Vulnerability mapping is used for groundwater protection planning, management and decision making, for the identification of areas susceptible to contamination and for public information and education. Groundwater vulnerability assessment is an important basis to fulfill with the European Union Water Framework Directive (EU_WFD) 2000/60/EC. The Portuguese law (D.L. 382/99; L. 58/2005; P. 702/2009) establishes that wellhead protection areas are defined considering the hydrogeological conditions and encompasses 3 protection zones: an immediate zone, usually marked by a fence, where all activities not linked to groundwater exploitation are forbidden; an intermediate zone, where all activities that may contaminate the groundwater, whether by the infiltration of contaminants or by changing the flow paths, are forbidden or at least strictly controlled; an extended zone, where the constraints to activities are still applied but in a less severe way. A vulnerability-based approach for delineating groundwater protection zones around springs in fractured media may be developed with several methods, namely the DISCO index. DISCO index is normally applied in case of vulnerable springs linked to a highly heterogeneous aquifer and includes the characterization of the hydrogeological properties of the aquifer (DIScontinuities parameter) and the thickness and permeability evaluation of the protective cover (protective COver parameter).
This work aims to propose the delineation of protection zones of the main discharge area of a granitic system located in an urban area of NW Portugal. The main spring constitutes one of the most important groundwater resources of the area and its flow rate displays a strong annual variability in the range 35-70 m3/day. The interest for this area is related to its availability of groundwater resources, to contamination issues and to the recovery of the old water system of natural waters for the water supply to the main gardens and fountains. To fulfill this goal, and taking advantage of a GIS (Geographic Information System)-based mapping, interactive geo-databases were created to organise and analyse all the data, namely: topography, land use/land cover, geology, morphotectonics, hydrogeology, climatology, urban hydraulics and sanitation, as well as an inventory of surface and shallow groundwater potential contamination activities. Moreover, several groundwater vulnerability maps were outlined recurring to GOD, DRASTIC-Fm, SINTACS, SI and DISCO indexes.
This study may be integrated as a tool in an urban territorial planning for a sustainable development.