Browsing by Subject "Hyrylä"

The study area is Hyrylä groundwater area, located in southern Finland, in the city center of Tuusula. Hyrylä groundwater area is class 1 groundwater area, and it is classified as a chemical risk area. The Koskenmäki water pumping plant, owned by Keski-Uudenmaan Vesi Kuntayhtymä, is in the groundwater area, where on average 1000 m3 of water is pumped daily for domestic use. The groundwater area is situated in a southwest to northeast orientated esker which is a part of a bigger esker series starting from I-Salpausselkä in Hyvinkää. There is a big southwest to northeast orientated shear zone in the bedrock under the groundwater area where Lake Tuusulanjärvi and Tuusula-river follow the shear zone. The aim of this study was to research the interactions between river water and groundwater in the Hyrylä groundwater area and to get a better understanding of the geology of the area. Additionally, the movements of the groundwater were studied. Based on earlier studies the groundwater is discharging to the Tuusula-river near the Koskenmäki water pumping plant and the river water has been recharging to the groundwater. There are contaminated areas surrounding the old gas station in Hyrylä, where the soil and groundwater are contaminated with oil hydrocarbons, hence it was important to study where the water to Koskenmäki water pumping plant is coming from. Effects of the shear zone to the movements of the groundwater and to the amount of water available for pumping were also examined. The groundwater-river water interactions were studied with thermal methods and seepage meters. Isotopic and chemical tracers were analyzed from the water samples, which were collected from the groundwater observation wells, groundwater discharging to Tuusula-river and from the river water itself. A 3D geological structure model of the groundwater area was made based on earlier gravimetric measurements and drillhole data. The water table measurements from the observation wells were taken at the same time when the water samples were collected. Based on the 3D structure model a groundwater flow model was made to explain the movements of groundwater in Hyrylä. The geology of the groundwater area was examined with ground-penetrating radar, but the measurements were not successful and did not give any useful data for making the 3D model. The results of this study show that the groundwater is discharging to the Tuusula-river near the Koskenmäki water pumping plant. Based on the water analyses done, there was only one water sample with surface water mixed in it. 3D modeling gave a clear picture of the bedrock surface and cross-sections of the soil structure. According to the groundwater flow model, groundwater is flowing to the Koskenmäki water pumping plant from southeast. To the shear zone groundwater flows mostly from east and southeast. From the northwest part of the groundwater area the groundwater is flowing via northeast to the northern parts of the shear zone. The contaminated areas are not in the flow path to Koskenmäki water pumping plant. Based on the water analyses, groundwater discharging to the western parts of Tuusula-river is from a different source than the water discharging to the eastern parts of the river. In the shear zone the groundwater flow direction is to the south and the groundwater discharges to the river southwest of the Koskenmäki water pumping plant.