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141.
The point velocity probe (PVP) is a device that can measure groundwater velocity at the centimeter scale, and unlike devices that measure velocity within well screens, the PVP operates while in direct contact with the porous medium. Because of this feature, it was postulated that the PVP could be effective in measuring velocity within the capillary fringe. This hypothesis was tested using a laboratory flow-through cell filled with a medium-fine sand from Canadian Forces Base Borden. The cell was constructed to simulate conditions such that the PVP was positioned from 2.5 cm below the water table to 79 cm above the water table. As the water table was lowered, the PVP gave highly consistent values of velocity over the range equivalent to 2.5 cm below the water table to 44 cm above the water table, the approximate extent of the capillary fringe. The average measured velocity was 11.3 cm/d ± 11.6%, somewhat higher than that calculated based on the measured discharge through the cell (7.5 cm/d ± 5.5%). With a further decline in the water table there was a progressive decrease in the measured velocity values, consistent with the declining hydraulic conductivity as the sand material drained. Readings could not be made beyond about 57 cm, where the water content was approximately 75% of saturation. These experiments showed that the PVP is capable of measuring groundwater velocity within the saturated zone above the water table and possibly into the unsaturated zone. Currently, this is the only instrument available with this capability. 相似文献
142.
The objective of this research was to study the sorption and transport of bacteriophage MS-2 (a bacterial virus) in saturated sediments under the effect of salinity and soluble organic matter (SOM). One-dimensional column experiments were conducted on washed high-purity silica sand and sandy soil. In sand column tests, increasing salinity showed distinct effect on enhancing MS-2 sorption. However, SOM decreased MS-2 sorption. Using a two-site reversible-irreversible sorption model and the double layer theory, we explained that pore-water salinity potentially compressed the theoretical thickness of double layers of MS-2 and sand, and thus increased sorption on reversible sorption sites. On irreversible sorption sites, increasing salinity reversed charges of some sand particles from negative to positive, and thus converted reversible sorption sites into irreversible sites and enhanced sorption of MS-2. SOM was able to expand the double layer thickness on reversible sites and competed with MS-2 for the same binding place on irreversible sites. In sandy soil column tests, the bonded and dissolved (natural) soil organic matters suppressed the effects of pore-water salinity and added SOM and significantly reduced MS-2 adsorption. This was explained that the bonded soil organic matter occupied a great portion of sorption sites and significantly reduced sorption sites for MS-2. In addition, the dissolved soil organic matter potentially expanded the double layer thickness of MS-2 and sandy soil on reversible sorption sites and competed with MS-2 for the same binding place. 相似文献
143.