A novel high-resolution (2–4 m source and receiver spacing) reflection
and refraction seismic survey was carried out for aquifer
characterization and to confirm the existing depositional model of the
interlobate esker of Virttaankangas, which is part of the
Säkylänharju-Virttaankangas glaciofluvial esker-chain complex in
southwest Finland. The interlobate esker complex hosting the managed
aquifer recharge (MAR) plant is the source of the entire water supply
for the city of Turku and its surrounding municipalities. An accurate
delineation of the aquifer is therefore critical for long-term MAR
planning and sustainable use of the esker resources. Moreover, an
additional target was to resolve the poorly known stratigraphy of the
70–100-m-thick glacial deposits overlying a zone of fractured bedrock.
Bedrock surface as well as fracture zones were confirmed through
combined reflection seismic and refraction tomography results and
further validated against existing borehole information. The
high-resolution seismic data proved successful in accurately delineating
the esker cores and revealing complex stratigraphy from fan lobes to
kettle holes, providing valuable information for potential new pumping
wells. This study illustrates the potential of geophysical methods for
fast and cost-effective esker studies, in particular the digital-based
landstreamer and its combination with geophone-based wireless recorders,
where the cover sediments are reasonably thick.