BARIUM ANOMALY IN THE CAMBRIAN-VENDIAN AQUIFER SYSTEM IN NORTH ESTONIA

Abstract

A barium anomaly with a maximum Ba2+ concentration of 6.37mg/l was distinguished in a Cambrian-Vendian (Cm-V) aquifer system that is widely used as a drinking water source in the towns Kunda, Rakvere and Kohtla-Jrve of North-Estonia. The modelling results show that at low sulphate concentrations (below 3mg/l) Ba2+ contents can exceed the limit values for drinking water (such as 2mg/l set by US EPA). Bicarbonate ions in their common concentration range in groundwater cannot limit Ba2+ at its content below 10mg/l. The probable natural sources of the anomaly are the crystalline basement and its weathering zone. Groundwater in the clayey weathering core is hydraulically connected with the overlying Cm-V aquifer system, thus the upconing of deeper-seated groundwater, caused by intensive exploitation of wells, is possible.