Groundwater hydrodynamic behaviours based on water table levels to identify natural and anthropic controlling factors in the Piedmont Plain (Italy)

Perfluoroalkyl substances (PFASs) in groundwater and surface water in the Turin metropolitan area (Italy): An attempt to unravel potential point sources and compliance with environmental/drinking water quality standards

The study investigated the contribution of five potential point source categories on the occurrence of 19 highly hazardous perfluoroalkyl substances (PFASs) in freshwater from the Turin metropolitan area (Italy) and assessed the quality of groundwater and surface water in compliance with European and Italian guidelines. PFASs were revealed in 29 and 24 % of the investigated shallow (unconfined aquifers) and deep (semi- and confined aquifers) wells with a total concentration, as a sum (ΣPFASs), of 0.01-0.71 and 0.01-0.16 μg/L, respectively. The PFAS occurrence in shallow groundwaters appeared more related to (potentially-) contaminated and reclaimed areas, landfills and waste management plants rather than plants subjected to integrated environmental authorisations and wastewater treatment plants. Overall, PFAS occurrences increased with the degree of industrialisation and urbanisation in both unconfined and (semi-) confined aquifers. PFASs were found in 96 % of the sampling sites in streams with ΣPFASs values of 0.0002-0.47 μg/L, whilst they do not occur in the investigated lake. A slight correlation was found between wastewater treatment plants and the occurrence of PFASs in streams. The annual ΣPFASs loads downstream of the Turin metropolitan Area were estimated around 150-220 kg. Exceedances of the environmental and drinking water quality standards of Italy and Europe were frequently revealed.

Application and comparison of different statistical methods for the analysis of groundwater levels over time: Response to rainfall and resource evolution in the Piedmont Plain (NW Italy)

Monitoring and analysis of groundwater level (GWL) in space and time is one of the tools used to evaluate the quantitative status of groundwater (GW) resources and identify possible alterations and critical cases due to climate change and variability, anthropogenic influences and other driving factors. In this study, four statistical methodologies (trend, change-point, percentile and non-standardized anomaly analyses) were applied for GWL and rainfall (R) analysis in the Piedmont Plain (western Po Plain, NW Italy). To detect the interannual variations in the GW maximum annual amplitude, the coefficient of variation was also used. The aims of the study were 1) to compare the results of different statistical methods, highlighting their applicability and differences to evaluate the quantitative evolution of GW, 2) to identify the relationship between GWL and R, 3) to investigate the spatiotemporal variation in the GWL of shallow aquifers in the Piedmont Plain, and 4) to describe critical situations of GW depletion. The study highlights that the application of a single method for assessing the shallow GW resource status does not always guarantee a reliable evaluation. For this reason, it is advisable to apply different analysis methods at the same time. Completeness of data and medium to long time series are prerequisites for meaningful analyses. The use of the same time interval is always necessary for comparisons between different monitoring wells and between the results of different statistical analyses. Last, by spatializing the results, it was possible to identify areas characterized by similar GWL behaviour due to hydrological structure, climate variability, land use and the evolution of anthropogenic activities over time. These factors influence vary locally in the Piedmont plain and require local assessments to determine the impact of changes in GWL.

Temperature and discharge variations in natural mineral water springs due to climate variability: a case study in the Piedmont Alps (NW Italy)

In the context of global climate change, understanding the relationships between climate and groundwater is increasingly important. This study in the NW Alps represents the first regional-scale investigation of the groundwater feature variation in mountain aquifers due to climate variability. The analysis of groundwater temperature and discharge in 28 natural mineral water springs and meteorological parameters (rainfall and air temperature) permitted us to evaluate the annual behaviour and possible trends of these parameters during the period from 2001 to 2018. The air temperature showed a positive trend almost everywhere, with a rise of up to 0.03 °C/year. In contrast, only ten springs showed a positive trend for groundwater temperature, but with the smallest rates of increase. Moreover, despite the substantial stability of the rainfall amount, 50% of the analysed springs showed a trend (29 and 21% for positive and negative trends, respectively) with low discharge variations. Finally, cross-correlation analyses proved the close relationship between air and groundwater temperatures, with a time lag between 0 and 3 months, and between spring discharge and air temperature, with a time lag between 1 and 3 months. In particular, spring discharge is closely connected to snow melting in spring and subordinate to rainfall. These results highlight the existing correlations between spring discharge and various meteorological and topographic parameters in the studied mountain area and provide a preliminary framework of the impacts of climatic variability on the availability and temperature of the exploited water resources.

