The present EIA was not preceded by the elaboration of a Scope Definition Proposal (PDA), under the terms of Decree-Law No. 197 /2005, of November 8. However, in its planning, organization and definition of work methodologies, the environmental aspects considered most relevant or most sensitive for the analysis of Ah do Alvito's preliminary project were immediately identified. Thus, a hierarchy of the descriptors analyzed in the present study was established based on a preliminary assessment of existing natural and socio-economic values in the study area and on the integrated analysis of the various basic studies of the preliminary project