Drying up of a natural spring for ensuring stability of an artificial slope: is it sustainable development ?

Near a small city of the Belgian ‘Ardennes’ (East of Belgium), modification of a natural slope for extension of industrial activities has required an extensive drainage in a weathered zone composed of colluvium and weathered claystones and quartzites. After a few days, the drain at the foot of the artificial slope was producing about 1000 m3/day while a natural spring located at a 200 m distance on the hillside was completely dried up. This spring was used for drinking water by the local community. A shallow geophysical prospection by refraction seismics and 2D geoelectrical tomography, associated to geological, morphostructural and hydrogeological observations have lead to a clear understanding of (1) the spring occurrence; (2) the feeding conditions of the spring and consequently (3) the ‘lateral’ hydraulic impact of the drain. In the hill, the bedrock is changing from quartzites (uphill) to claystones (downhill) inducing changes in hydraulic conductivity and thickness of the overlying weathered zone. On the basis of these hydrogeological conditions, associated to the specific topographic conditions, different possible remediation schemas have been proposed to the decision makers. Unfortunately, the full restoration of the natural spring appears to be one of the most technically and financially difficult option …while it is surely the most suitable in the name of a sustainable development.