A new challenge in urban management is nowadays represented by the remediation of large contaminated industrial facilities. Different examples of these industrial sites are widespread in the European territory, from the Netherlands  (e.g. the Port of Rotterdam) to Germany (the mining site of Bitterfeld) and the Eastern countries (e.g. the  Tarnowskie Gory plant site in Poland). These sites, defined as megasites, are characterized by complex contamination patterns, several stakeholders' involvement and high costs for total clean-up procedures. Their relevance is posed by the social, economic and also environmental benefits derived by their remediation and their new economic development.
Therefore, the definition of specific tools and strategies, that can help manage megasites complexity, is required. Specifically, the integration of all the different management aspects is a primary requirement: the consideration of the actual risk, the selection of the best technological options for site remediation, the socio-economic drivers or constraints, the planning issues, are among the significant aspects which are to be strongly taken into consideration. Equally, the active involvement of all the stakeholders in the decision process is another important requisite in order to successfully accomplish management objectives.

In this communication we present the experience gathered in the management of the Porto Marghera site, through the development of a decision support system called DESYRE. Porto Marghera, near the city of Venice in Italy, is the largest contaminated site of national interest (approximately 3500 hectares). The main productions are represented by petrochemical and chemical plants; spread contamination affects soil and groundwater.

The regulatory framework is represented by the Program Agreement on Chemistry (1998), signed by several stakeholders, and the Master Plan (2001), based on a risk minimization approach. In order to address the management of a complex megasite such as Porto Marghera, the DSS DESYRE (DEcision Support sYstem for REhabilitation of contaminated sites) has been developed. In fact, it has been successfully tested in two areas of the Porto Marghera site. DESYRE is a GIS-based software composed of five interconnected modules.

In the characterisation module, chemical and hydrogeological data are organized in a relational database and contaminants distributions are mapped by using geostatistic tools.

1. The socio-economic module addresses the socio-economical constraints though a Fuzzy Logic analysis, until the selection of the best land use.
2. The risk assessment module is divided into two phases. In the pre-remediation phase, an original procedure allows to assess and represent the spatial distribution of risks posed by contaminants in soil and groundwater, providing a risk-based zoning of the site.
3. Then, in the technology assessment module, a selection of suitable technologies and the creation of different technology sets, taking into account both technical requirements and site-specific features, is performed by experts supported by Multi-Criteria Decision Analysis tools. In the post-remediation risk assessment, a simulation of applied technologies provides residual risk maps with related uncertainty maps.
4. Finally, in the decision module, alternative remediation scenarios are described by a set of indices; the scenarios can be compared and ranked by the interested stakeholders using Multi-Criteria Decision Analysis methodologies.