GROUPInG OF GROUnDWATER MOnITORInG POInTS In RIVER FLOODPLAIn ACCORDInG TO THE COnDITIOnS FOR ARSEnIC COnTAMInATIOn

The purpose of this study is to categorise 21 groundwater monitoring points in the mining-affected valley of the Ogosta River in northwestern Bulgaria according to the conditions for arsenic contamination of the alluvial aquifer. The grouping of the sites has been performed based on geochemical and geographical indicators using cluster analysis. Representative monitoring wells have been selected from each group so as to optimise the monitoring program and reduce the related expenditures. An attempt has been made to link the categories of piezometers to the main geomorphological features of the river floodplain and to certain levels of arsenic pollution of groundwater. The revealed patterns can be used for further examination of the link between arsenic dynamics and the geographical settings of the river floodplain. The established relationships are relevant to the environmental settings of a mountainous river of medium size under temperate climate conditions.