The influence of organic contamination of surface water in the Morava river (Czech Republic) on groundwater quality in its floodplain

The relation between water in the stream and shallow alluvial groundwater was studied between 1991 and 1995 on the right bank floodplain of the Morava river between release canal (Nova Morava), Moravsky Pisek and Veseli nad Moravou. By means of manipulation with weir flap at Uhersky Ostroh and Vnorovy at this artifical canal, it is possible to reach the long-term increase of water level in a canal of more than 3.5 m and simultaneously bank infiltration to the permeable alluvial sediments. Results of groundwater chemical analyses from various objects confirmed the original assumption, that organic contaminating substances are getting into shallow groundwater of the floodplain by bank infiltration of contaminated surface water from the Morava river and this release canal. This reality is obvious especially from concentration values of organic matter in water from observation well HV 112/2 (150 m from canal) and from the more distant well HV 112 (380 m from canal). Comparing complete content of PCB, HCH, HCB and DDT we can find that in all cases concentration values in groundwater from HV 112 are lower than from HV 112/2. Analyses of the river sediment samples confirmed that lipophylic organic contaminants are absorbed in them. Analyses proved presence of congeners of PCBs in those sediments. There are present also hexachlorhexans, hexachlorbenzen, DDT and another chlorinated pesticides. As well as in the case of analysed water and sediment samples from the Morava river are more contaminated than those from the canal. From results of analyses of river sediments it follows that surface water which via bank infiltration gets into permeable sand and gravel sediments of the floodplain can worsen pollution of shallow groundwater. Main influences which can take part in transportation of organic compounds from river sediments into groundwater in adjacent territory are physical and chemical properties of these compounds, intensity of bank infiltration, petrographical characteristics of permeable rocks, and hydraulic conductivity between these water bodies