Effects of the investigation scale on pumping test results in heterogeneous porous aquifers

Abstract

At the environmental field site Horkheimer Insel numerous pumping tests were performed at different investigation scales. The measured time-drawdown curves exhibit a characteristic segmentation into two or three drawdown phases. Since the site is highly heterogeneous it was intended to take advantage of the non-stationarity of the flow field during pumping tests in order to determine the effective length scale of the subsurface heterogeneity structure. The time-drawdown curves were evaluated using the Theis' analytical solution, which, however, yields different aquifer parameters for the different drawdown phases. Because this solution does not satisfy the properties of the test site aquifer totally, some of the inferred parameter distributions are regarded as suitable only for a relative comparison rather than representing ‘true’ effective parameters. Based on a definition of spatial and temporal scale, a statistical description along with a qualitative interpretation of the parameter distributions determined is provided. The results indicate that the effective length scale of the heterogeneity structure can be estimated from pumping test data. However, it is believed that for a quantitative interpretation of the field data, the application of numerical methods is necessary.