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-contro lled reactive transport. Temporal moments of the tracer breakthrough curve integrated over the outflow boundary of the domain yield the average veloci ty 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 locall y obtained at single points in the domain gives additional information abou t the dilution of the tracer. In an accompanying paper [Cirpka ann Kitanidi s, this issue] we derive an apparent Peclet number of mixing Pe(a) from loc al temporal moments. Assuming that Pe(a) is constant over the cross section of the outflow boundary, a corrected probability density function of arriv al times is determined. By interpreting the spatially integrated breakthrou gh curve as the result of advective-dispersive transport in independent str eam tubes with identical Peclet number but differing seepage velocity, it i s possible to transfer results of conservative transport to the transport o f interacting compounds for cases in which mixing of the compounds is influ enced significantly by local-scale dispersion. This is an improvement to th e stochastic-convective model of Simmons et al. [1995] for the transfer of integrated tracer data to reactive transport. The approach is applied to th e hypothetical case of a bimolecular reaction in a heterogeneous two-dimens ional aquifer.