Beneath the thick clay soil of Kurikka, in the world’s oldest valley (1.5 billion years old), lies an exceptionally vast groundwater deposit. From this deposit emerges Finland’s purest water. This water source has been under study for over a decade, and research continues.

Kurikka’s soil is predominantly clay, which can pose challenges for construction. However, this thick clay layer is a boon for groundwater: impurities from the earth’s surface are unable to permeate the clay-silt barrier, preserving the quality of the deep groundwater.

In 2010, the Geological Research Center GTK, in collaboration with Kurikka’s water supply, initiated test drilling in Kuusistonloukko. From the initial drillings, it became evident that this wasn’t a typical groundwater area.

Where does the water come from?

At Kakkuri’s springs in Kurikka, water naturally springs forth from a hole drilled through the moraine and clay, propelled by its intrinsic pressure. Over 200 groundwater observation pipes have been installed around Kurikka. The purpose of research is to determine the actual extent of the deep groundwater deposit and assess sustainable consumption and utilization levels.

The impermeable nature of the clay layer means that rainwater doesn’t accumulate in the usual manner. The water is believed to originate from the Lehtivuori area, situated more than 190 meters above sea level. Favorable soil conditions allow the water to travel through appropriate sediment layers of sand and gravel, where it accumulates.

GTK specialist researcher Mr. Niko Putkinen describes this groundwater deposit as a “geological miracle.”
– Beneath the clay loams is an ancient, deeply eroded bedrock fracture system filled with sediments from the ice ages. Specifically, these sediments are conducive to groundwater storage, such as sand and gravel, as Mr. Putkinen highlighted in an interview with YLE.

Why is this water source significant?

The Kurikka groundwater deposit stands out: no other similar and equally expansive groundwater deposit formed in rock depressions has been discovered, either in Finland or globally. The soil deposits contain vast water quantities, and the studied area spans approximately 15 x 25 kilometers.

Observation tubes monitoring the groundwater level extend to nearly 130 meters at their deepest, fortified with rock reinforcement. Each observation tube is fitted with sensors responsible for measurement, data storage, and wireless data transmission to databases.

Finnish geologists are collaborating technologically with their British counterparts. As a testament to its significance, the BBC even covered Kurikka’s situation a few years ago.