The influence of polluted water flows on hydrological and hydrochemical conditions of Purtse catchment rivers, NE Estonia - Paper presented at the Nordic Hydrological Conference (Uppsala, Sweden June, 2000)

The correlation between natural (meteorological, hydrological), mining-tech nological, hydrogeological and geochemical factors in the oil shale mining region in the Purtse catchment area for the period of 1990-1998 was studied . As a result of the interactions between these factors (correlation coeffi cients r=0.56-0.86), a so-called hydrogeological circulation of water has f ormed in the catchment area. It was found that the circulation flow forms 2 5-40% of the total amount of mine water pumped out from the mines at presen t. On the basis of average data, a new balance scheme of water circulation (cycles) for the Purtse catchment was developed. Under the influence of dif ferent water flows a new, anthropogenic biogeochemical matter cycling from the geological environment into the aquatic environment of the rivers has f ormed in this catchment area. The pollution of the Purtse River from oil sh ale thermal processing is combined with the harmful impact of oil shale min ing. The anthropogenic hydrochemical conditions arising in the rivers of th is catchment will not disappear even after oil shale mining stops. A multip le regression formula was derived for prognosticating the flow regime (mean annual discharge) of the Purtse River using meteorological and mining-tech nological data.