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The combination of several factors related both to human pressure as well as natural issues could lead to a marked alteration of the groundwater budget terms and a decrease in groundwater availability. The basal aquifer of the Sibillini Mts. is a strategic resource of drinking water in the central sector of Apennine (Italy). The seismic sequence that occurred in this area in 2016 induced transient and sustained modifications in the aquifer settings. Springs located on the western side of the Sibillini Mts. were characterized by an increased discharge, while in contrast, the eastern springs suffered an intense drop in their groundwater discharge. In 2017, a drought period started immediately after the exhaustion of the seismic sequence effect. The comparison between the recharge and discharge of the major springs in the 2000–2020 period allowed the definition of the different responses of the aquifer to the co-occurrence of earthquakes and climatic events. The hydrodynamic alteration triggered by the earthquake induced a huge depletion of the groundwater stored in the eastern sector of the basal aquifer (at least 50 × 106 m3). The scarce recharge occurring in the following drought period (more than 30% of the average annual value) was not enough to restore the groundwater resources, causing a serious drinking water supply crisis in the main tapped springs in the eastern sector of the aquifer.

In the Dolomites mountain range, the most productive aquifers are found in porous valley-fill deposits, such as alluvial, glacial and other heterogeneous types of clastic sediments. These deposits store significant amounts of groundwater resources and are laterally bordered by steep carbonate reliefs, which in turn constitute fractured high-yielding aquifers. The talus cones and slopes at the base of the rock cliffs play the role of hydraulic connection between the fractured aquifers and the porous aquifers at the valley floor. This situation is very well represented in the San Lucano glacial valley system in the Dolomite Mountains (Italy), where average groundwater resources were estimated at approximately 2 m3/s. The hydrogeological data collected in this study allowed to identify the interaction between stream discharge and the saturated zone of the aquifers and to define apreliminary model of recharge and storage of the valley-fill aquifer.

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.

One of the major challenges for the sustainable development of the federal capital territory of Abuja (Nigeria) is related to the access to safe fresh water resources. This area lies within the drought prone parts of the Sahel region. As in many regions of the world there has been growing competing demands for fresh water as a result of population growth and groundwater quality degradation. In this context, the paucity of data and in depth knowledge of aquifer features and groundwater flow makes groundwater management even more complex, with a severe impact on access to safe water resources for the local populations. To address this challenge, the purpose of the presented research is to generate information on aquifer settings and its vulnerability and on the qualitative and quantitative assessment of the available groundwater resources. Remote sensing and GIS were applied to improve the available information on groundwater resources of Abuja. Fundamental information such as recharge rate, availability and vulnerability of groundwater to pollution was determined. Aquifer vulnerability zones were delineated using the DRASTIC model by integrating layers of depth to groundwater, aquifer recharge, aquifer media, soil type, topography, impact of vadose zone and hydraulic conductivity. The study area covers about 8000km². The elevation ranges from 62 to 843m a.s.l. with the highest elevations at the North Eastern parts and the lowest elevations at the South Western parts of the study area. There are three soil types in the area, the silty clay, silt loam and clay with clay being the predominant soil type. The five major rock types in the area include migmatite gneiss, schist and metasediment, sandstone and river alluvium, granite and quartzite. The aquifer type is phreatic and the depth to groundwater ranges from 2.8 to 21.9 m. The high recharge areas occurred mostly in highly fractured areas covered with metasedimentary rocks, migmatite gneiss and sandstones. The groundwater vulnerability zones in the study area were grouped into four classes: High, moderate, low and very low. The highly vulnerable zones are the North Eastern parts of the study area covering most parts of Bwari and parts of the municipal council areas and also the Southern parts of the study area covering parts of Kuje and Abaji. They constitute the highly fractured areas covered with silt loam soil type. The very low vulnerable zones are the North Western and Central parts covering mostly Gwgwalada and Kwali areas. This study demonstrates that GIS and remote sensing techniques are efficient and cost effective tool for delineation of groundwater vulnerability zones. The information obtained will be used as a basis for a geochemical characterization of groundwater quality in the region with the overall goal of supporting new groundwater management plans in the region.

