Abstract :
[en] In the Walloon region of Belgium, as in many other countries, approximately 80% of drinking water supply is provided by groundwater catchments. Many of these catchments are located in rural areas and most often threatened or impacted by pollutants of agricultural origin, such as nitrate and pesticides. However, a significant proportion of groundwater catchments are located in peri-urban environments surrounded by residential, industrial, economical areas where many different types of sources of point and diffuse pollution coexist, such as accidental spills, continuous, hidden leaks in drainage networks, old dumps, treated and untreated wastewater or watercourses.
In this context, the CASPER project financed by SPGE has focused on the development of an integrated methodology for the protection and management of groundwater catchments in such peri-urban catchments in order to manage the problem of water quality, distinguishing between various possible sources of contamination and possible mixtures between different types of water and pollution sources. The CASPER methodology is based on few basis concepts. First, the methodology is applied specifically to the groundwater catchment area which corresponds to the land surface perimeter in which abstracted groundwater is recharged, either by direct infiltration or by lateral runoff first and subsequent infiltration. In a second step, a groundwater monitoring network is established, and groundwater sampling organized focusing on a set of indicators of different types of pollution sources. It combines the use of physicochemical parameters and traditional hydrochemicals and more advanced hydrochemical indicators. In particular, stable isotopes of NO3- and boron are used to distinguish between inputs linked to urban effluents and agricultural fertilisers. The occurrence of specific molecules such as pharmaceutical and lifestyle products are used as effective tracers of anthropogenic contamination. Microbiological analyses are also included to identify microbial populations associated with specific sources of pollution or certain biochemical reactions occurring in soil and groundwater. This very detailed dataset is finally used to discriminate between different sources of pollution based on multivariate analyses and clustering. The third step of the approach consists in evaluating the strength of the different pollution sources identified in the catchment area based on in situ measurement and modelling of pollutant mass fluxes and mass discharge, in order to prioritize remediation measures on the most intense sources of pollution.
This newly developed approach has been tested using the groundwater catchment site of Boussu in the province of Hainaut (western Belgium) as a first pilot case study. It is located in a peri-urban area impacted by various sources of pollutants coming from old dumps and slag heaps which surround the site, railway wastes, discharges from small and medium-sized enterprises, hospitals, housing and possibly agriculture.
