Intermediate-scale experiments and numerical simulations of transport under radial flow in a two-dimensional heterogeneous porous medium

Estimated held dispersivities from uniform and nonuniform flow tracer tests are often compared without distinction, yet the difference in the flow field is important. The difference is investigated here based on intermediate-scale experiments and numerical simulations in two-dimensional heterogeneous porous media. The scale dependence of dispersivities estimated from radial flow tracer tests in two-dimensional heterogeneous porous media and the variability of these estimates are quantified. The results presented in this paper demonstrate the difference between the scale dependence inferred from uniform flow and radial flow tracer experiments in the same random hydraulic conductivity realization. In particular, dispersivities estimated using type-curve matching from radial flow tracer experiments continue to exhibit a scale dependence, even at scales where an asymptotic constant dispersivity value applies for transport in a uniform mean flow. The discrepancy between the behavior of transport in uniform and radial flows is partly due to the converging nature of the radial flow and, more importantly, due to the small source size involved in forced-gradient tracer tests. There is substantial variability in dispersivity values estimated from different injection points at the same radial distance from the pumping well. In the range of sigma(lnK) = 1.0 to 2.5 the coefficient of variation of the dispersivity estimated at the same radial distance approaches a value of about 1.0 at radial distances much larger than the correlation scale.