No abstract

Three criteria for the experimental design of parameter estimation are compared by using the criteria to develop sampling patterns for determining parameter values in one‐dimensional transport models. The models include advection, dispersion, and matrix diffusion, the latter being an important process for nuclear waste isolation. The effectiveness of various designs is assessed by studying expected errors of parameter estimates and correlation between parameters. The correlations and expected errors are computed using parameter sensitivities, and the results demonstrate that the choice of design criterion can make a significant difference in the expected estimation error of parameter values in sparse designs. The best overall choice is D‐optimality, which is a measure of the volume of the joint confidence ellipsoid of the parameter estimates. E‐optimality, which minimizes the longest axis of the confidence ellipsoid, gives somewhat similar results but is not as robust for all of the estimated parameters. It is also shown that approaches that consider parameter sensitivities, but not correlation between parameters, may result in inferior designs.

As part of the Swedish site investigations and research associated with the disposal of spent nuclear fuel, tracer experiments in deep boreholes have been employed in order to characterize solute transport and hydraulic connectivity in the fractured bedrock at two sitesForsmark and Laxemar-Simpevarp. Performance and analytical results are presented from a suite of tracer experiments in varying scales, from single-hole injectionwithdrawal tests, intermediate-scale tests with sorbing tracers, to large-scale connectivity tests over distances up to several hundred meters in major fracture zones or networks of zones. In addition to demonstrating transport connectivity over large distances, a general result is that the single-hole tests, as well as the cross-hole tests with sorbing tracers, have clearly demonstrated the process of solute retention of water-conductive features in the rock at different scales.