Abstract
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.
Highlights
Eskers, defined as stratified sediments of gravel and sand deposited by glacial melt-water streams (Banerjee and McDonald 1975; Shreve 1985; Hebrand and Åmark 1989; Gorrell and Shaw 1991; Warren and Ashley 1994; Huddart et al 1999; Brennand 2000), are hydrogeological settings of great significance in areas that have undergone glaciation such as in Finland, Sweden, the British Isles, USA and Canada
Turku Region Water Ltd, personal communication, 2014) is shown as a blue-white dashed line on the tomography sections and in most places matches well the tomography results; near surface velocities are expected to be extremely sensitive to the dry/saturated sediments interface found in the vicinity of the water table, the velocity model does not follow the water-table boundary in some areas
The 200-m-long prototype landstreamer system was tested for its suitability for hydrogeological characterization of the complex interlobate esker deposits down to bedrock
Summary
Eskers, defined as stratified sediments of gravel and sand deposited by glacial melt-water streams (Banerjee and McDonald 1975; Shreve 1985; Hebrand and Åmark 1989; Gorrell and Shaw 1991; Warren and Ashley 1994; Huddart et al 1999; Brennand 2000), are hydrogeological settings of great significance in areas that have undergone glaciation such as in Finland, Sweden, the British Isles, USA and Canada They are remarkable aquifers that are often used for construction aggregates, an accurate understanding and subsurface delineation of the large-scale structures as well as hydrogeological units within these precious groundwater reservoirs is essential for their environmental and economic usage (Boucher et al 2015; Nadeau et al 2015). These complexes demand deep penetrating investigation methods that can provide a link between bedrock surface topography and large-scale esker elements in order to reliably model hydrogeological units as well as the related groundwater flow
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