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Fig. 3. Expected residual tritium activities in 2001 for water originating as local annual precipitation between 1953 and 2001. Isotopic decay based on a 12.43-yr half-life was applied to a constructed tritium record to obtain this plot. The constructed record included local data (from Lincoln, NE; Ames, IA; and on-site), a trend in the local data, and estimates for missing years based on records from St. Louis, MO and Ottawa, ON, Canada, as specified in Table 3. Precipitation data are from International Atomic Energy Agency (1992), International Atomic Energy Agency and World Meteorological Organization (2001), and Simpkins (1995).
