English Abstract The Gorleben salt dome is overlain by Tertiary and
Quaternary sediments, which form a complex hydrogeological system of
aquifers and aquitards. In general one can recognize a lower and an upper
aquifer both consisting of sand and gravel, and an intermediate clay complex
isolating the two aquifers. In this study, the "Weisses Moor" pumping test
data are used to obtain information about the hydraulic properties of the
Gorleben system. The interpretation of the Weisses Moor pumping test will
be carried out in steps of increasing difficulty. This report contains the
results of the first step of modelling. It is assumed that the variations
in the salt concentration can be neglected and that the porous medium is
homogeneous and isotropic. Under such circumstances, the drawdowns observed
in the observation wells due to a pumping test can be described by the Theis
solution. The AQ-AT code, developed at RIVM, is used to minimize the sum of
squared differences between the observed and theoretical drawdown to obtain
optimal values of storativity and transmissivity. It appears that there are
significant differences between the optimal values calculated for various
observation wells. Therefore, the assumptions of homogeneity, isotropy
and/or constant salt concentration do not apply. These assumptions will be
relaxed in the following modelling steps in order to obtain more
satisfactory results.
