Environmental sciences are evolving from a simple, local-scale approach toward complex multilayered, spatially explicit regional endeavours. Advances in computer simulation and high performance computing in recent years greatly extends the possibilities in this field, and changes the ways in which land management systems operate. The Datacrossing DSS is decision support system that relies on a basin-scale groundwater model and a geographically distributed GIS to support decision makers, through a user-friendly Web interface, in the field of sustainable water resources management. The portal, for the general user, exposes hydrological applications based on geochemical field data, geophysical surveys, and results of the finite element hydrological CODESA 3D model to quantify the impact of point/non-point pollution. Within an experimental collaborative environment, modules have been developed to run real-time applications based on numerical solvers, run pre- and post-processing codes, query and map results through the web browser. Our aim is to build a collaborative platform that, by introducing the computational and data-sharing advantages of a GRID infrastructure, promotes joint initiatives and encourages cooperation among interdisciplinary teams operating in the environmental sciences. To illustrate the potentiality of our decision support system, we present its application to a complex industrial area in Sardinia, Italy (the Portoscuso site) and a less impacted aquifer in Morocco, province of Tétuan (the Oued aquifer)