The water supply of the city of Elverum depends on the waterworks of Grindalsmoen that is based on groundwater extraction. The background concentration of iron and manganese may in certain places be high. Thus, an in-situ treatment (Vyredox) is installed at the waterworks, producing good water supply quality. The municipality plans to expand the pumping rate due to the increasing population. In this thesis the properties and the geometry of the Grindalsmoen phreatic aquifer were studied and a groundwater flow model in GMS was developed. Furthermore, chemical analysis for water samples from the area was conducted, to investigate the water quality. Near surface geophysical surveys and data from geotechnical drillings showed that the sediment thickness of the western part of the catchment ranges between 2-7 m while the thickness close to the Glomma river banks is up to 35 m. Therefore, the western part of the catchment was cut and only the eastern part was modeled. The cut was performed at the upper boundary of glaciofluvial deposits and where the sediment thickness starts to increase. The calculated flux from the cut area due to recharge associated with precipitation, was distributed to the western border. The flux was assigned with more strength at the northern part, because of the greater amount of water ending to it. Although the water table measurements were limited, the model was calibrated, using them. The model was run with and without the present pumping at the waterworks. Furthermore, different scenarios were tested on the model, including increased pumping rate and possible flux entering from the northern boundary of the catchment. The results showed that during the extraction of groundwater there is a significant amount of recharge from the river Glomma. This result needs further investigation. Furthermore, the results of the scenario with the flux from the north, showed similarities with the final calibrated model. Thus, it is concluded that there is flux from the northern boundary is rather small. Hence, more piezometric data are needed to quantify this potential flux. The results from the water chemistry showed a problematic analysis with increased error in the electrical balance. Nevertheless, the ICP-MS analysis for iron and manganese showed that the groundwater after the treatment with the Vyredox method is safe for consumption.