Hydrogeochemical Characterization of Groundwater from Fissured Aquifers in the Angovia Mine Operating Permit Area (Central-West Côte d’Ivoire)

The main objective of this study is to determine the hydrogeochemical specificities of the groundwater of the Angovia mine operating permit, located in the Yaouré mountains in the center-west of Côte d’Ivoire. To do so, descriptive and multivariate statistical analysis methods with the SOM (Self Organizing Maps) algorithm were applied to the physicochemical parameters of 17 boreholes using the calcite (ISC) and dolomite (ISD) saturation indices. The results obtained have shown that the groundwater in the Angovia mine operating permit area has an average temperature of 27.52°C (long rainy season) and 27.87&degC (long dry season) and has an average pH of 7.09 ± 0.35 during the main rainy season and 7.32 ± 0.35 during the main dry season. They are mineralized with an average electrical conductivity of 505.98 ± 302.85 μS/cm during the long rainy season and with 450.33 ± 233.74 μS/cm as average during the long dry season. The main phenomena at the origin of groundwater mineralization are water residence time, oxidation-reduction and surface inflow. The study of the relative age of the water shows that the groundwater in the Angovia mine operating permit area is mainly undersaturated with respect to calcite and dolomite. They are therefore very old in the aquifer with a slow circulation speed during the long rainy season and the long dry season.

Water-induced physicochemical and pore changes in limestone for surrounding rock across pressure aquifers

Osmotic water alters the physicochemical properties and internal structures of limestone.This issue is particularly critical in tunnel construction across mountainous regions with aquifers,where pressurized groundwater can destabilize the limestone-based surrounding rock.Thus,systematic research into the physicochemical properties and pore structure changes in the limestone under pressurized water is essential.Additionally,it is essential to develop an interpretable mathematical model to accurately depict how pressurized osmotic water weakens limestone.In this research,a specialized device was designed to simulate the process of osmotic laminar flow within limestone.Then,four main tests were conducted:mass loss,acoustic emission(AE),mercury intrusion porosimetry(MIP),and fluorescence analysis.Experimental results gained from tests led to the development of a“Particle-pore throat-water film”model.Proposed model explains water-induced physicochemical and pore changes in limestone under osmotic pressure and reveals evolutionary mechanisms as pressure increases.Based on experimental results and model,we found that osmotic pressure not only alters limestone composition but also affects pore throats larger than 0.1μm.Furthermore,osmotic pressure expands pore throats,enhancing pore structure uniformity,interconnectivity,and permeability.These effects are observed at a threshold of 7.5 MPa,where cohesive forces within the mineral lattice are surpassed,leading to the breakdown of erosion-resistant layer and a significant increase in hydrochemical erosion.

Key aspects of underground hydrogen storage in depleted hydrocarbon reservoirs and saline aquifers:A review and understanding

Underground hydrogen storage is critical for renewable energy integration and sustainability.Saline aquifers and depleted oil and gas reservoirs represent viable large-scale hydrogen storage solutions due to their capacity and availability.This paper provides a comparative analysis of the current status of hydrogen storage in various environments.Additionally,it assesses the geological compatibility,capacity,and security of these storage environments with minimal leakage and degradation.An in-depth analysis was also conducted on the economic and environmental issues that impact the hydrogen storage.In addition,the capacity of these structures was also clarified,and it is similar to storing carbon dioxide,except for the cushion gas that is injected with hydrogen to provide pressure when withdrawing from the store to increase demand.This research also discusses the pros and cons of hydrogen storage in saline aquifers and depleted oil and gas reservoirs.Advantages include numerous storage sites,compatibility with existing infrastructure,and the possibility to repurpose declining oil and gas assets.Specifically,it was identified that depleted gas reservoirs are better for hydrogen gas storage than depleted oil reservoirs because hydrogen gas may interact with the oil.The saline aquifers rank third because of uncertainty,limited capacity,construction and injection costs.The properties that affect the hydrogen injection process were also discussed in terms of solid,fluid,and solid-fluid properties.In all structures,successful implementation requires characterizing sites,monitoring and managing risks,and designing efficient storage methods.The findings expand hydrogen storage technology and enable a renewable energy-based energy system.

