Complementary indicators have been used in developing a safety case in order to avoid uncertainties in the biosphere modeling used to estimate conventional dose or risk. For example, radionuclide fluxes can be used to evaluate the effectiveness of barrier performance. However, it is difficult to define relevant yardsticks for comparison, because the fluxes of naturally occurring radionuclides due to geological processes vary considerably depending on time and location. This paper discusses the relevance of alternative yardsticks for assessing modeled radionuclide fluxes by selecting yardsticks calculated from fluxes of natural radionuclides at the groundwater discharge point from the geosphere to an aquifer; these are then compared with fluxes of repository-derived radionuclides at the same point. Such yardsticks avoid surface geological processes that may also contribute to natural fluxes, allowing comparison at a suitable, common evaluation point that avoids dependence on site-specific conditions. The effectiveness and robustness of barrier performance is demonstrated using the developed yardsticks and the sensitivity of the analysis to groundwater flux is illustrated.