Acque Sotterranee - Italian Journal of Groundwater

Mapping saltwater intrusion via Electromagnetic Induction for planning a Managed Aquifer Recharge facility in Maltese island

Lorenzo De Carlo — 2024-03-28

In coastal areas, saltwater intrusion causes a depletion of the resource by reducing potable and irrigation freshwater supplies and causing severe deterioration of groundwater quality. This trend is observed in Pwales Valley, in the northern part of Malta, where the management of water resources plays a crucial role for the environmental sustainability of the area, given the importance of intensive agricultural activity along this valley. In order to tackle such a phenomenon, actions or adaptation measures against climate change are strongly required. For example, managed aquifer recharge (MAR) is an increasingly important water management strategy to maintain, enhance, and secure stressed groundwater systems and to protect and improve water quality. To accurately plan a MAR scheme, it is crucial to define a hydrogeological model of the studied area with the use of traditional hydrogeological measurements and innovative unconventional techniques. In recent years, electromagnetic induction measurements based on the induction of EM fields have been increasingly used for investigating saltwater intrusion dynamics due to their high sensitivity to salinity. In the study area of Pwales Valley, a managed aquifer recharge scheme is being planned, and, for this aim, a hydrogeological model has been developed through an electromagnetic induction survey. More than 20,000 apparent electrical conductivity (ECa) data points were collected to generate a quasi-3D high-resolution model of the electrical conductivity of the Pwales Valley. The results highlighted the spatial extension of the tongue-shape salt water intrusion from east to west along the valley, as well as some geological-hydrogeological peculiarities such as the thickness of the salt wedge and the irregular top surface of the bottom impermeable layer, otherwise undetectable with other direct techniques at the field scale resolution. The approach was confirmed to be a useful tool for effective hydrogeological characterization, essential for planning adaptation measures to a changing climate, such as the implementation of a managed aquifer recharge scheme.

Hydraulic characterization of Pwales aquifer in Malta Island preparatory for planning managed aquifer recharge (MAR) pilot plant

Maria Clementina Caputo — 2024-03-28

Whitin the aim to reduce the water demand by increasing water use efficiency and providing alternative water resources, and mainly to meet the demand of good quality irrigation water for agriculture, the Energy and Water Agency of Malta is planning to develop a Managed Aquifer Recharge pilot plant in Pwales Valley to improve the quantitative and qualitative status of the groundwater body. For this reason a detailed hydraulic characterization of the valley was carried out. Specifically, hydraulic properties of the rocks that constitute strata atop of the Pwales aquifer were determined by means of both laboratory measurements on samples and field test carried out in the studied area. The water retention and hydraulic conductivity functions, which relate the matric potential, ψ, and hydraulic conductivity, K, to the water content, θ, respectively, were measured using three experimental methods because each of them allows to obtain data points in a specific wet range. The water retention and hydraulic conductivity functions were measured on samples extracted from blocks of Upper Coralline Limestone formation, that hosts the aquifer, collected in three different quarries: Ghian Tuffieha, Mellieha and San Martin areas. The measured water retention and hydraulic conductivity data were fitted with LABROS SoilView Analysis software that allows to describe the functions and obtain the parameters which are crucial for modelling the water flow and transport processes in the critical zone. In addition, large ring infiltrometer test was carried out to determine the field saturated hydraulic conductivity, Kfs, and the average infiltration rate. Knowledge of the hydraulic characteristics of the Upper Coralline Limestone, completely missing in the scientific literature, allows developing a local groundwater-flow numerical model in order to better describe and understand how the water flows from the soil to the groundwater of the valley and visualize different environmental scenarios such as the potential effects of Managed Aquifer Recharge plant in the Pwales Coastal Groundwater Body.

Spatio-temporal variability of groundwater hydrochemical features in different hydrogeological settings in Piedmont and Campania regions (Italy), a comparative study

Daniele Cocca — 2024-03-28

The spatio-temporal evolution of groundwater chemistry has seen an increase in interest over the last decade at a global level. Identifying and discerning the sources of the natural and anthropogenic compounds and the actual hydrochemical processes, as well as their evolution, is essential to support a sustainable planning for managing and protecting groundwater resources at the present time and in the future. The main objective of this study is the comparison of two study areas in Italy (Piedmont and Campania Regions), different in their geographical and geological contexts and climate conditions, to highlight the similarities and differences in the hydrogeochemical behavior in space and time. Three main ions were considered (NO3 –, SO4 2–, Na+) and analyzed to identify the sources and hydrochemical processes responsible for their spatial distribution in the 2015-2020 period and evaluate the existence and the potential causes of trends in their concentration for the 2000-2020 period. Results highlight specific factors and processes distinguishing the spatial distribution and temporal variability of ion concentrations in Piedmont and Campania study areas. These processes are mainly related to the geological and geographical features of the study areas. In both areas, a significant influence of anthropogenic pressures emerges for both spatial and temporal evolutions, with remarkably increasing trends in NO3 – concentrations. In conclusion, some factors and processes emerge as site-specific, mainly related to the geological aspects and natural hydrochemical processes, whereas others are in common (i.e., anthropogenic impacts); thus, reinforcing the advantage of making comparative studies.

