Figure 3.

Profiles of groundwater (a) ³H with analytical error, (b) dissolved As, (c) ¹⁴C in DIC, and (d) ¹⁴C ages plotted against sample depth. All ³H measurements, including several repeat measurements, are shown; for samples where ¹⁴C was measured twice, ¹⁴C_DIC and calculated ages plotted in this figure, and hereafter, are based on the ¹⁴C values obtained in 2010. The grey line in (a) indicates 0.1 TU, the concentration above which all ³H samples (except for two with a large analytical error) are conclusively detectable, whereas the grey line in (b) denotes the current World Health Organization limit of 10 μg/L As in safe drinking water. The symbols in (d) show C₁ ¹⁴C age, a simple open system model that corrects for the initial ¹⁴C_DIC at recharge of 0.90 FM. The error bars indicate “UC” (uncorrected) ¹⁴C age as the maximum age, calculated directly from the measured ¹⁴C values without any correction, and C₂ ¹⁴C age as the minimum age, which contains an additional correction for the maximum contribution of radiocarbon-dead carbonate dissolution along the flowpath. In this figure, and hereafter, the pink fill in black circles indicates the shallow depth samples (A7, A8, and C5) with consistent deeper groundwater properties across various geochemical and age parameters, whereas the yellow fill in black circles denotes shallow aquifer groundwater with particularly elevated ³H concentrations (>0.3 TU).