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Title: Estimation and upscaling of dual-permeability model parameters for the transport of E.coli D21g in soils with preferential flow

Author
item WANG, YUSONG - University Of California
item Bradford, Scott
item SIMUNEK, JIRI - University Of California

Submitted to: Journal of Contaminant Hydrology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/31/2014
Publication Date: 2/7/2014
Citation: Wang, Y., Bradford, S.A., Simunek, J. 2014. Estimation and upscaling of dual-permeability model parameters for the transport of E.coli D21g in soils with preferential flow. Journal of Contaminant Hydrology. 159:57-66.

Interpretive Summary: The presence of macropores in the root zone can lead to the rapid transport of disease causing microorganisms to water supplies that are used to irrigate fresh produce and for drinking water. A field-scale modeling approach was developed to determine the transport of E.coli D21g in saturated soils with preferential flow under different solution ionic strength (IS) conditions. Specifically, we employed a dual permeability model to simulate observed E.coli D21g transport in soil columns with different lengths and configurations of macropores under two IS conditions. The field-scale preferential transport was then estimated as a linear superposition of the various behaviors at the column-scale. An upscaling method was subsequently developed to predict the field results from column-scale model parameters. This information will be useful to scientists, engineers, regulators and health professionals in assessing the risks of microbial transport due to preferential flow at the field-scale.

Technical Abstract: Dual-permeability models are increasingly used to quantify the transport of solutes and microorganisms in soils with preferential flow. An ability to accurately determine the model parameters and their variation with preferential pathway characteristics is crucial for predicting the transport of microorganisms in the field. The dual-permeability model with optimized parameters was able to accurately describe the transport of E. coli D21g in columns with artificial macropores of different configuration and length at two ionic strength levels (1 and 20 mM NaCl). Correlations between the model parameters and the structural geometry of the preferential flow path were subsequently investigated. Decreasing the macropore length produced a decrease in the saturated hydraulic conductivity of the fracture domain and an increase in the mass transfer between the fracture and matrix domains. The mass transfer coefficient was also found to be dependent on the configuration of the preferential flow pathway. A linear superposition approach was used to estimate field scale preferential transport behavior for hypothetical fields with different amounts and configurations of macropores. Upscaling procedures were numerically investigated to predict this field scale transport behavior from column scale parameters. The upscaling method provided a satisfactory prediction of the field results under the tested scenarios. This information will be useful in assessing the risks of microbial transport due to preferential flow.