Field campaigns to sample groundwater were conducted in Umatilla, Oregon, USA during September 2020 and in Tucson, Arizona, USA during November 2021. Water samples for dissolved noble gas isotope measurements were collected in 6-liter (L) pre-evacuated stainless steel flasks (Restek TO-can air sampling flasks sealed with a Swagelok SS-4H valve), leaving 1 L of headspace. The sample gases were equilibrated between the dissolved phase in the sample water and the gas phase in the headspace on an orbital shaker for at least 3 days at a constant known temperature. After the sample water was drained, the headspace gas was transferred and gettered to remove non-inert gases. The remaining gas sample was measured on a dynamic isotope ratio mass spectrometer (IRMS), and the measured isotope ratios were corrected using known solubilities (Seltzer et al., 2019) and the recorded equilibration temperature to obtain the original isotope ratios of the water sample (Ng et al., 2023). Umatilla samples were stored for a year at room temperature prior to sampling. Tucson samples were stored for 2 weeks at room temperature prior to sampling.