A methodology for spatial and temporal classification of groundwater quality

industrial wastes and of substances used in agriculture, is a matter for studies of researchers involved on problems related to the management of such resources. This is the reason why several laws have been produced to protect groundwato: They state its importance as a source for drinkable suppl)~ underline its vulnerability to the loads and define the standards of quality for civil use and, particularl)~ for potable supply (DPR 236/88, L. 36/94, DL 152/99). Therefore, it is of remarkable interest, above allfor the authorities provost to the territorial planning, to have schematic tools that characterize groundwater in terms of quality and quantity. In this paper a classification based on a noted methodology defined by the Water Research Institute of the Italian National Research Council (IRSA-CNR) and National Group for the Defense from Hydrologic Catastrophes (GNDCI) for the representation of the baseline groundll'ater quality is applied. This methodology is based on the elaboration of the concentration mlues of several among the most important pollutants and chemical and physical parameters that are typical of the natural hydrochemical water conditions and/or representative of possible man induced modifications on the aquifer. The substantial difference bel1veen the methodology used in this paper and that one of the GNDCI consists of the grouping of several of the nine final classes of quality, reduced to five, with a consequent simplification of the resulting maps. The simplified methodology of classification has been already applied to the aquifer of the plain of Lucca (central Italy). However, the applications peiformed up today have generally considered data of single monitoring campaigns, limiting themselves to a static representation of the qualitative state of the groundwater. The resulting maps, although representative of the quality, do /lot contain any information on its evolution. To appraise the possibility of improving the representation of the qualitative state of the aquifel; considering its temporal dynamics, a methodology has been applied to data of a series of monitoring campaigns, pelformed in spring and autumn from 1990 to 1996 in the aquifer of the plain of Modena (central Italy). The result is represented by Cl chronological succession of maps of qualit}; a sort of storyboard, that describes its variation in time and that allows to base managerial choices not only on the knowledge of spatial information but, also, on the evaluation ofthe temporal evolution of the water quality