The Turku Region Artificial Infiltration Project, Finland – Tools for Enhanced Aquifer Characterization

The city of Turku and its neighboring municipalities are located in Southwestern Finland. The area has a
population of 300 000 inhabitants. The present water supply of the area relies on chemically treated river
water. The surface water supply will be replaced with artificially infiltrated groundwater in year 2011. The
project will be one of the largest managed aquifer recharge projects in Northern Europe.

The water to be infiltrated will be obtained from the River Kokemäenjoki, located 90 kilometers north from
the Turku area. The artificial infiltration will take place in the Quaternary esker aquifer called the
Virttaankangas aquifer.

Extensive geological, sedimentological, geochemical, and hydrogeological studies have been carried out in
the Virttaankangas aquifer. However, the internal variety of the hydraulic conductivities in the coarsest part
of the esker needed to be mapped in greater detail prior to the one year test pumping period with river
water in 2010. The results will be used to update the existing groundwater flow model.
The studies conducted for detailed aquifer characterization included sedimentological modeling, GPRsoundings,
drillings, and tracer tests. These studies were focused on the coarsest part of the aquifer,
depicted as the glaciofluvial coarse unit in the 3D hydrogeological model. The structures of the 3D model
units will be integrated with groundwater flow model. In short, the aim was to focus on the area where the
infiltration and water intake takes place. The sedimentological and GPR studies provided detailed
structures of the esker core, subaquous fans, and morphologically undetectable kettle holes, whereas the
tracer test verified the flow paths and residence times of the infiltrated groundwater within those
structures. All these data will be used to explicitly describe the variation of hydraulic conductivities of the
aquifer in groundwater flow model.