Search

Groundwater is a primary water source which supplies more than 2 billion people. The increasing population and urbanization of rural areas stresses and depletes the groundwater systems, reducing the groundwater quality. Among the emerging contaminants, microplastics (MPs) are becoming an important issue due to their persistency in the environment. Seepage through the pores and fractures as well as the interaction with colloidal aggregates can partially affect the MPs dynamics in the subsoil, making the detection of the MPs in the groundwater systems challenging. Based on literature, a critical analysis of MPs in groundwater is presented from a hydrogeological point of view. In addition, a review of the MPs data potentially affecting the groundwater systems are included. MPs in groundwater may have several sources, including the atmosphere, the interaction with surface water bodies, urban infrastructures, or agricultural soils. The characterization of both the groundwater dynamics and the heterogeneity of MPs is suggested, proposing a new framework named “Hydrogeoplastic Model”. MPs detection methods aimed at characterizing the smaller fragments are necessary to clarify the fate of these contaminants in the aquifers. This review also aims to support future research on MP contamination in groundwater, pointing out the current knowledge and the future risks which could affect groundwater resources worldwide.

The definition of hydrogeological conceptual models sometimes suffers on uncertainties depending on the available dataset. The availability and the elaboration of long-term hydrogeological dataset allow ensuring a better definition of the aquifer dynamics and features. One of the main features, which can benefice on long-term datasets, is the recharge quantification. According to the literature, several methods exist to calculate the recharge and to get a deeper insight in recharge mode assessment. Most of them allow the quantification of infiltrating water by means of meteo-climatic data and land use information. In this research, a combined approach on hydrogeological time-series is proposed. The Cross-Correlation among the rainfall and the piezometric levels was applied to point out the response time of each aquifer layer. In addition, the Water Table Fluctuation method was used to indirectly quantify the recharge. The study area is the Roccamonfina Volcano caldera (Italy), where lateral inflows are absent, and the almost total natural groundwater discharge occurs in the Savone delle Ferriere stream. Here, a monitoring scheme of the major hydrogeological features was implemented. The local rainfall, the groundwater levels in 2 wells tapping the different aquifer layers, and the river stage of the Savone delle Ferriere stream were measured daily during the 2016-2017 period. The analyses defined different recharge modes for each aquifer layer. The aquifer recharge rates, calculated with different approaches, are comparable to each other and in line with the mean groundwater discharge through the Savone delle Ferriere streambed springs.

We present a new geometrical method capable of quantifying and illustrating the outcomes of a three-component mixing dynamics. In a three-component mixing scenario, classical algebraic equations and endmember mixing analysis (EMMA) can be used to quantify the contributions from each fraction. Three-component mixing of natural waters, either in an element–element plot or by using the EMMA mixing subspace is described by a triangular shaped distribution of sample points where each endmember is placed on an apex, while each side corresponds to the mixing function of the two endmembers placed at the apex, considering the third endmembers' contribution equal to zero. Along each side, the theoretical mixing fractions can be computed using mass balance equations. Samples with contributions from three endmembers will plot inside the triangle, while the homogeneous barycentric coordinate projections can be projected onto the three sides. The geochemistry observed in the mineralized Ferrarelle aquifer system (southern Italy) results from three-component mixing of groundwater, each with diagnostic geochemical compositions. The defined boundary conditions allow us to parameterize and validate the procedures for modelling mixing, including selection of suitable geochemical tracers.

A theoretical pattern for Fe and As co-precipitation was tested directly in a groundwater natural system. Several monitoring wells were sampled to identify the different endmembers that govern the hydrodynamics of the Ferrarelle Groundwater System in the Riardo Plain (Southern Italy). In agreement with recent investigations, we found a mix of a deep and a shallow component in different proportions, resulting in a specific chemical composition of groundwater in each well depending on the percentages of each component. The shallow component was characterized by EC ~ 430 µS/cm, Eh ~ 300 mV, Fe ~ 0.06 µmol/L and As ~ 0.01–0.12 µmol/L, while the deep component was characterized by EC ~ 3400 µS/cm, Eh ~ 170 mV, Fe ~ 140 µmol/L and As ~ 0.59 µmol/L. A general attenuation of As and Fe concentration that was not due to a simple dilution effect was observed in the mixing process. The oxidation of Fe(II) to Fe(III) produces solid precipitates which adsorb As from solution and then co-precipitate. The reactions pattern of Fe(II) oxidation and As adsorption gave a linear function between [As] and [Fe], where the angular coefficient depends on the [O2]/[H+] ratio. Chemical data obtained from our samples showed a very good agreement with this theoretical relationship. The investigated geochemical dynamics represented a natural process of attenuation of Fe and As, two undesirable elements that usually affect groundwater quality in volcanic aquifers in central-southern Italy, which are exploited to supply drinking water. Graphic abstract

