Groundwater is an important component of many water resource systems supplying water for domestic use, industry, and agriculture. Management of a groundwater system, an aquifer, means making such decisions as annual withdrawal of the total quantity of water, location of wells for pumping and for artificial recharge and their rates, and control conditions at aquifer boundaries. The decisions related to groundwater quality are of no less importance. In fact, the quantity and quality problems cannot be separated. In many parts of the country, with the increased withdrawal of groundwater, the quality of groundwater has been continuously deteriorating. In recent years the attention has been focused on groundwater contamination by mine water. A thorough understanding of the system, and the processes that take place in it are needed for modeling procedure. It is important to identify those parts of the system's behavior that are relevant to the considered problem, while other parts may be neglected. On the basis of this understanding, summarized as a conceptual model of the given problem, a numerical model was constructed. Using the conceptual model the groundwater flow model of the Quaternary aquifer, in the eastern part of oil shale deposit area, in the Vasavere buried valley, was constructed. The infiltration of contaminants grows, and the Quaternary aquifer is polluted by sulphate in a large area of the Vasavere buried valley.