Présentations Colloques

Oral Presentation
Session 7.02: Urban Hydrogeology
Seidl Martin
Seepage water. A new resource?
The city of Paris was constructed on the banks of the river Seine approximately in the center of its river basin, made of marine sedimentary rocks like limestone and gypsum. The presence of rivers, combined with precipitation and permeable underground has as consequence that numerous underground infrastructures like subway, parkings or basements of modern building complexes are submerged in ground water and have to deal with seepage water. Paris is therefore pumping about 20 000 cubic meters daily to keep its underground infrastructure dry. This water is discard principally into the combined sewers of the city and charged for collection and treatment. Paris is also using a huge amount of river water for urban uses like sewer flushing, street cleaning and watering. The seepage water could potentially be used for these city needs preserving rivers for other needs. Though the elevated hardness and conductivity of seepage water together with long residence times in the secondary supply network and the quality needs for lane watering, make the equation less simple. **To evaluate adequately the potential of seepage water utilization, better knowledge of existing resources and application risks is needed. The proposition will give a quantitative and qualitative estimation of seepage water at present and sketch the limits of its application. A GIS is used to link existing seepage water data with geological and hydrological information to test the relation with the underground composition and the presence of urban rivers. The presentation will complete this picture with case studies where partial use is practiced and their simplified cost – benefit balance. Preliminary results indicate that seepage water might contribute to the reduction of the environmental impact of the existing city water cycle if appropriate changes are made to the actual water practices.**