eNaBLe, an On-Line Tool to Evaluate Natural Background Levels in Groundwater Bodies

Inorganic compounds in groundwater may derive from both natural processes and anthro-pogenic activities. The assessment of natural background levels (NBLs) is often useful to distinguishthese sources. The approaches for the NBLs assessment can be classified as geochemical (e.g., thewell-known pre-selection method) or statistical, the latter involving the application of statisticalprocedures to separate natural and anthropogenic populations. National Guidelines for the NBLsassessment in groundwater have been published in Italy (ISPRA 155/2017), based mainly on thepre-selection method. The Guidelines propose different assessment paths according to the samplesize in spatial/temporal dimension and the type of the distribution of the pre-selected dataset, takingalso into account the redox conditions of the groundwater body. The obtained NBLs are labelled witha different confidence level in function of number of total observations/monitoring sites, extensionof groundwater body and aquifer type (confined or unconfined). To support the implementationof the Guidelines, the on-line tool evaluation of natural background levels (eNaBLe), written inPHP and using MySQL as DBMS (DataBase Management System), has been developed. The maingoal of this paper is to describe the functioning of eNaBLe and test the tool on a case study incentral Italy. We calculated the NBLs of As, F, Fe and Mn in the southern portion of the MountsVulsini groundwater body, within the volcanic province of Latium (Central Italy), also separating thereducing and oxidizing facies. Specific results aside, this study allowed to verify the functioning andpossible improvements of the online tool and to identify some criticalities in the procedure NBLsassessment at the groundwater body scale