CRA-W's committee of intervention: analyse of catchments polluted with pesticides

In the Walloon Region of Belgium, a committee of intervention has been created to investigate problems of pesticide contamination of various catchments use for drinking water production. This committee involves the Agricultural Research centre--Wallonia (CRA-W, project coordinator) and some University experts. It is funded by the Société Publique de Gestion des Eaux (SPGE). The diagnosis method, base on the AQUAPLAINE method (Arvatis-France), consists of 4 steps. The first step is the preparation of diagnosis (at the office) that takes into account the paper risk of active ingredients. and their uses, the identification of the agricultural parcels, the collection of cartographic and numeric data, the description of the hydrogeological and pedological contexts and the study of the meteorological data in relation with the period of pollution. The second step consists of making a plot diagnosis (on the field) to identify the way of transfer inside the plot and collecting data. At the third step, the people who can apply PPP treatment close to the catchment are met (farmers and city services). Information are collected on treatments applied and on the state of parcels. Based on the hypothesis of pollution cause, the committee proposes solution to solve the problem. One of the catchment that has been investigated by the committee is located at Biesmerée, (Namur province, in Belgium). A temporally contamination was caused by 4 pesticides : chlortoluron, isoproturon, trifluralin and diflufenican. After investigations, it seems that the pollution was probably due to the hydrogeological context. As the river is locally perched over the aquifer, the presence of Poly-aromatic hydrocarbons (PAHs) could be due to the infiltration of surface water inside the catchment or/and to the presence of a sinkhole temporally activated during river flood period. Infiltration rate has to be assessed and river bank impermeabilization is recommended.