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Foster, Allan W. 1 ; Randell, Jackie 2 ; Schade, Declan 3 ; Singha, Kamini 4

1 Hydrologic Science and Engineering, Colorado School of Mines
2 Hydrologic Science and Engineering, Colorado School of Mines
3 Geology and Geological Engineering, Colorado School of Mines
4 Geology and Geological Engineering, Colorado School of Mines

The advection-dispersion equation (ADE) fails to describe solute transport processes when applied to many natural systems. Here, we explore the relationship between mobile and less-mobile pore space and its physical and geochemical effects on solute transport in a series of controlled 1-D column and 3-D tank scale experiments. The objective of this research is to quantify phenomena controlling solute transport in four different grain packings, including homogeneously and heterogeneously packed Accusand, which contains no intragranular pore space, and zeolite and amorphous silica glass, both containing intragranular pore space. Experiments include injection of either potassium bromide (KBr) or lithium bromide (LiBr) tracers at volumetric flow rates ranging from 1.1 mL/min to 25 mL/min with injection times ranging from 0.5 hours to 80 hours dependent on system length and packing configuration. These tests also consist of collecting bulk conductivity geophysical measurements to help parse the relationship between the mobile and less-mobile pore space. Results indicate that heterogeneously packed and dual-porosity intragranular systems experience tailing, a transport phenomena described by highly asymmetrical breakthrough curves. The numerical models STAMMT-L, MODFLOW, and MT3DMS are used to estimate the parameters controlling transport through forward modeling and observed data inversions; we simulate homogeneous Accusand systems with breakthrough curves similar to the ADE where heterogeneous and dual-porosity intragranular systems do not. The differences in results between observed and simulated data from systems at both the column and tank scale present the need for exploration into quantifying the relationship between mobile and immobile pore space and its effect on solute transport.






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