HR: 14:30h
AN: B23C-04    [Abstracts]
TI: Measurement of transverse dispersion and reaction in heterogeneous porous media under transient flow conditions
AU: Grathwohl, P
B23C-04 AF: Center for Applied Geoscience, University of Tuebingen, Sigwartstr. 10, Tuebingen, 72076 Germany
AU: * Piepenbrink, M
EM: matthias.piepenbrink@uni-tuebingen.de
AF: Center for Applied Geoscience, University of Tuebingen, Sigwartstr. 10, Tuebingen, 72076 Germany
AU: Eberhardt, C
B23C-04 AF: Center for Applied Geoscience, University of Tuebingen, Sigwartstr. 10, Tuebingen, 72076 Germany
AU: Kasper, M
B23C-04 AF: Institute of Physical and Theoretical Chemistry, University of Tuebingen, Auf der Morgenstelle 15, Tuebingen, 72076 Germany
AU: Gauglitz, G
B23C-04 AF: Institute of Physical and Theoretical Chemistry, University of Tuebingen, Auf der Morgenstelle 15, Tuebingen, 72076 Germany
AB: Natural attenuation (mainly biodegradation) of organic pollutants in groundwater often depends on mixing of electron donors and acceptors in the plume fringes, the spatial distribution of these highly reactive zones, compared to the volume of the whole plume, is quite small and characterized by steep concentration gradients. Mixing in the field is the result of transverse dispersion, which is a function of groundwater flow velocity, the typical length scale in the aquifer (e.g. grain size) as well as the aquifer heterogeneities, and the dynamics of the natural flow system. The objectives of this work are to investigate dispersion-limited reactions in well-controlled bench-scale experiments i.e. to elaborate how heterogeneities and transient conditions at the field scale (in time and space) influence the overall natural attenuation rates of organic pollutants in groundwater. Experiments in which (a) the spreading of a conservative tracer cloud or (b) the reaction of two reaction partners at the plume fringe is limited by transverse dispersion are currently investigated in the lab. As the quantification of transverse dispersivities in heterogeneous media under transient flow conditions requires monitoring with high resolution in space and time new optical tools (CCD camera) are employed for the quantitative mapping of the plumes.
The first experiments were conducted at bench scale using a continuous injection of a conservative colour tracers (fluorescine), which show absorption only at a specific range of wavelengths in the visible spectrum, a quantification of this tracers is thus possible by its colour depth. Quality control of the quantification obtained by the CCD set-up is done via conventional sampling and analysis at the outlet ports during steady state flow conditions. Currently, well controlled acid-base reactions, are monitored by the colour changes of pH-indicators.
This efficient spatially and time-resolved monitoring of concentration gradient changes by the CCD set-up finally provides the high resolution data required for the validation of numerical modelling. Therefore the data acquisition of these experiments will consequently be followed by the comparison to modelling results obtained by the reactive transport code PHT3D (Prommer et al., 2003, http://www.pht3d.org). This code combines the transport simulator MT3DMS (Zheng and Wang, 1999) with the geochemical model PHREEQC-2 (Parkhurst and Appelo, 1999) and was proven to be suitable to resolve the steep concentration gradients which occur at the plume fringes.
This work was funded by Deutsche Forschungsgemeinschaft, Research Group 525 "Analysis and modelling of diffusion/dispersion-limited reactions in porous media".
DE: 0412 Biogeochemical kinetics and reaction modeling (0414, 0793, 1615, 4805, 4912)
DE: 0452 Instruments and techniques
DE: 0466 Modeling
SC: Biogeosciences [B]
MN: Fall Meeting 2005