ON THE TRANSPORT OF REACTIVE SOLUTES IN PARTIALLY SATURATED HETEROGENEOUS ANISOTROPIC POROUS FORMATIONS

First-order analysis, based on a stochastic continuum presentation of the Eulerian retarded velocity in heterogeneous, partially saturated p orous formations and a general Lagrangian description of the transport , was used to investigate the effect of both the anisotropy of the for mation and the texture of the soil materials constituting the formatio n, on the spreading of reactive (sorptive) solutes under unsaturated f low. The physically plausible situation in which the retardation facto r is negatively correlated with log-unsaturated conductivity was consi dered in this study. Results of the analyses show that for a given wat er saturation and gravity-dominated unsaturated flow, both the physica l and chemical heterogeneities of the formation enhance the spreading of the reactive solute in the longitudinal direction. This applies esp ecially in formations with typical flow barriers which are small in a direction perpendicular to the mean flow, relative to their size in th e direction parallel to the mean flow (large aspect ratio, e), and in formations of fine-textured soil materials with significant capillary forces (large macroscopic capillary length scale, lambda). The relativ e impact of the chemical heterogeneity of the formation on the spreadi ng of the reactive solute, however, is expected to increase in formati ons of coarse-textured soil materials (small lambda) and in formations which exhibit a significant stratification (small e). This result ste ms from the fact that when the mean flow is vertical, small lambda and small e both diminish the impact of the heterogeneity in the physical properties of the formation on the variability of the flow in the lon gitudinal direction.