Tritium-helium-3 and tritium-based groundwater-age estimates from analyses of groundwater samples from the Great Miami buried-valley aquifer, southwestern Ohio, 1999, 2000, 2019, and 2020

The U.S. Geological Survey (USGS) in cooperation with the Miami Conservancy District, Dayton, Ohio, in 2019 and 2020 investigated the occurrence of per- and polyfluoroalkyl substances (PFAS) in groundwater from the Great Miami buried-valley aquifer (GM-BVA) of Southwestern Ohio. The 23 wells used for PFAS sampling were identified and sampled previously by the USGS National Water-Quality Assessment Program to assess the occurrence of a variety of inorganic and organic contaminants in the GM-BVA. Data in this release include tritium and tritium-helium based groundwater-age estimates from the same wells sampled for PFAS,as compiled from Hinkle and others (2010) and McMahon and others (2022). The prior (1999) sampled wells were from parts of the GM-BVA in Butler, Champaign, Clark, Greene, Hamilton, Miami, Montgomery, Shelby and Warren counties in the Great Miami River, Little Miami River, and Whitewater River Basins.
Tritium and its radioactive decay daughter product helium-3 concentrations in prior (1999) groundwater samples from 22 of 23 wells sampled by this study had previously been used to estimate the age of groundwater produced from the GM-BVA since its recharge below the water table (Hinkle and others, 2010). These estimates of groundwater ages since recharge are based on the potentially limiting assumptions that tracer transport is advective (piston-flow assumptions) and that no mixing occurs in groundwater between its recharge below the water table and where it was withdrawn from each well during sampling (Hinkle and others, 2010). The recharge date relative to samples collected by this study was computed by subtracting the estimated groundwater age in years since recharge (that was computed from the 1999 or 2000 sample) from the year that samples for PFAS analysis was collected for this study from the same wells (2019). Recharge dates estimated from a tritium-based groundwater-age category are also included in this dataset, as computed from tritium concentrations reported from samples collected during the 2019–20 companion USGS National Water Quality Program sampling (McMahon and others, 2022).