For the non-sorbing tracer uranine, both the finite and the semi-infinite populations play a distinct role in controlling BTC. For the sorbing tracers Cs and Rb the finite population does not saturate, but acts essentially semi-infinite, thus the BTC behaviour is comparable to that obtained for a model containing only a semi-infinite rock matrix. The ability to match BTC for both sorbing and non-sorbing tracers for these three different SWIW data sets demonstrates that the two-population complex fracture model may be useful to analyze SWIW tracer test data in general. One of the two populations should be the semi-infinite rock matrix and the other finite blocks that can saturate. The latter can represent either rock blocks within the fracture, a fracture skin zone or stagnation zones.