When the adsorption processes affecting the migration rates of organic solutes in groundwater systems are considered in detail, it can be shown that the use of multiple tracers should allow accurate calculation of the groundwater velocity even when all the tracers are retarded to some extent by interactions with mineral surfaces in the aquifer and even when the extent of that retardation is not known beforehand. It should be required only that the tracers be members of a series of compounds whose surface interaction energies vary regularly, this condition being met, for example, by compounds in the series C2ClnF6−n Experimental studies aimed at testing this concept show that two series of tracers behave as expected on laboratory columns (limestone and sand), thus indicating the fundamental validity of the approach. Further, the nature of the interactions between the mineral surfaces and the tracer molecules can be shown in these cases, at least, to be nonspecific, the strength of the interaction depending only on the polarizability of the tracer molecule. It seems likely that other satisfactory tracers can be selected using this criterion and that the approach should be applicable even to systems involving many different mineral surface types.