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Quantifying the Effects of Small-Scale Heterogeneities on Flow and Transport in Undisturbed Cores from the Hanford Formation

^a Environmental Sciences Division, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN, 37831-6038
^b Environmental Dynamics and Simulation, Environmental Molecular Sciences Laboratory, Pacific Northwest Laboratory, Richland, WA

View larger version (27K): [in a new window]   Fig. 1. A stratigraphic column of the vadose zone at the 200W Area Environmental Restoration Disposal Facility on the Hanford Reservation. Note that the undisturbed cores used in this study were collected in August 2000 at the 18.24-m (60-ft) depth.

View larger version (83K): [in a new window]   Fig. 2. Excavation into the Hanford Formation at the 200W Area Environmental Restoration Disposal Facility on the Hanford Reservation, 20-m depth. (a) Unconsolidated alternating layers of coarse and fine sands. (b) Expanded view of fine-grained layer from which cores were collected. Note small-scale clay layering.

View larger version (69K): [in a new window]   Fig. 3. Harvesting of undisturbed cores from the Hanford Formation. (a) Paraffin wax–coated horizontal core, and (b) sculpting of vertical core.

View larger version (98K): [in a new window]   Fig. 4. Experimental apparatus for conducting unsaturated flow experiments in undisturbed cores.

View larger version (7K): [in a new window]   Fig. 5. Chemical structure of two large organic molecules that are used as nonreactive tracers. (a) Pentafluorobenzoic acid (PFBA) and (b) piperazine-1-4-bis(2-ethanesulfonic acid) (PIPES).

View larger version (12K): [in a new window]   Fig. 6. Moisture retention functions of disturbed sediments of Hanford Formation. Symbols represent observed data. (HFV = Hanford fine material collected near the vertical core, HFH = Hanford fine material collected near the horizontal core. The number denotes the number of replicate experiments).

View larger version (19K): [in a new window]   Fig. 7. Observed (symbols) and model fitted (lines) tracer effluent concentrations involving the displacement of Br-, PFBA, and PIPES through saturated cores. Modeled Br- relative concentrations are shown with model parameters provided in Table 5. Modeled PFBA and PIPES were omitted to improve clarity of figure, since no significant difference in modeled BTCs were observed.

View larger version (21K): [in a new window]   Fig. 8. Observed tracer effluent concentrations involving the displacement of Br- through saturated and unsaturated cores. (a) Breakthrough curve (BTC) for the horizontal core under saturated and unsaturated conditions. (b) BTC for the vertical core under saturated and unsaturated conditions.

View larger version (29K): [in a new window]   Fig. 9. (a) Observed (symbols) and model fitted (lines) tracer effluent concentrations involving the displacement of Br-, PFBA, and PIPES through the unsaturated horizontal core. Modeled Br- concentrations are shown with the model parameters provided in Table 5. Modeled PFBA and PIPES concentrations were omitted to improve clarity of figure. (b) Observed initial tracer breakthrough showing separation and crossover of tracers. (c) Observed tracer concentration during washout showing separation and crossover of tracers.

View larger version (25K): [in a new window]   Fig. 10. (a) Observed (symbols) and model fitted (lines) tracer effluent concentrations involving the displacement of Br-, PFBA, and PIPES through the unsaturated vertical core. Modeled Br- concentrations are shown. Modeled PFBA and PIPES were omitted to improve clarity of figure. (b) Separation of tracers before the flow interruption in the unsaturated vertical core experiment. Model parameters are provided in Table 5.