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.

Fin dalla sua costituzione, il gruppo ECHN-Italy mira ad incoraggiare il coinvolgimento nell’Associazione IAH dei giovani idrogeologi italiani, promuovendo il dibattito e la condivisione di conoscenze ed esperienze sulle principali problematiche idrogeologiche del nostro Paese e facilitando l’interazione con i membri del Comitato IAH-Italy [...].

The aim of the present map is to illustrate a detailed pre-earthquake hydrogeological conceptual model of the Sibillini Mts. This area was struck by a prolonged seismic sequence of up to Mw 6.5 in 2016. Geological, tectonic, and hydrogeological data were collected from the literature before 2016, subsequently standardized and re-interpretated with the aim of presenting a hydrogeological map (1:50,000 scale) of the Sibillini Mts. carbonate system (Central Italy). The map is supported by 11 hydrogeological both cross and longitudinal sections, which show the underground spatial relationship between aquifers, aquicludes, and tectonic elements. This Map provides a model of comparison for the new hydrogeological conditions emerging from the post-seismic research.

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 sustained increase in spring discharges was monitored after the 2016 Central Italy seismic sequence in the fractured carbonate aquifer of Valnerina–Sibillini Mts. The groundwater surplus recorded between August 2016 and November 2017 was determined to be between 400 and 500 × 106 m3. In fractured aquifers, the post-seismic rise in spring discharges is generally attributed to an increase in bulk permeability caused by the fracture cleaning effect, which is induced by pore pressure propagation. In the studied aquifers, the large amount of additional discharge cannot only be attributed to the enhanced permeability, which was evaluated to be less than 20% after each main seismic event. A detailed analysis of the spring discharge hydrographs and of the water level at five gauging stations was carried out to determine the possible causes of this sudden increase in groundwater outflow. Taking into account the geological and structural framework, a conceptual model of a basin-in-series has been adopted to describe the complex hydrogeological setting, where the thrusts and extensional faults have clearly influenced the groundwater flow directions before and after the seismic sequence. The prevalent portion of the total post-seismic discharge surplus not explained by the increase in permeability has been attributed to changes in the hydraulic gradient that caused seismogenic fault rupture and the disruption in the upgradient sector of the aquifer. The additional flow calculated through the breach of the pre-existing hydrostructural barrier corresponds to approximately 470 × 106 m3. This value is consistent with the total discharge increase measured in the whole study area, validating the proposed conceptual model. Consequently, a shift in the piezometric divide of the hydrogeological system has been induced, causing a potentially permanent change that lowers the discharge amount of the eastern springs.

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.

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The urban development plan of left bank of the Tiber river Delta preserved a 9 km2 stretch of dune belt with a monumental coastal pine forest (Castelfusano forest), which is nowadays portion of a natural reserve managed by Municipality of Rome. The forest was largely destroyed by a first huge fire in July 2000 and by another one in July 2017. A reforestation project involved the installation of a monitoring network composed by 21 piezometers to check the groundwater depth and its degree of salinization after the 2000 fire. By examining series of water head measurements and chemical -physical parameters carried out from 2002 up today, the current research aims to analyse the effects of 2000 and 2017 fires on the recharge process. The first result consists in the definition of the hydrogeological conceptual models of the dune aquifer: a shallow fresh aquifer overlapping two deeper confined salinized aquifers. The comparison between the amount of the yearly recharge, evaluated in different periods, showed a significant recharge rate decrease (about 36%) to be attributed likely at the 2000 fire effect. The research is still ongoing in order to verify and detail the changes of the recharge processes induced by the 2000 and 2017 fires.

