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Experimental Determination of Effective Diffusion Parameters in the Matrix of Fractured Till

^a Versar, Inc., 6850 Versar Center, Springfield VA 22151
^b Dep. of Geological and Atmospheric Sciences, Iowa State Univ., Ames IA 50011
^c Agronomy Dep., Iowa State Univ., Ames, IA 50011

View larger version (41K): [in a new window]   Fig. 1. Map showing the locations of the three study sites on the Des Moines Lobe (DML), Iowan Erosion Surface (IES), and Southern Iowa Drift Plain (SIDP) landform regions. Other mapped landform regions given in Prior (1991).

View larger version (35K): [in a new window]   Fig. 2. Schematic diagram of the diffusion cell apparatus.

View larger version (14K): [in a new window]   Fig. 3. Molecular structure and aqueous diffusion coefficient (D0) for Br–, PFBA, and PIPES.

View larger version (34K): [in a new window]   Fig. 4. Time-concentration plots for Br–, PFBA, and PIPES taken from four representative radial diffusion cell experiments.

View larger version (21K): [in a new window]   Fig. 5. Standard boxplots (Helsel and Hirsch, 1992) of total porosity (T) and effective diffusive porosity (De) for Br–, PFBA, and PIPES. Median values of De are significantly different from each other and from T ( = 0.05) and decrease with increasing molecular weight of the tracer.

View larger version (18K): [in a new window]   Fig. 6. Standard boxplots showing the effective diffusion coefficient (De) for Br–, PFBA, and PIPES. Median values are significantly different ( = 0.05) and decrease with increasing molecular weight of the tracer. Dotted lines indicate values of the aqueous diffusion coefficient (D0) for the tracers.

View larger version (19K): [in a new window]   Fig. 7. Standard boxplots showing the mass exchange coefficient () for Br–, PFBA, and PIPES. Median values are significantly different ( = 0.05) and decrease with increasing molecular weight of the tracer.