An advective-dispersive stream tube approach for the transfer of conservative-tracer data to reactive transport

Conservative-tracer data are used for the parameterization of mixing-controlled reactive transport. Temporal moments of the tracer breakthrough curve integrated over the outflow boundary of the domain yield the average velocity and the path-averaged macrodispersion coefficient. On the basis of this information alone, no distinction is possible between spreading and mixing of the tracer. Analyzing the temporal moments of breakthrough curves locally obtained at single points in the domain gives additional information about the dilution of the tracer. In an accompanying paper [Cirpka ann Kitanidis, this issue] we derive an apparent Peclet number of mixing Pe(a) from local temporal moments. Assuming that Pe(a) is constant over the cross section of the outflow boundary, a corrected probability density function of arrival times is determined. By interpreting the spatially integrated breakthrough curve as the result of advective-dispersive transport in independent stream tubes with identical Peclet number but differing seepage velocity, it is possible to transfer results of conservative transport to the transport of interacting compounds for cases in which mixing of the compounds is influenced significantly by local-scale dispersion. This is an improvement to the stochastic-convective model of Simmons et al. [1995] for the transfer of integrated tracer data to reactive transport. The approach is applied to the hypothetical case of a bimolecular reaction in a heterogeneous two-dimensional aquifer.