SURVIVAL, TRANSPORT AND DISSEMINATION OF ESCHERICHIA-COLI AND ENTEROCOCCI IN A FISSURED ENVIRONMENT - STUDY OF A FLOOD IN A KARSTIC AQUIFER

In fissured aquifers, hydrodynamic phenomena combined with a network o f permeable fissures imparts varying degrees of vulnerability dependin g on the type of contaminant. The study presented here examines the im pact on a karst aquifer of a river which receives effluents from a sew age treatment plant just upstream from the point of recharge. This rec harge constitutes a source of bacteriological and chemical pollution. The aquifer is accessible by boreholes at discrete points, facilitatin g investigation of the evolution of three of the contaminants characte ristic of treatment station effluents, NH4+ and two biological contami nants with different survival capacities. The study was undertaken bot h under normal climatic conditions and during a flood occurring after a long dry period. The rate of infiltration, of subsurface transport, and of dissemination of contaminants into a zone usually protected fro m contamination was recorded. The results confirm the vulnerability of fissured aquifers to contamination.