Aziz Amoozegar, Christopher P. Niewoehner, and David L. Lindbo. Soil Science Department, North Carolina State University, Raleigh, NC 27695-7619
Groundwater samples are commonly collected from various depths below the water table to assess transport of pollutants from waste disposal areas. This may not be the best practice because the capillary fringe (the tension saturated zone immediately above the water table) may impede vertical transport of solutes from the sources in the vadose zone into the ground water. Laboratory column experiments were conducted to evaluate lateral transport of solutes in the capillary fringe above a shallow water table. A 240-cm long, 120-cm tall, and 8-cm wide column with its front made from a clear polycarbonate sheet was packed with sand. A section of 2-inch perforated well casing was installed at each side of the column to simulate drainage ditches. Six outlets were installed at the bottom of the column and used as piezometers to determine water table (saturation) level. A 30-cm wide and 20-cm deep gravel-filled cut was installed at one location on the surface of the column to simulate a septic system trench. Lateral ground water flow was established by maintaining water in the perforated pipes (i.e., the simulated drainage ditches) with one side at a slightly higher level than the other side of the column. A red dye solution was applied to the simulated trench under various scenarios, and the movement of the dye solution was recorded using time lapse photography for several days. Under all scenarios, the red dye solution from the trench moved vertically down until reaching the capillary fringe. The dye moved laterally within the capillary fringe until reaching the simulated drainage outlet. If the laboratory observations hold true under field conditions, the findings of this study will be important for developing methodologies for solute transport monitoring.
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