Wellfields under heavy urban pressure-monitoring, simulation, maintenance

Abstract

Drinking water supply in Lithuania is entirely based on groundwater. Vilnius, Capital of Lithuania, is no exception. One of the oldest wellfields of the City, operated since 1956 and named ‘Vingis’, is located in industrial area of Vilnius and surrounded by various groundwater contamination sources. The nearest groundwater contamination site was and is an abandoned huge plant ‘Velga’, which in Soviet time contained large storages of industrial solvents (VOCs) of PCE, TCE-type. Groundwater abstraction activated VOCs migration into wellfield, highest concentrations of two main VOCs (PCE and TCE) in some pumping wells of this wellfield often and significantly exceed drinking water standard (10 ?g/L) and even the limit, recommended by WHO (110 ?g/L). In spite the fact, that groundwater polluter lies nearby, only traces of VOCs were detected on its territory. Subsequent studies revealed the ‘secret’: heavy, poorly soluble VOCs have migrated from the territory of the polluter and have accumulated in the lowermost places of pumped aquifer, detected inside the wellfield. Finally, an acceptable concentration of VOCs in supplied drinking water was ensured by permanent pumping out of the most polluted groundwater from some abstraction wells of the wellfield and diverting this water to the river. An effective tool of groundwater resources management is our 3-D model of Vilnius Metropolis, permanently supplied by new groundwater monitoring data. This model was also successfully used for pumped aquifers vulnerability assessment and delineation of groundwater protection zones.