Browsing by Author "Pihko, Jekaterina"

Hyvinkäänkylä pumping station extracts groundwater from a local esker aquifer and supplies drinking water within the Hyvinkää municipality. There have been problems with the aquifer’s water quality, when surface water from the Vantaa river has mixed with groundwater during flooding season. As a result of the mixing, the pumping at the station must be periodically stopped. For more effective groundwater acquisition, management and protection it is critical to gain better understanding of the structure of the aquifer better. In addition, more knowledge of the groundwater-surface water interaction is needed and information on the possible routes of groundwater flow, particularly those which most affect the groundwater supply coming to the pumping station. The purpose of this study is to gather the previous research on the area and to create a 3D hydrogeological structural model using the Leapfrog Geo program. The model in this study visualizes the hydrogeological structures and serves as input for a groundwater flow model. The data in this study can be categorized into three groups: the structure of the bedrock and sediments, the level of the groundwater and the groundwater discharge. The structure of the bedrock and sediments was surveyed by geophysical methods, using previous data as well as some additional data gathered by field measurements. Data on the groundwater level measurements were obtained from both the Finnish Environment Institute and the Hyvinkää Water station. Additional data were collected using field measurements. To measure the amount of groundwater discharge, data were collected using flow measurements in the Vantaa River and the results compared with previous research. The geological and geophysical data were compiled and georeferenced first in ArcGis and then transferred into Leapfrog, which was used to build the 3D hydrogeological structural model. On the basis of the geological units of the drill data, five hydrogeological units were formed: coarse glaciofluvial material, fine glaciofluvial material, fine grained material, till and other. The hydraulic conductivity of the drill core sediment samples were calculated, and then used to estimate the hydraulic conductivity within and between the different sediment layers. Since one purpose for the 3D structural model was to serve as a base for the flow model, it was simplified into a 2-layer model. The study area was divided into smaller subareas, which were visualized with cross sections that were sliced from the 3D model. The measured groundwater levels were interpolated to demonstrate the groundwater flow direction in the study area. The groundwater monitoring levels were examined over a five year period and compared with weather and groundwater pumping data. The flow measurements obtained from the Vantaa River were compared to previous research to estimate the amount of groundwater discharge into the Vantaa River. The contribution of this study is five new significant observations about the structure of the aquifer: 1) the north and south part of the aquifer are connected to each other 2) the three-dimensional shape of the esker is different from its geomorphologic shape 3) most of the groundwater flowing to the pumping station is from the south side of the river 4) the amount of groundwater flowing to the pumping station is very high compared to the surface area of the aquifer 5) thick glaciofluvial layers underneath the Hirvisuo bog allow groundwater flow from the first Salpausselkä to the esker.