TY - JOUR
T1 - Effects of degree of water saturation on dispersivity and immobile water in sandy soil columns
AU - Maraqa, Munjed A.
AU - Wallace, Roger B.
AU - Voice, Thomas C.
N1 - Funding Information:
This research was supported by the National Institute of Environmental Health Sciences through grant number (08-P2ESO4911B).
PY - 1997/3
Y1 - 1997/3
N2 - Three natural nonaggregated soil samples, with similar grain-size distributions, have been used to determine the dispersive behavior of porous media under steady, saturated and unsaturated flow conditions. Tritium was used as a tracer and was found to have no sorption on the solid matrix. Generated breakthrough curves (BTCs) for the unsaturated experiments were symmetrical with no evidence of tailing. The unsaturated experiments for two of the soils were adequately described by considering all the water in the pore volume as mobile. However, about 10% of the pore water, independent of the degree of saturation, was found to be immobile in the case of the third soil during unsaturated flow. For this soil, there was no mass transfer between the two water regions, indicating that the immobile water is essentially isolated from the flowing water fraction. For all three soils, dispersivity under unsaturated conditions was found to be higher, independent of the degree of water saturation, than the value determined for the saturated experiments. This is inconsistent with what would be expected from the simple bundle-of-capillary-tubes model and does not agree well with a more sophisticated conceptualization of the porous medium. The data, however, clearly indicate a wider range in pore-water velocities when these soils are desaturated.
AB - Three natural nonaggregated soil samples, with similar grain-size distributions, have been used to determine the dispersive behavior of porous media under steady, saturated and unsaturated flow conditions. Tritium was used as a tracer and was found to have no sorption on the solid matrix. Generated breakthrough curves (BTCs) for the unsaturated experiments were symmetrical with no evidence of tailing. The unsaturated experiments for two of the soils were adequately described by considering all the water in the pore volume as mobile. However, about 10% of the pore water, independent of the degree of saturation, was found to be immobile in the case of the third soil during unsaturated flow. For this soil, there was no mass transfer between the two water regions, indicating that the immobile water is essentially isolated from the flowing water fraction. For all three soils, dispersivity under unsaturated conditions was found to be higher, independent of the degree of water saturation, than the value determined for the saturated experiments. This is inconsistent with what would be expected from the simple bundle-of-capillary-tubes model and does not agree well with a more sophisticated conceptualization of the porous medium. The data, however, clearly indicate a wider range in pore-water velocities when these soils are desaturated.
KW - Hydrodynamic dispersion
KW - Physical nonequilibrium
KW - Transport model
KW - Tritium
KW - Unsaturated flow
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U2 - 10.1016/S0169-7722(96)00032-0
DO - 10.1016/S0169-7722(96)00032-0
M3 - Article
AN - SCOPUS:0030612941
SN - 0169-7722
VL - 25
SP - 199
EP - 218
JO - Journal of contaminant hydrology
JF - Journal of contaminant hydrology
IS - 3-4
ER -