CONTRACT: a numerical tool for contaminant transport and chemical transformations

Groundwater pollution control has become a growing challenge to water resources management. In this context groundwater research has to cope with the task of describing the processes influencing the input, spreading and chemical transformations of contaminants in aquifers in a quantitative manner, both as individual and as interactive processes. In this context numerical simulation of groundwater flow, contaminant transport and chemical transformations is of primary importance because it provides the opportunity to integrate such different disciplines as hydromechanics, geology, chemistry and microbiology on a common quantitative basis. It also permits coupling of the results from field measurements to those from classical laboratory experiments for the prediction of field-scale reactive behaviour. Without numerical models the effects of single processes in complex interaction in reactive transport could hardly be distinguished. Therefore numerical simulation is an indispensable tool for present-day groundwater research. As a prerequisite for the application of numerical methods, it must be ensured that the numerical tools used lead to a correct solution of the mathematical problem. Discretization errors leading to numerical diffusion or oscillatory behaviour may lead to erroneous results which may be misinterpreted as effects of chemical or physical processes. Requirements for the stability, the accuracy and the efficiency of the numerical methods are more strict and more difficult to fulfill for reactive transport than for conservative transport. The present report written by Olaf Cirpka serves as an introduction to numerical methods for reactive multicomponent transport. Special emphasis is given to discretization methods for transport, and extensive comparisons of different approaches are presented. The given test cases for reactive transport indicate that conceptual models, such as the macrodispersion model or the two-domain approach, which are commonly used for conservative transport, may lead to incorrect results when applied to the transport of compounds which react with each other. However, the test cases also reveal the differences in qualitative behaviour between reactive transport and reactive systems in fully-mixed batch reactors. (orig.)SIGLEAvailable from TIB Hannover: RA 1064(87)+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman