Derivation of organic carbon reactivity in a redox-stratified aquifer-hydrogeochemical modelling of kinetically driven reaction systems [Ableitung der Reaktivit?t von organisch gebundenem Kohlenstoff in redoxzonierten Grundwasserleitern - Hydrogeochemische Modellierung kinetisch angetriebener Reaktionssysteme]

摘要

Within a multitude of groundwater catchment areas, ground- and raw water quality depend foremost on the reaction between organic carbon and dissolved oxidants, in particular O_(2(aq)), nitrate und sulphate. Although the redox reactions between organic carbon (as the reductive agent) and the oxidants follow the principles of chemical thermodynamics, they are often kinetically inhibited. Modelling of concentration changes in ground- and raw water quality using hydrogeochemical reactive transport models therefore requires an imple-mentation of the kinetically-limited oxidation of organic carbon. As illustrated by the case study at Forstwald (Krefeld, Germany), it is demonstrated how organic carbon reactivity can be derived from routinely measured groundwater data and implemented in a reactive transport model using the program PhreeqC. Based on equilibrium chemistry of aqueous solutions including minerals and gases, equilibrium calculations are coupled with a dual Michaelis-Menten-kinetic model to simulate the sequential oxidative degradation of solid-state, non-mobile organic carbon along the flow path. The model is verified by comparing measured and modelled data of temporal and spatial development of groundwater quality.