PREDICTING BEHAVIOR OF CONTAMINANTS IN AQUIFERS USING APPARENT RELATIVE RETARDATION OF SURROGATES

Two-well recirculating tracer tests can be used not only to determine porosity and dispersivity of aquifers, but also to compare the in situ behavior of different solutes in aquifers, thus avoiding problems of transferring laboratory-scale results to the field scale. At special f ield sites for the testing and calibration of tracers under carefully controlled conditions, the behavior of certain hazardous target contam inants can be compared to that of harmless surrogate tracers, which in turn, can be injected into other aquifers with minimal environmental risk and analyzed to determine how the hazardous substances would beha ve during normal groundwater transit and during remediation. The area under the recirculating-test breakthrough curve of each solute is comp uted and divided by the product of concentration and duration of its o riginal spike to obtain the cumulative relative mass time (CRMT) of ea ch substance for any time span after sampling begins. The apparent rel ative retardation (ARR(d)) factor is obtained as: ARR(d) = [CRMT(targe t)]/[CRMT(surrogate)]. Results of field trials in a fissured carbonate aquifer, using a tritium target and a bromide surrogate, showed how A RR(d) varied mostly with pore size. This technique can be used with ot her binary or higher-order combinations of substances.