs1-section" class="c-article-section"><div id="Abs1-content" class="c-article-section__content"><p>The distribution of groundwater age is useful for evaluating the susceptibility and sustainability of groundwater resources. Here, we compute the aquifer-scale cumulative distribution function to characterize the age distribution for 21 Principal Aquifers that account for ~80% of public-supply pumping in the United States. The aquifer-scale cumulative distribution function for each Principal Aquifer was derived from an ensemble of modeled age distributions (~60 samples per aquifer) based on multiple tracers: tritium, tritiogenic helium-3, sulfur hexafluoride, chlorofluorocarbons, carbon-14, and radiogenic helium-4. Nationally, the groundwater is 38% Anthropocene (since 1953), 34% Holocene (75 – 11,800 years ago), and 28% Pleistocene (&gt;11,800 years ago). The Anthropocene fraction ranges from &lt;5 to 100%, indicating a wide range in susceptibility to land-surface contamination. The Pleistocene fraction of groundwater exceeds 50% in 7 eastern aquifers that are predominately confined. The Holocene fraction of groundwater exceeds 50% in 5 western aquifers that are predominately unconfined. The sustainability of pumping from these Principal Aquifers depends on rates of recharge and release of groundwater stored in fine-grained layers.</p></div></div> application/pdf 10.1038/s43247-022-00473-y en Springer Nature Over a third of groundwater in USA public-supply aquifers is Anthropocene-age and susceptible to surface contamination article