During the next decade changes are expected in the western area of the active part of the Estonia oil shale deposit since Ojamaa mine started to dewater the oil shale layer and environmental impact assessment is in the process of estimating the influence of dewatering on the site of Uus-Kiviõli mine. Aidu open cast is planned to close down in 2013 as the resources of oil shale indicated in the mine permission are ending. Closing of Viru mine in 2015 has been discussed. As the oil shale resources at Aidu and Viru area end, the mine sites will be closed and flooded. Therefore the groundwater table will increase in closed sites and will decrease in prospective areas. To estimate and visualise the situation, computational modeling of groundwater flow has been applied in most cases to estimate the future situation. The current analysis describes the process of groundwater modelling as well as offers possibilities of estimating the accuracy of the model and of the model calibration process. Water inflow rate into Estonia mine has been analysed.

The present paper is based on the results of the research conducted in 2004 by the Department of Mining of the Tallinn University of Technology and Estonian Oil Shale Company. The state of the technogenic water body that has formed in the central part of the oil shale deposit is analysed: the water level in the area of the stopped and closed mines, water amount and movement direction, water quality and its changes. The state of the water is assessed and predicted using modelling of the water tables, statistical analysis of the water quality parameters and the pilot model for describing the migration of water. The results show that the technogenic water body studied is in a relatively stable state, and the quality of the groundwater in that area is fast improving approaching the drinking water standards.