The Riardo basin hosts groundwater exploited for the production of high quality, naturally sparkling, bottled water (e.g., Ferrarelle water), and circulating in a system constituted by highly fractured Mesozoic carbonates, overlain by more impervious volcanic rocks of the Roccamonfina complex. The two formations are locally in hydraulic connection and dislocated by deep-rooted faults. The study aimed at elucidating groundwater origin and circulation, using isotopic tracers (δ18O, δ2H, δ11B and 87Sr/86Sr) coupled to groundwater dating (Tritium, CFCs and SF6). Besides recharge by local precipitation over the Riardo hydrogeological basin, stable isotope ratios in water indicated an extra-basin recharge, likely from the elevated surrounding carbonate reliefs (e.g., Maggiore and Matese Mts.). The mineralization process, promoted by the deep CO2 flux, controls the B and Sr contents. However, their isotopic ratios did not allow discriminating between circulation in the volcanic and in the carbonate aquifers, as in the latter the isotopic composition differed from the original marine signature. Groundwater model ages ranged from ~ 30 years for the volcanic endmember to > 70 years for the deep, mineralized end-member, with longer circuits recharged at higher elevations. Overall, the results of this study were particularly relevant for mineral water exploitation. A recharge from outside the hydrogeological basin could be evidenced, especially for the more mineralized and valuable groundwater, and an active recent recharge was detected for the whole Riardo system. Both findings will contribute to the refinement of the hydrogeological model and water budget, and to a sustainable development of the resource.

Il famoso libro Groundwater (Freeze and Cherry 1979), un testo fondamentale per la formazione di qualsiasi idrogeologo, è ora disponibile anche in italiano, ed è scaricabile gratuitamente a questo indirizzo: http://hydrogeologistswithoutborders. org/wordpress/1979-italiano [...].

A local preliminary 2D model was built in the Riardo Plain in order to preliminary evaluate the regional hydrogeological conceptual model. The used finite element code was FeFlow 6.2 and calibration of data was performed via inverse modelling through FePEST (PEST code). A volcanic and a carbonate aquifer can be distinguished at regional scale. The multilayered volcanic aquifer presents a radial flow towards gaining streams and it is recharged by direct infiltration. Regional information about the carbonate aquifer are not available. The basement upraise and the fault systems allow the local mixing between the carbonate and volcanic aquifers. Recharge of the carbonate aquifer is likely to up-flow from the deep reservoir, but no direct information is available about rates and spatial distribution. Therefore, the aim of the 2D numerical model was to test the reliability of the hypothesis of possible bottom recharge through the carbonate basement, proposed in previous groundwater budget research. After a first steady state calibration of the model, transient calibration was performed to fit the groundwater levels of the carbonate and the volcanic aquifer monitored in 2003. The zenithal recharge was applied daily as calculated from the thermo pluviometric data elaborated by Thornthwaite’s method, and the vertical discretization of the aquifers was set according to the stratigraphic information. A constant bottom recharge was set as upflow through the carbonate basement. The calibration, performed over conductivity and specific storage, gave good results. The obtained budget parameters show the higher amount of the zenithal recharge (around 60%) over the carbonate recharge (around 40%), preliminary confirming the supposed recharge model.

Complex hydrogeological systems require detailed knowledge of aquifer dynamics to ensure appropriate and sustainable management of the groundwater resource. The Riardo Plain aquifer, southern Italy, is a strategic resource for conjunctive uses; nevertheless, the conceptual model still suffers some uncertainties due to the presence of a deep lateral inflow through the carbonate basement. Therefore, the realisation of a 3D numerical model at catchment scale needs preliminary tests to constrain the possible additional inflow rate, which is at the moment only estimated through the results of the groundwater budget calculation. A 2D section of the mixing area was modelled using FEFLOW in order to test the hypothesis of a combined recharge. Seven versions of the same model were calibrated over an increasing number of adjustable parameters according to their sensitivity. The most efficient model version was identified according to the calculated information criteria and the sum of squared-weighted residuals. In the second phase of the work, nine model scenarios characterised by different deep inflow rates were calibrated and validated according to the same procedure of the first model, in order to identify the range of possible acceptable solutions. The most likely deep inflow rate is 34 ± 4% of the total recharge, corresponding to an estimated deep inflow of 415 ± 50 L/s in the Riardo Plain aquifer through the carbonate basement. This methodological approach will be the basis of following numerical 3D numerical models of the Riardo Plain and can be a valuable tool in conceptualising similar mineral water areas.

This paper supports the ‘Hydrogeological map of the Sabatini Volcanic District’. The map provides an overview of the hydrogeological setting of the Sabatini Volcanic District, using experimental water level data integrated with former volcanological and hydrogeological studies. The 1:50,000 scale map was produced in order to provide support to local authorities and professionals working on groundwater management. Fifteen hydrogeological complexes were defined based on volcanological properties and hydrogeological conditions.

The dynamics of natural contamination by Al and Fe colloids in volcanic aquifers of central-southern Italy were investigated. Localized perched aquifers, and their relative discharges, are strongly affected by the presence of massive suspended solids, which confer a white-lacteous coloration to the water. This phenomenon occasionally caused the interruption of water distribution due to the exceeding of Al and Fe concentrations in aquifers exploited for human supply. The cause was ascribed to water seepage from perched aquifers. Water discharges affected by such contamination was investigated for the Rocca Ripesena area (north-eastern sector of Vulsini Volcanic District) and for the Rianale Stream Valley (Roccamonfina Volcanic Complex). Hydrogeological survey of both areas confirmed the presence of perched aquifers not previously considered due to their low productivity. Pluviometric data and chemical parameters were periodically monitored. Water mineralization decreased with increasing rainfall, conversely Al and Fe concentrations increased. Statistical analysis confirmed the dependence of all the chemical variables on rock leaching, with the sole exception of Al and Fe which were imputed to colloids mobilization from local, strongly pedogenized pyroclastic material. The similarities in hydrogeological settings and mobilization dynamics in both areas suggest that the Al and Fe colloidal contamination should be more abundant than currently known in quaternary volcanic areas.