THREE-DIMENSIONAL HYDROGEOLOGICAL CHARACTERIZATION OF FINNISH SMALL HETEROGENOUS SEDIMENTARY AQUIFERS

In Finland, the Precambrian bedrock is covered by a thin layer of glacial and postglacial sediments, mainly till, marine or lacustrine sediments and glaciofluvial or littoral gravels and sands varying in thickness from a few to some tens of meters. Most of the Finnish aquifers are shallow, unconfined, porous sand and gravel deposits, i.e. eskers, ice-marginal end moraine complexes or minor beach terraces. In future, mapping the hydrogeological structure and hydraulic properties of potential sedimentary aquifers will be statutory according to the Water Framework Directive of the European Union.

The research was undertaken in a small, quaternary, heterogenous aquifer at Kauriansalmi in South-Eastern Finland (Hellstén et al. 2005) in order to generate practices for visualization and hydrogeological characterization of Finnish aquifers.

Hydraulic conductivity has been established in multiple scales: slug-tests and infiltration tests (single-ring and Guelphs infiltrometer) in the field, permeameter tests from soil samples in the laboratory and calculations from the grain size analyses using several methods (Etelämäki 2004).

Conceptual model was created based on the data obtained by drillings, geophysical measurements (natural gamma-logging and Ground Penetrating Radar) and hydraulic field and laboratory tests. The final 3-D visualization of the conceptual model was carried out with Surfer® and EarthVision©.

Four hydrostratigraphical units with different hydraulic properties have been observed and visualized. The 3D-hydrogeologic model will be used by Finnish Environment Institute to explain the flow conditions and the observed variability in groundwater quality in the aquifer as well as to predict the solute transport of road deicing chemicals tested in the aquifer (Hellstén et al. 2005).