Land application of sewage and sewage sludge, incorrect draining off of wastewater, and also accidents, can lead to contamination of groundwater with pathogenic and facultative pathogenic micro-organisms. If no inactivation or elimination of such contaminants takes place, the hygienic quality of groundwater can be negatively affected. In model experiments carried out in the laboratory, the survival of Escherichiacoli, Salmonellatyphimurium, Yersiniaenterocolitica, Pseudomonasaeruginosa, Staphylococcusaureus, StreptococcusfaecalisBacilluscereus, Bacillusmegaterium, Clostridiumperfringens, Aspergillusniger, Nocardiaalba and Streptomycesgriseus in groundwater kept at 10°C was tested. Although no apparent proliferation of the micro-organisms was observed during the experiments, most of them survived for an extended period up to 300 days. Only B.megaterium and S.aureus were not detectable after 12 and 30 days, respectively. Sand originating from a groundwater aquifer, and also the enrichment of the groundwater with humic acid and potassium nitrate as sources of carbon and nitrogen did not affect microbial survival substantially. Adhesion of micro-organisms to sand was observed, which may influence both the persistence and transportation of micro-organisms in the aquifer. The results of these experiments can be of importance for determining groundwater protection zones.

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