Harnessing machine learning tools for water quality assessment in the Kebili shallow aquifers,Southwestern Tunisia

An integrated method that implements multivariate statistical analysis and ML methods to evaluate groundwater quality of the shallow aquifers of the Djerid and Kebili district,Southern Tunisia,was adopted.An evaluation of their suitability for irrigation and/or drinking purposes is necessary.A comprehensive hydrochemical assessment of 52 samples with entropy weighted water quality index(EWQI)was also proposed.Eleven water parameters were calculated to ascertain the potential use of those resources in irrigation and drinking.Multivariate analysis showed two main components with Dim1(variance=62.3%)and Dim.2(variance=22%),due to the bicarbonate,dissolution,and evaporation and the intrusion of drainage water.The evaluation of water quality has been carried out using EWQI model.The calculated EWQI for the Djerid and Kebili waters(i.e.,52 samples)varied between 7.5 and 152.62,indicating a range of 145.12.A mean of 79.12 was lower than the median(88.47).From the calculation of EWQI,only 14 samples are not suitable for irrigation because of their poor to extremely poor quality(26.92%).The bivariate plot showed high correlation for EWQI~TH(r=0.93),EWQI~SAR(r=0.87),indicating that water quality depended on those parameters.Diff erent ML algorithms were successfully applied for the water quality classifi cation.Our results indicated high prediction accuracy(SVM>LDA>ANN>kNN)and perfect classifi cation for kNN,LDA and Naive Bayes.For the purposes of developing the prediction models,the dataset was divided into two groups:training(80%)and testing(20%).To evaluate the models’performance,RMSE,MSE,MAE and R^(2) metrics were used.kNN(R^(2)=0.9359,MAE=6.49,MSE=79.00)and LDA(accuracy=97.56%;kappa=96.21%)achieved high accuracy.Moreover,linear regression indicated high correlation for both training(R^(2)=0.9727)and testing data(0.9890).This well confi rmed the validity of LDA algorithm in predicting water quality.Cross validation showed a high accuracy(92.31%),high sensitivity(89.47%)and high specifi city(95%).These fi ndings are fundamentally important for an integrated water resource management in a larger context of sustainable development of the Kebili district.

Modeling of Total Dissolved Solids (TDS) and Sodium Absorption Ratio (SAR) in the Edwards-Trinity Plateau and Ogallala Aquifers in the Midland-Odessa Region Using Random Forest Regression and eXtreme Gradient Boosting

Efficient water quality monitoring and ensuring the safety of drinking water by government agencies in areas where the resource is constantly depleted due to anthropogenic or natural factors cannot be overemphasized. The above statement holds for West Texas, Midland, and Odessa Precisely. Two machine learning regression algorithms (Random Forest and XGBoost) were employed to develop models for the prediction of total dissolved solids (TDS) and sodium absorption ratio (SAR) for efficient water quality monitoring of two vital aquifers: Edward-Trinity (plateau), and Ogallala aquifers. These two aquifers have contributed immensely to providing water for different uses ranging from domestic, agricultural, industrial, etc. The data was obtained from the Texas Water Development Board (TWDB). The XGBoost and Random Forest models used in this study gave an accurate prediction of observed data (TDS and SAR) for both the Edward-Trinity (plateau) and Ogallala aquifers with the R2 values consistently greater than 0.83. The Random Forest model gave a better prediction of TDS and SAR concentration with an average R, MAE, RMSE and MSE of 0.977, 0.015, 0.029 and 0.00, respectively. For the XGBoost, an average R, MAE, RMSE, and MSE of 0.953, 0.016, 0.037 and 0.00, respectively, were achieved. The overall performance of the models produced was impressive. From this study, we can clearly understand that Random Forest and XGBoost are appropriate for water quality prediction and monitoring in an area of high hydrocarbon activities like Midland and Odessa and West Texas at large.

The Damaging Effects of Abstracting the Deep Aquifers’Groundwater in Jordan-Quality Constraints

