Assessment of groundwater quantitative status: implementation on the Aosta Plain aquifer

The EU Water Framework Directive (WFD; 2000/60/EC) and the Groundwater Directive (GWD; 2006/118/EC) established a framework for Community action in the field of water policy. In particular, the WFD requires the fulfilment of a good both qualitative and quantitative status of groundwater. The national regulation integrating the WFD in Italy (D.Lgs. 30/09) does not provide precise indications about the quantitative classification of groundwater bodies. In order to fill this regulatory gap, a recent guideline based on the WFD was developed by the Italian Institute for Environmental Protection and Research (ISPRA) aimed to assess the groundwater quantitative status. The guideline provides the workflow for a standardized large-scale assessment of the quantitative status of groundwater. The guideline’s workflow is articulated in four tests: 1) water balance, 2) surface water, 3) groundwater dependent terrestrial ecosystems and 4) salt intrusion. In this work, the proposed methodology by ISPRA was applied on the Aosta Plain alluvial aquifer (northwestern Italian Alps) monitored since 2003 from the local Environmental Protection Agency, in order to evaluate its effectiveness and practicality in a real case study. Using piezometric and abstraction data and their processing through a numerical groundwater flow model, the test 1 was applied through its related three phases: 1) preselection, 2) groundwater level trend assessment and 3) water balance. Hydraulic head time series for 64 piezometers were analyzed, however only 5-10 of these would have a sufficient record of measurement result as required by the ISPRA guidelines. Moreover, critical issues emerged as regard to 1) hydrogeological data availability and 2) the sampling frequency. In particular, long-time (~16 years) hydraulic head time-series resulted more reliable than the shorter one (at least 2-3 years), while sampling frequency seems less important on the assessment of the groundwater quantitative status, although a minimum of two measurements per year are required. Results clearly show that the quantitative status in the study area must be considered so far “good”. However, climatic changes may modify significantly the current conditions in the next years, obliging to maintain a high attention toward the quantitative status monitoring.