GIS Techniques for Mapping Groundwater Contamination Risk

Abstract

The groundwater contamination risk map of a sample alluvial area was produced by using the Ilwis Geographical Information System (GIS) to construct and to overlay thematic maps. The risk map has been derived from the vulnerability map, the hazard map, where the potential contaminating sources were identified, and the socio-economic value of the groundwater resource, represented by the wells. The groundwater quality map allowed the reliability of hazard and risk maps to be tested. The final map shows interesting results and stresses the need for the GIS to test and improve on the groundwater contamination risk assessment methods. The Environmental Protection Agency, in the United States, has identified in 1993 more than 200 chemical compounds in groundwater (EPA, 1993), some of these are extremely hazardous to human health. Pollutants reach the aquifers from ordinary human activities (agriculture, farming, industry) or from occasional sources. In consequence the groundwater protection is a prior environmental concern in many countries, for example in Europe, where more than 50% of the water supply is obtained from groundwater (Lobo-Ferreira, 1997). The correct way to solve this problem is to prevent the contamination assessing and managing the groundwater pollution risk at regional scale. In this paper the groundwater contamination risk map of a sample alluvial area was produced by using the Ilwis Geographical Information System to construct and overlay thematic maps. The adopted groundwater contamination risk assess- ment method follows the approach of previous studies published in Italy (Civita, 1995; Civita and De Maio, 1997; Corniello and Ducci, 1997) and is optimised by developing new analytical procedures. Moreover, the use of the GIS has allowed: high spatial resolution; numeric checking of calculated parameters and easy matrix operations.