CAPILLARY-WICK UNSATURATED ZONE SOIL PORE WATER SAMPLER

Existing unsaturated zone soil water samplers have several deficiencies that jeopardize their utility for field sampling. Suction cups function only when a vacuum is applied, and sample from an unknown volume of soil. Pan samplers sample only saturated flow. A capillary-wick sampler was developed to overcome these problems and was tested in both the laboratory and field to evaluate its performance. Breakthrough curves for selected inorganic ions and organic chemicals were established in the laboratory. No adsorption/desorption of these chemicals was found for the capillary-wick sampler made entirely of glass. Banks of eight capillary-wick samplers were installed in field plots of Padina sand (loamy, siliceous, thermic, Grossarenic Paleustalf), Weswood silt loam (fine-silty, mixed, thermic Fluventic Ustochrept), and Lufkin clay (fine, montmorillonitic, thermic Vertic Albaqualf) soils. Saturated soil Br breakthrough curves were determined at each location and used to estimate the number of samplers required to characterize the flow of contaminants. To achieve 95% confidence in the chemical data from the three soils and plot sizes tested, 31 samplers were required for the sandy soil, six for the silt loam soil, and only two for the clay soil. The wick-activated sampler collected soil solution samples from soils having soil water potentials ranging from 0 to -6.0 kPa. The capillary-wick sampler collected samples continuously across this range of water potentials without the need for a continuous vacuum and is thus an improvement over existing samplers. While the capillary-wick samplers usually collected sample volumes representative of the flux at potentials of -5 kPa, samples collected at greater and lesser potentials were not representative of the flux.