Arsenic in the groundwater aquifers of the Venetian Plain: geochemical modelling and occurrence of As-sulfides minerals, a review of data from the medio Brenta domain (Italy)

Fabio Tateo — 2024-02-29

The Venetian Plain is known for areas with high concentrations of arsenic (As) in groundwater (up to more than 400 μg/L; exceptionally 647μg/L, in selected areas). A study area was chosen, north of Padua, which exhibits typical residential, industrial, and agricultural characteristics similar to most Western countries and lacks hydrothermal, volcanic, or anthropogenic sources of arsenic. The pilot area was the focus of several studies which are reviewed in this note. The objectives of the studies were to verify the distribution of As concentrations in groundwater and sediments (mineralogical and geochemical analysis of groundwater sediments and of filtered and unfiltered groundwater) and to model the mobility of arsenic arising from water-rock interaction. The grain size of aquifer reservoirs includes gravel, sand, silt, and clay. The amount of organic matter in the aquifer sediments of the study area seems peculiar (higher) compared to other plains in the world; it influences the redox potential and the relative concentration of As in groundwater. Arsenic contamination in groundwater and redox conditions varied greatly in the area. Groundwater under oxidizing and highly reducing conditions had much lower arsenic concentrations compared to groundwater under intermediate reducing conditions. Arsenic minerals (such as realgar-pararealgar) occur in aquifer sediments and they were documented in the studied materials by different analytical techniques for the first time in the context of the Italian plains. Since these minerals are rare throughout the world in plain sediments not affected by volcanic or hydrothermal activity, their occurrence is a distinctive feature of the Venetian Plain aquifer. These arsenic minerals were found in peat sediments of the study area, consistent with geochemical modeling results, which require highly reducing conditions for their precipitation from groundwater. Modeling suggests that under oxidizing and up to slightly reducing conditions (from 200 mV to -50 mV), arsenic is adsorbed on solid phases, but a further decrease in redox potential leads arsenic desorption from solids and consequent groundwater contamination (from -50 mV to -250 mV). If the redox potential becomes even more negative (below -250 mV), geochemical conditions are favorable to the formation of arsenic sulfides. The precipitation of the realgar-pararealgar phases, predicted by the geochemical model, proceeds by extracting arsenic from the groundwater and quantitatively accounts for the lower arsenic concentration measured in the highly reducing groundwater of the study area.

Water quality aspects from Spanish sites to support managed aquifer recharge (MAR) guidelines not based on maximum allowable concentration standards

Enrique Fernandez-Escalante — 2024-03-28

Most countries that have technical guidelines or regulations for artificial recharge or managed aquifer recharge (MAR), that include water quality aspects are based on the establishment of standards or Maximum Allowable Concentrations (MACs) to regulate the quality of the water percolated or injected into an aquifer. The number of parameters in these guidelines vary considerably (from 6 in Spain to 156 in the USA) and often apply to all aquifers within administrative boundaries (e.g., national territory), regardless of the nature of the receiving medium, the depth of the water table, and other key factors. Eleven MAR systems in Spain have been studied (eight operational and three experimental, with limited number of data from three sites), characterising both, the recharge water quality and the water resulting from the interaction processes recharge water-soil-unsaturated zone-saturated zone of the aquifer. In all cases, an improved effect on groundwater quality is observed, even though some parameters in the recharge water don’t comply with the standards employed in some European countries, where this article focuses. The article suggests that regulating water quality for MAR through MACs at national level gives room for another alternative approach specific for each site. It might be recommendable to establish local standards at the regional or aquifer-wide level to better reflect the diversity of groundwater occurrence. As per the article, sectoral water authorities could receive more decision-making power on granting permits for MAR based on the quality of the hydrogeological and risk studies for each request. This would help reduce the application of the precautionary principle when in granting permission.

Mapping natural groundwater potential recharge zones using GIS-AHP in the Upper Cheliff alluvial aquifer, Algeria

Hanane Merouchi — 2024-03-28

Water scarcity is a big issue in arid and semi-arid regions. This challenge is particularly evident in the Upper Cheliff plain in Algeria, where the alluvial aquifer plays a vital role in drinking water supply and supporting irrigation. This aquifer faces high demand and quality issues. A study was conducted in this context, employing a cartographic approach to assess potential groundwater recharge from precipitation into the alluvial aquifer. The current study aimed at mapping zones with potential natural groundwater recharge zones by applying the Analytic Hierarchy Process (AHP) integrated within a Geographic Information System (GIS) environment, combining various factors that can influence recharge, such as rainfall, surface soil type, slope degree, land use and land cover, unsaturated zone, groundwater depth, and curve number. The map resulting from the analysis indicates that only 22% of the assessed area covers zones with very low and low potential recharge, 35% with moderate potential recharge zones, and 43% with high and very high potential recharge zones. This map reveals that the eastern region of the plain, from the cities of Djendel to Ain Soltane, is moderately to highly favorable for recharge. This is due to the natural recharge from rainfall and watercourse infiltration during dam release periods, excess irrigation water, and recharge from the Miocene sandstone aquifer in areas with direct aquifer contact. A validation process was performed using data from 66 wells distributed in this plain and it indicated that 48 wells exhibited good agreement with the resulting map, while 18 wells showed slight deviations. The results indicate an agreement of 72.72% between expected and exist number value of wells which confirming the good prediction of the AHP technique.