The deep aquifers in Jordan contain non-renewable and fossil groundwater and their extraction is quasi a mining process, which ends in the depletion of these resources. Although aquifers in the majority of groundwater basins in Jordan are vertically and horizontally interconnected stratification in different water quality horizons with generally increasing water salinity with the depth is observed. Many officials and planners advocate the extraction of deep salty and brackish water to be desalinated and used in household, industrial, and agricultural uses. In this article, the quality of the groundwater in the different deep aquifers and areas in Jordan is discussed. The results of this study show that the consequences of the deep groundwater exploitation are not restricted to depletion of the deep aquifers but also that the overlying fresh groundwater will, due to vertical and horizontal interconnectedness of the different aquifers, percolate down to replace the extracted deep groundwater. This will cause the down-percolating fresh groundwater to become salinized in the deep saline aquifers, which means that extracting the deep brackish and saline groundwater is not only an emptying process of the deep groundwater but also it is an emptying process of the fresh groundwater overlying them. The results allow to conclude that any extraction of the deep groundwater in areas lying to the north of Ras en Naqab Escarpment will have damaging impacts on the fresh groundwater in the overlying fresh groundwater aquifers. This article strongly advises not to extract the deep brackish and saline groundwater, but to conserve that groundwater as a base supporting the overlying fresh groundwater resources, and that will help in protecting the thermal mineralized water springs used in spas originating from these deep aquifers. The increasing water needs of the country can be covered by the desalination of seawater at Aqaba, which is the only viable option for Jordan at present and in the coming decades.

Potential evaluation of saline aquifers for the geological storage of carbon dioxide: A case study of saline aquifers in the Qian-5 member in northeastern Ordos Basin

The well-developed coal electricity generation and coal chemical industries have led to huge carbon dioxide(CO_(2))emissions in the northeastern Ordos Basin.The geological storage of CO_(2) in saline aquifers is an effective backup way to achieve carbon neutrality.In this case,the potential of saline aquifers for CO_(2) storage serves as a critical basis for subsequent geological storage project.This study calculated the technical control capacities of CO_(2) of the saline aquifers in the fifth member of the Shiqianfeng Formation(the Qian-5 member)based on the statistical analysis of the logging and the drilling and core data from more than 200 wells in the northeastern Ordos Basin,as well as the sedimentary facies,formation lithology,and saline aquifer development patterns of the Qian-5 member.The results show that(1)the reservoirs of saline aquifers in the Qian-5 member,which comprise distributary channel sand bodies of deltaic plains,feature low porosities and permeabilities;(2)The study area hosts three NNE-directed saline aquifer zones,where saline aquifers generally have a single-layer thickness of 3‒8 m and a cumulative thickness of 8‒24 m;(3)The saline aquifers of the Qian-5 member have a total technical control capacity of CO_(2) of 119.25×10^(6) t.With the largest scale and the highest technical control capacity(accounting for 61%of the total technical control capacity),the Jinjie-Yulin saline aquifer zone is an important prospect area for the geological storage of CO_(2) in the saline aquifers of the Qian-5 member in the study area.

Dealing with the Spatial Synthetic Heterogeneity of Aquifers in the North China Plain:A Case Study of Luancheng County in Hebei Province

The complexity of alluvial-pluvial fan depositional systems makes the detailed characterization of their heterogeneity difficult, yet such a detailed characterization is commonly needed for construction of reliable groundwater models. Traditional models mainly focus on using a single aquifer property to qualitatively or semi-quantitatively characterize the heterogeneity of aquifer, so that they are unable to quantitatively reflect the synthetic heterogeneity of all aquifer properties. In this paper, we propose the heterogeneity synthetic index （HSI） for quantitative characterization of synthetic heterogeneity of an aquifer. The proposed calculation process involves four steps： （1） estimation of the hydraulic conductivity of a sediment sample using the cloud-Markov model, （2） establishment of the sedimentary microfacies distribution model through the Markov chain, （3） characterization of the distribution model of hydrogeological parameters using the improved sequential simulation method according to the ＂facies-controlled modeling＂ technique, and （4） application of the entropy weight method to calculate the weight coefficient of the above aquifer properties. The HSI of an aquifer is calculated by superposition of these models according to the corresponding weight coefficient. This approach was applied to the Luancheng aquifer deposit in the southeast Hutuo River alluvial-pluvial fan in the North China Plain （NCP）. The results have demonstrated that aquifer 3 which was formed in the middle Pleistocene has the strongest heterogeneity, with an HSI of 0.25-0.75. Aquifer 4 formed in the early Pleistocene shows an intermediate heterogeneity, with the HSI ranging 0.35-0.75. The weakest heterogeneity was found in aquifers 1 and 2 formed in the Holocene and late Pleistocene, with HSI values of 0.40-0.75 and 0.40- 0.80, respectively. The heterogeneity of all the four aquifers is relatively strong in the radial direction of the Huai River alluvial-pluvial fan due to the abrupt change of microfacies. In contrast, in the radial direction of the Hutuo River alluvial-pluvial fan, the microfacies change mildly, and the continuity of hydrogeological parameters is better, which has resulted in weaker heterogeneity of the four aquifers in this direction. Findings suggest that the sedimentary environment has significant effects on the aquifer heterogeneity. Considering that there are many aquifer properties, HSI can quantitatively characterize the synthetic heterogeneity of the aquifer and describe the influence of each aquifer property on the synthetic heterogeneity of the aquifer according to its weight coefficient. Thus the HSI approach can be successfully used to deal with the spatial heterogeneity of aquifer and provide a foundation for studies on contaminant transport.

