The verification of the estimation of transport and sorption parameters in the MATLAB environment. Column test
Journal Title: Geology, Geophysics & Environment - Year 2017, Vol 43, Issue 3
Abstract
Mathematical modelling of migration of pollutants in the groundwater environment requires knowledge of the values of transport and sorption parameters. The value of those parameters can be determined by means of solving the inverse problem, which consists in finding the best fitting of the mathematical model to the results of the conducted field or column tests. The aim of this study was 1) to determine the values of the advection, dispersion and sorption parameters of selected tracers that are transported through a porous medium, and 2) to verify the applied parameters estimation procedure. The authors examined the migration of a solution containing conservative tracers (chloride ions and nitrate ions) and reactive tracers (among other: lithium ions and ammonium ions) through a sample of medium sand. The soil sample for the column test was taken from an aquifer near groundwater intake Tursko B in the village of Jedlec, Wielkopolska province, Poland. The parameters estimation procedure, conducted in the MATLAB environment, included the numerical solution of the differential equations of transport and sorption, and the application of the numerical optimization method. During the identification, the authors tested twelve mathematical models including the advection-dispersion model, as well as single and hybrid sorption models. Single sorption models included equilibrium or non-equilibrium sorption, while hybrid (i.e. two-site) sorption models combined equilibrium or non-equilibrium sorption. The optimization consisted in fitting the theoretical tracer breakthrough curve to the experimental breakthrough curve, recorded during the column test. The authors made a comparison of the parameters values obtained by means of the global and local optimization method. The fitting quality was assessed by calculating the RMSE and correlation coefficient r. As a result of the research, the authors determined the value of hydraulic conductivity k, the value of effective porosity ne, and the value of longitudinal dispersivity a. The authors found out that the nature of lithium ions migration is best captured by the single sorption model (equilibrium sorption), whereas the nature of ammonium ions migration by the hybrid model with irreversible sorption. Based on the value of retardation R the authors also found out that lithium ions on the tested soil revealed low sorption intensity, while ammonium ions showed medium intensity. The verification of parameters estimation in the MATLAB environment was carried out by comparing it against the alternative, well-known and often tested method, based on analytical solutions of the transport and sorption equation, combined with optimization within the FIELD and KLUTE-STEP programmes.
Authors and Affiliations
Monika Okońska, Mariusz Kaczmarek, Piotr Małoszewski, Marek Marciniak
Keywords
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- EP ID EP265440
- DOI 10.7494/geol.2017.43.3.213
- Views 304
- Downloads 0
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