Groundwater management authorities usually use groundwater budget calculations to evaluate the sustainability of withdrawals for different purposes. The groundwater budget calculation does not always provide reliable information, and it must often be supported by further aquifer monitoring in the case of hydraulic connections between neighboring aquifers. The Riardo Plain aquifer is a strategic drinking resource for more than 100,000 people, water storage for 60 km2 of irrigated land, and the source of a mineral water bottling plant. Over a long period, the comparison between the direct recharge and the estimated natural outflow and withdrawals highlights a severe water deficit of approximately 40% of the total groundwater outflow. A groundwater budget deficit should be a clue to the aquifer depletion, but the results of long-term water level monitoring allowed the observation of the good condition of this aquifer. In fact, in the Riardo Plain, the calculated deficit is not comparable to the aquifer monitoring data acquired in the same period (1992–2014). The small oscillations of the groundwater level and the almost stable streambed spring discharge allows the presumption of an additional aquifer recharge source. The confined carbonate aquifer locally mixes with the above volcanic aquifer, providing an externally stable recharge that reduces the effects of the local rainfall variability. The combined approach of the groundwater budget results and long-term aquifer monitoring (spring discharge and/or hydraulic head oscillation) provides information about significant external groundwater exchanges, even if unidentified by field measurements, and supports the stakeholders in groundwater resource management.

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 exploitation of groundwater resources must always keep in account the geology and hydrogeological settings of the catchment basin for the sustainability of withdrawals, in order not to overexploit the aquifer. Especially, in the case of mineral water extraction, even more attention should be paid to understand what are the water-rock-gases interaction mechanisms, which allow obtaining a specific water chemistry. The case of Ferrarelle mineral water (western sector of Riardo Plain, Caserta) is particularly complex. Through the acquisition of a great amount of former geological and hydrogeological data and by new hydrogeological surveys, it has been possible to distinguish the aquifer levels, distinguishing four circulations over the Roccamonfina Volcano and in the Riardo Plain. The presence of volcanic and volcaniclastic deposits deriving from the Roccamonfina Volcano which cover a highlytectonized carbonate bedrock, allows the formation of two aquifers in hydraulic continuity. This mixing between the two aquifers allows, with the ascent of deep CO2 through faults in the carbonate bedrock, the formation of the typical chemical composition of the mineral water Ferrarelle. In the eastern sector of the plain, it is possible to distinguish the volcanic aquifer from the carbonate one, probably due to the presence of low permeability deposits.

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.

The volcanic system of Ischia is characterized by an intense hydrothermal activity, documented since the early 16th century by the study of Iasolino (1588), which represents the first systematic analysis of the thermal springs of the island for therapeutic purposes. Later studies partially contributed to the enhancement of knowledge on the volcanic, hydrogeological and hydrothermal features of the island, highlighting the strong interaction between hydrothermal flowpaths and volcano- tectonic processes. The reconstruction of the interplay between hydrothermal and magmatic system becomes, therefore, a fundamental element for territorial planning, not only in terms of management of the huge water and geothermal resource, but also in a perspective of prevention and mitigation of volcanic risk. Thermal springs, fumaroles and mud deposits give beginning clues about deep hydrothermal conditions. Till now at Ischia, the local geochemical characterization of fluids and groundwater has been used for the definition of the origin and structure of the hydrothermal system as a whole, as the hydrogeological information is incomplete. However, volcanic hydrothermal systems, such as that characterizes the island of Ischia, are particularly difficult to analyze and outline, as the groundwater resources are the result of a complex and dynamic mixing among meteoric water, sea water and deep fluids. In such cases, the need for an interdisciplinary approach is evident, involving knowledge and research methods ranging from geology to volcanology, geophysics, geochemistry and hydrogeology. With particular reference to the functional and structural representation of the geothermal system of the Ischia island and the resulting correlations with the volcano-tectonic processes, the examination of previous information highlights the need to update and improve the knowledge on groundwater hydrodynamics and mineralization processes. Therefore, the present study aims at a strongly interdisciplinary action that, starting from the design and implementation of a database on the existing geological/volcanological and hydrogeological information, will contribute to highlight the critical issues, define an operating scheme of the hydro-geo-thermal system of the island of Ischia, and upgrade its hydrogeological, geochemical and volcanic monitoring system. The preliminary results improved the definition of the hydrogeological complexes and advanced knowledge of the groundwater flow conditions.