Characteristics of CO_2 sequestration in saline aquifers

Storage of CO2 in saline aquifers is a viable option for reducing the amount of CO2 released to the atmosphere. This paper provides an overall review of CO2 sequestration in saline aquifers. First, the principles of CO2 sequestration are presented, including CO2 phase behavior, CO2-water-rock interaction, and CO2 trapping mechanisms. Then storage capacity and CO2 injectivity are discussed as the main determinants of the storage potential of saline aquifers. Next, a site section process is addressed considering basin characteristics, reservoir characteristics, and economic and social concerns. Three main procedures are then presented to investigate the suitability of a site for CO2 sequestration, including site screening, detailed site characterization, and pilot field-scale test. The methods for these procedures are also presented, such as traditional site characterization methods, laboratory experiments, and numerical simulation. Finally, some operational aspects of sequestration are discussed, including well type, injection rate, CO2 purity, and injection strategy.

A geologically-based approach to map arsenic risk in crystalline aquifers:Analysis of the Tampere region, Finland

The study illustrates the critical role of accurate geological structural mapping to delineate crystalline aquifer zones more prone to high health risk due to elevated dissolved As in drinking wells.The analysis revisits the results from more than 1200 groundwater samples collected over ten years from domestic wells across the Tampere region (Finland).It is demonstrated that the highest dissolved As concentrations in the region (up to 2230 mg/L) are exclusively found near major faults and deformation zones (FDZs) detected via geophysical and geological surveys,and that a clear correlation exists between dissolved concentrations and the distance from the FDZs (r).Almost all values exceeding the drinking water limit (10 mg/L) occur at r < 8 km,while concentrations above 100 mg/L occur at r < 4 km.Solidphase As concentrations in bedrock show less dependency on FDZ than aqueous concentrations.This behavior is explained considering different mechanisms,which include enhanced sulfide oxidation and fracture connectivity,promoting preferential transport of dissolved As to FDZs and mixing of waters from different redox zones,mobilizing preferentially As(III) or As(V).Fe hydro-oxides may also precipitate/ dissolve preferentially because of FDZs,while residence time may influence the contact time between water and As-bearing minerals.It is concluded that the accurate mapping of FDZs,and in general of structural geology,provides an important preliminary information to identify where localized,sitespecific characterization of hydrogeology and geochemistry is more urgent to reduce As-related health risk from groundwater intake.

Optimal Groundwater Development in Coastal Aquifers Near Beihai, China

Groundwater resources occur in a multi aquifer system in the alluvial coastal plain near Beihai, China. The aquifers receive recharge from precipitation, canal and reservoir infiltration, and discharge through subterranean drainage into the sea and through artificial pumping. A quasi three dimensional finite element model has been used to simulate the spatial and temporal distribution of groundwater levels in the aquifers. Various input parameters were considered in the simulation model. A linear optimization model has been developed for groundwater development within the coastal aquifers. The objective function of the model is to maximize the total groundwater pumpage from the confined aquifer. The control of sea water intrusion is examined by the restriction of the water levels at points along the coast and of the pumping rates in coastal management cells. The response matrix used in the optimization model was generated from the simulation model by forecasting drawdown produced by pumping at a unit impulse discharge. Groundwater development can be primarily optimized by the alteration of the pumping rates of the existing wells.

