The rehabilitation of ancient gas factory sites

In France, the inheritance of ancient town gas factories, mainly under the responsibility of Gaz de France, has left pollutants in the soils of their sites. The aim of the national company is to control these pollutants. Several hundred of town gas factories were exploited in France from 1798 (date of the invention of the process by Lebon) to the end of the 60's. The town gas, obtained from high temperature pyrogenic decomposition of coal, led to by-products which were stored or mixed with the soil. This paper describes the environmental and quality policy carried out by Gaz de France to characterize and remove the pollutants (coke, clinker, tar, phenols, ammoniated water, hydrogen sulphide, cyanides, benzene, toluene, xylenes..) to evaluate the risks of exposure of contaminants and their possible impact on human health. A method with 17 criteria was elaborated to characterize the sites and the rehabilitation comprises three steps: the environmental audit (evaluation of the concentration of pollutants and of their possible environmental and human impact), the complementary analysis (extension of the contaminated area, nature and concentration of pollutants, geologic and hydrogeologic characterisation of the site), and the rehabilitation itself when necessary (confinement or elimination of pollutants using thermal, physico-chemical or biological treatments). (J.S.)