Solute dispersion coefficients in heterogeneous ...

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XVI International Conference on Computational Methods in Water Resources (CMWR-XVI) Ingeniørhuset

Solute dispersion coefficients in heterogeneous porous media as related with the migration of pesticides in groundwater
Paper
Author:Christos Tsakiroglou <ctsakir@iceht.forth.gr> (FORTH / ICE-HT, Stadiou Street, Platani, P.O.Box 1414, GR-26504 Patras, Greece)
Dimitra Tzovolou <dtzovol@iceht.forth.gr> (FORTH / ICE-HT, Stadiou Street, Platani, P.O.Box 1414, GR-26504 Patras, Greece)
Christos Aggelopoulos <caggelop@iceht.forth.gr> (FORTH / ICE-HT, Stadiou Street, Platani, P.O.Box 1414, GR-26504 Patras, Greece)
Maria Theodoropoulou <mtheod@iceht.forth.gr> (Technological Educational Institute of Patras, M. Alexandrou 1, GR-26334 Patras, Greece)
Theodora Dalkarani <dalkarani@teipat.gr> (Technological Educational Institute of Patras, M. Alexandrou 1, GR-26334 Patras, Greece)
Constantinos Pikios <pikios@teipat.gr> (Technological Educational Institute of Patras, M. Alexandrou 1, GR-26334 Patras, Greece)
Presenter:Christos Tsakiroglou <ctsakir@iceht.forth.gr> (FORTH / ICE-HT, Stadiou Street, Platani, P.O.Box 1414, GR-26504 Patras, Greece)
Date: 2006-06-18     Track: General Sessions     Session: General
DOI:10.4122/1.1000000733
DOI:10.4122/1.1000000734

During the last years, too much attention has been focused on problems related with the diffuse pollution of groundwater by pesticides. However, in spite of the numerous lab-scale and field-scale experimental studies and numerical approaches, one significant factor is usually overlooked: the transverse and longitudinal dispersivities are scale-dependent and sensitive to the variation of microscopic properties of the pore structure and multiscale heterogeneities. Miscible displacement and single source-solute transport experiments are performed on long columns of disturbed soils of broad grain size distribution. The geometrical and topological parameters of the pore space of soils are estimated by fitting the experimental mercury intrusion/retraction curves to analytical percolation models of the processes. The breakthrough curves of the tracer (NaCl) concentration along the column is monitored by measuring the electrical resistance at various axial positions from the column entrance. An inverse modeling algorithm based on a Bayesian estimator is used to fit the experimental data to adequate analytical and numerical solutions of the advection dispersion equation to estimate the dispersion coefficients as functions of the pore structure heterogeneity, and Peclet number. Moreover, this information is used to develop relevant phenomenological models of the longitudinal and transverse dispersion coefficients. Then, a 2-D macroscopic numerical model of the transport / sorption / biodegradation of pesticides in heterogeneous porous media is developed in the environment of flex-PDE (solver of partial differential equations with finite elements) to simulate long-term fate of pesticides in groundwater. Sample simulations are done by using literature and laboratory data concerning the physicochemical and transport properties of four pesticides (glyphosate, phorate, mancozeb, and 2,4-D) that are widely utilized in agricultural cultivations of Western Greece. The simulator is employed to investigate the potential errors caused on (1) the long-term predictions of the fate of pesticides in aquifers, and (2) the interpretation of lab-scale mobility experiments of pesticides, when incorrect values of dispersion coefficients are used as input data.