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Predicting Preferential Flow of Pollutants via Fractures Using Field and Laboratory Soil Texture Data
Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.orgCitation: 2011 Louisville, Kentucky, August 7-10, 2011 1111335.
Authors: Eun Kyoung Kim, Ann D Christy, Young Woon Kang, Julie Weatherington-Rice
Keywords: Sand, Silt, Clay, Cracks, Soil physical properties, Porous media, Soil structure, Soil water movement
Fractures in glacially related fine-grained materials create preferential flow paths, allowing pollutants to infiltrate rapidly, and potentially resulting in groundwater pollution. However, it is difficult to detect fractures on site without test pit excavation and soil borings. A practical predictive model was developed based on soil texture data from over 100 sites in Ohio and results from laboratory scale fracturing experiments. In the laboratory experiments, samples of soils found to be naturally fractured in the field were mixed with increasing proportions of pure silica sand and desiccated to determine at what point the mixtures would no longer support fractures. Results were plotted on a USDA ternary diagram to define the boundaries of the fracture-prone region of soil textures. In this study, fracture-prone soil texture boundary conditions developed based on Ohio field data were re-evaluated, extended, and validated through additional sets of laboratory scale fracturing experiments on Midwestern soils from Michigan, Iowa, and a few additional Ohio sites. The results showed that glacially related fine-grained soil materials having less than 79% sand or greater than 6.5% clay are more likely to support fracturing. Agricultural engineers, geologists, and soil scientists can apply this boundary condition method to their own site-specific data to predict where fracturing is most likely to occur and thus where ground water will be most vulnerable to pollutant transport.