Hydrochemical and geoelectrical investigation to determine the origin and spatial distribution of the salinization of the unconfined Plio-Quaternary aquifer of Tabeditt, Southern Tunisia

Dalanda Ltifi — 2024-03-28

The expansion of irrigated agriculture and the overexploitation of groundwater in the Tabeditt region lead to a serious deterioration of the chemical quality of water. The compilation of hydrogeological and geophysical studies is essential in order to assess the quality of the Plio-Quaternary waters and to determine the origin of the salinization of these waters. In this study, hydrochemical analyses were carried out on groundwater samples in the Tabeditt region. Hydrochemical data have shown that the salinity in this area could exceed 6 g/L. The interpretation of major ion analyses demonstrates that mineralization is controlled by natural processes. The mineralization process consists of the dissolu-tion of evaporite minerals, namely gypsum, anhydrite, and halite. The geoelectrical study is carried out to obtain information about the distribution and quality of water in the Plio-Quaternary. Interpreta-tion of the resistivity models show the presence of two main zones: the first, near Tabeditt Wadi, is characterized by low values, indicating the influence of salt water in the groundwater and the second, located on the right bank of Wadi Jmal, is characterized by variable resistivity values, generally high, indicating the lateral changes in lithological facies, and the presence of fresh water. In such an arid region suffering from scarcity and degradation (or depletion) of water resources, it is important to implement a master plan that keeps under control the number of wells both known and unknown ones taping these aquifers.

Integration of geoelectrical, hydrochemical and geothermal data to identify the origin of thermal water in the foothills of the Tlemcen mountains, Northwestern Algeria

Somia Yousfi — 2024-03-28

In previous studies, the mean geothermal gradient of the Tlemcen region has been estimated as low (3.7°C/100m). The existing boreholes in the Remchi plain (North of the Tlemcen Mountains) reveal thermal waters (26-48°C) and a remarkable artesianism. To understand the hydrodynamics and origin of thermalism of this groundwater, we merged geophysical and physical-chemical data. Geophysical data allowed us to improve the resolution of the fault network, to estimate the thickness of various sandstone beds connected with the thermal reservoir and to delimit the productive aquifer. Chemical characteristics of waters have been used for a statistical analysis, which displayed two independent water clusters resulting from two hydrodynamic patterns throughout the aquifer. The hydrothermal analysis identifies the depth reached by water and the relationship between water circulation and the fault network. Comparison with previous studies allowed us to build a schematic geological model, which explains hydrodynamics, origin and role of this structure in the groundwater flow.

[ECHN-Italy: overview of activities from the last year and future challenges]

Alessia Di Giovanni — 2024-03-28

[Article in Italian]

ECHN-Italy: uno sguardo alle attività dell’anno passato e le sfide del futuro

[The activity plan for the realization of the Hydrogeological Map of Italy at 1:500,000 scale]

Rossella Maria Gafà — 2024-03-28

[Article in Italian]

Le attività avviate per la realizzazione di una Carta Idrogeologica d’Italia alla scala 1:500.000

[Groundwater and energy: shallow geothermal, i.e. heat-exchange, in urban areas]

Paolo Cerutti — 2024-03-28

[Article in Italian]

Acque sotterranee ed energia: geotermia superficiale, o geoscambio, in aree urbane

[What lies beneath? Brief history of exploration of volcanic lacustrine beds in the metropolitan area of Rome (central Italy)]

Alessio Argentieri — 2024-03-28

[Article in Italian]

Cosa c’è sotto? Breve storia dell’esplorazione dei fondali dei laghi vulcanici dell’area metropolitana di Roma Capitale (Italia centrale)

Flowpath 2023 Conference

Manuel Sapiano — 2024-03-28

The issue 175/1 of Acque Sotterranee – Italian Journal of Groundwater presents contributions from the Flowpath 2023 Conference which was held in Malta between the 14th and 16th of June. The scope of Flowpath focused on ensuring that hydrogeology can play an important role in supporting the development of groundwater management and protection policies; on strengthening the knowledge and research initiatives on emerging challenges to the groundwater environment and to highlight research initiatives undertaken in the Maltese islands, and improve technical cooperation between Maltese and Italian hydrogeologists. Flowpath brought together in Malta almost 200 hydrogeologists from Italy, Malta and six other countries who together contributed to 8 keynote speeches, 42 oral presentations and 45 posters. In fact this edition includes three papers from the Flowpath conference, two of which highlight joint work undertaken by researchers from Italy and Malta in the characterization of groundwater bodies.