Trends in Groundwater Levels in Alluvial Aquifers of the Murray–Darling Basin and Their Attributions

Groundwater levels represent the aggregation of different hydrological processes acting at multiple spatial and temporal scales within aquifer systems. Analyzing trends in groundwater levels is therefore essential to quantify available groundwater resources for beneficial use, and to devise plans/policies to better manage these resources. In this work, three trend analysis methods are employed to detect long-term (1971–2021) trends in annual mean/minimum/maximum depth to water table (DTW) at 910 bores. This analysis is performed in eight main alluvial systems in the Murray–Darling Basin (MDB), Australia, which concentrate nearly 75% of groundwater use. The results show: (a) an overall increasing trend in DTW across alluvial aquifers attributable to changes in recharge from rainfall and groundwater extraction; (b) the analysis methods employed show similar statistical significances and magnitudes, but differences exist; (c) the annual minimum DTW has a smaller trend magnitude than annual mean DTW, and the annual maximum DTW has a larger trend magnitude than mean DTW; (d) trends in annual rainfall and potential evaporation, and cumulative number of production bores, are consistent with the groundwater trends; (e) irrigation is responsible for some of the decreasing trend in groundwater level. These results could be used to target further research and monitoring programs, and inform groundwater resource management decisions in the MDB.

Local-Scale Groundwater Sustainability Assessment Based on the Response to Groundwater Mining (MGSI): A Case Study of Da’an City, Jilin Province, China

Sustainable groundwater utilization is important for social and economic development. There is a need for groundwater sustainability assessment in small-scale areas lacking detailed mining data. Here, exploiting water level data series, we propose an indicator of groundwater sustainability based on the response to mining (MGSI) for better evaluation; it integrates groundwater data and spatio-temporal variability at a local scale. A decomposition coefficient was applied to decompose the pressure exerted by groundwater mining on the groundwater system for each monitoring well. It correlated with the groundwater response state. In Da’an City, Jilin Province, China, the appraised results revealed that the aquifer type exhibiting the greatest risk to groundwater sustainability changed from phreatic to confined during 2008–2017. The spatio-temporal distribution of different sustainability levels between and within the aquifers indicated that adjustment of the groundwater mining layout should be the focus of groundwater management in Da’an City. Additionally, the Mann–Kendall trend test and Sen’s slope trend analysis effectively explained the sustainable evolution of groundwater in Da’an City and confirmed the reliability of the MGSI method. The proposed method highlights the effects of groundwater mining on sustainability and helps us better understand the interaction between anthropogenic activities and groundwater resources.

Meteorological Variability and Groundwater Quality: Examples in Different Hydrogeological Settings

Rainfall and temperature variability causes changes in groundwater recharge that can also influence groundwater quality by different processes. The aim of this study is the analysis of the hydrogeochemical variations over time due to meteorological variability in two different study areas in Italy: an alluvial aquifer in the Piedmont Po plain and an alluvial-pyroclastic aquifer in the Campanian plain. The examined plains show groundwater with natural quality not satisfying the European drinking water standards, or anthropogenic contamination. The peculiar natural quality is due, in the Campanian plain, to the closeness of volcanic areas, and to the presence of reducing conditions. In Piedmont plain a test site is characterized by a point-source contamination by heavy metals, due to the presence of past industrial activities. In all the examined areas there is a diffuse nitrate contamination. The fluctuations of the ions As, F, Fe, Mn, Cr VI, NO3, and Cl were analyzed and compared, using statistical methods, with the variations over time in precipitation, temperature, and piezometric levels, sometimes significant. Results highlight the importance of the groundwater and meteorological monitoring and the key role of the recharge variation in the hydrogeochemical processes. The linking degree between rainfall/temperature variability and hydrogeochemistry is variable, in function of the typology of chemical species, their origin, and of the aquifer characteristics. The fluctuation of climate variables determines sudden changes in the geochemistry of shallow unconfined aquifers (e.g., in the Piedmont plain), while semiconfined or confined aquifers (e.g., in the Volturno-Regi Lagni plain) react with a greater delay to these variations. Moreover, natural quality is more affected by climatic variations than anthropogenic contamination, which is the result of multiple environmental and anthropic factors.