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Interpretation of tracer tests performed in fractured rock of the Lange Bramke basin, Germany |
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| Authors: | Piotr Maloszewski Andreas Herrmann Andrzej Zuber |
| Institution: | GSF-Institute of Hydrology, Ingolst?dter Landstr. 1, D-85764 Neuherberg, Germany Fax: +49-89-3187-3361 e-mail: malosz@gsf.de, DE Institute of Geography and Geoecology, Technical University, Langer Kamp 19c, D-38106 Braunschweig, Germany, DE Institute of Nuclear Physics, ul. Radzikowskiego 152, PL-31342 Cracow, Poland, PL |
| Abstract: | Two multitracer tests performed in one of the major cross-fault zones of the Lange Bramke basin (Harz Mountains, Germany) confirm the dominant role of the fault zone in groundwater flow and solute transport. Tracers having different coefficients of molecular diffusion (deuterium, bromide, uranine, and eosine) yielded breakthrough curves that can only be explained by a model that couples the advective–dispersive transport in the fractures with the molecular diffusion exchange in the matrix. For the scale of the tests (maximum distance of 225 m), an approximation was used in which the influence of adjacent fractures is neglected. That model yielded nearly the same rock and transport parameters for each tracer, which means that the single-fracture approximation is acceptable and that matrix diffusion plays an important role. The hydraulic conductivity of the fault zone obtained from the tracer tests is about 1.5×10–2 m/s, whereas the regional hydraulic conductivity of the fractured rock mass is about 3×10–7 m/s, as estimated from the tritium age and the matrix porosity of about 2%. These values show that the hydraulic conductivity along the fault is several orders of magnitude larger than that of the remaining fractured part of the aquifer, which confirms the dominant role of the fault zones as collectors of water and conductors of fast flow. Received, April 1997 Revised, January 1998, August 1998 Accepted, August 1998 |
| Keywords: | tracer tests fractured rocks Germany diffusion analytical solutions |
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