Interrelation of wastewater and groundwater management in the city of Bijeljina in Bosnia

The city of Bijeljina lies on alluvial deposits of the river Drina, which provide groundwater storage of great capacity with good hydraulic properties. Groundwater is abstracted by wells which are located in a field close to the city, and used for public water supply. In the summer of 1993, large numbers of coliform bacteria were found repeatedly in two of the wells. A study was initiated with the main objective of providing a short-term solution to the problem, as well as some guidelines for the long-term groundwater management strategy. A regional groundwater flow model was developed, calibrated and verified. In situ tracer experiments were used to improve the reliability of particle tracking computations. The results were used to prove that the sources of pollution were domestic septic tanks upstream of the well field. The problem was temporarily solved by closure of five wells capturing polluted water and opening some new wells in the less affected zone. The particle tracking results show why this strategy works, but also show that it is only a temporary solution. As a long-term solution, a sewerage system and network of monitoring wells were proposed. The sewerage system has been constructed recently. The role of monitoring is to check if bacterial pollution has ceased following the construction of the sewerage system, as well as to detect other types of pollutants. Groundwater levels have been monitored for one year already, so the data for model re-calibration has been collected. The re-calibrated model can be used for more accurate delineation of protective zones, prediction of the risks related to other pollutants, analysis of the possibility to reactivate the closed wells, etc. As the major objective in long-term water resources management, it is proposed that an integrated approach should be adopted, with simultaneous management of water supply, wastewater and solid waste.