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-technological, 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 coefficients r=0.56-0.86), a so-called hydrogeological circulation of water has formed in the catchment area. It was found that the circulation flow forms 25-40% of the total amount of mine water pumped out from the mines at present. On the basis of average data, a new balance scheme of water circulation (cycles) for the Purtse catchment was developed. Under the influence of different water flows a new, anthropogenic biogeochemical matter cycling from the geological environment into the aquatic environment of the rivers has formed in this catchment area. The pollution of the Purtse River from oil shale thermal processing is combined with the harmful impact of oil shale mining. The anthropogenic hydrochemical conditions arising in the rivers of this catchment will not disappear even after oil shale mining stops. A multiple regression formula was derived for prognosticating the flow regime (mean annual discharge) of the Purtse River using meteorological and miningtechnological data.