Hydrogeochemical and multi-tracer investigations of arsenic-affected aquifers in semi-arid West Africa

The semi-arid Sahel regions ofWest Africa rely heavily on groundwater from shallow to moderately deep (<100 m b.g.l.) crystalline bedrock aquifers for drinking water production.Groundwater quality may be affected by high geogenic arsenic (As) concentrations (>10 μg/L) stemming from the oxidation of sulphide minerals (pyrite,arsenopyrite) in mineralised zones.These aquifers are still little investigated,especially concerning groundwater residence times and the influence of the annual monsoon season on groundwater chemistry.To gain insights on the temporal aspects of As contamination,we have used isotope tracers (noble gases,3H,stable water isotopes (2H,18O)) and performed hydrochemical analyses on groundwater abstracted from tube wells and dug wells in a small study area in southwestern Burkina Faso.Results revealed a great variability in groundwater properties (e.g.redox conditions,As concentrations,water level,residence time) over spatial scales of only a few hundred metres,characteristic of the highly heterogeneous fractured underground.Elevated As levels are found in oxic groundwater of circum-neutral pH and show little relation with any of the measured parameters.Arsenic concentrations are relatively stable over the course of the year,with little effect seen by the monsoon.Groundwater residence time does not seem to have an influence on As concentrations,as elevated As can be found both in groundwater with short (<50 a) and long (>10^3 a) residence times as indicated by 3He/4He ratios spanning three orders of magnitude.These results support the hypothesis that the proximity to mineralised zones is the most crucial factor controlling As concentrations in the observed redox/pH conditions.The existence of very old water portions with residence times >10^3 years already at depths of <50 m b.g.l.is a new finding for the shallow fractured bedrock aquifers of Burkina Faso,suggesting that overexploitation of these relatively low-yielding aquifers may be an issue in the future.

Sensitivity analysis of CO_2 sequestration in saline aquifers

Carbon capture and storage （CCS） technology has been considered as an important method for reducing greenhouse gas emissions and for mitigating global climate change. Three primary options are being considered for large-scale storage of CO2 in subsurface formations： oil and gas reservoirs, deep saline aquifers, and coal beds. There are very many large saline aquifers around the world, which could make a big contribution to mitigating global warming. However, we have much less understanding of saline aquifers than oil and gas reservoirs. Several mechanisms are involved in the storage of CO2 in deep saline aquifers, but the ultimate goal of injection of CO2 into the aquifers containing salt water is to dissolve the CO2 in the water. So it is important to study the solubility trapping and sensitivity factors of CO2 in saline aquifers. This paper presents results of modeling CO2 storage in a saline aquifer using the commercial reservoir simulator ECLIPSE. The objective of this study was to better understand the CO2/brine phase behavior （PVT properties） and quantitatively estimate the most important CO2 storage mechanism in brine-solubility trapping. This would provide a tool by performing theoretical and numerical studies that help to understand the feasibility of CO2 geological storage. A 3-dimensional, 2-phase （water/gas） conceptional reservoir model used finite, homogenous and isothermal formations into which CO2 is injected at a constant rate. The effects of main parameters were studied, including the vertical to horizontal permeability ratio kv/kh, salinity, and residual phase saturations. The results show that the vertical to horizontal permeability ratio has a significant effect on CO2 storage. Moreover, more CO2 dissolves in the brine at lower kv/kh values.

Identification of Contaminant Source Characteristics and Monitoring Network Design in Groundwater Aquifers: An Overview

The groundwater system is often polluted by different sources of contamination where the sources are difficult to detect. The presence of contamination in groundwater poses significant challenges to its delineation and quantification. The remediation of a contaminated site requires an optimal decision making system to identify the pollutant source characteristics accurately and efficiently. The source characteristics are generally identified using contaminant concentration measurements from arbitrary or planned monitoring locations. To effectively characterize the sources of pollution, the monitoring locations should be selected appropriately. An efficient monitoring network will result in satisfactory characterization of contaminant sources. On the other hand, an appropriate design of monitoring network requires reliable source characteristics. A coupled iterative sequential source identification and dynamic monitoring network design, improves substantially the accuracy of source identification model. This paper reviews different source identification and monitoring network design methods in groundwater contaminant sites. Further, the models for sequential integration of these two models are presented. The effective integration of source identification and dedicated monitoring network design models, distributed sources, parameter uncertainty, and pollutant geo-chemistry are some of the issues which need to be addressed in efficient, accurate and widely applicable methodologies for identification of unknown pollutant sources in contaminated aquifers.

Hydrogeological Study of the Aquifer System in Central Tunisia: New System Structuring of Horchane Aquifers

Hydrogeological investigations, tectonics and seismic reflection show the complexity of the Horchane groundwater and drainage possibilities with neighboring groundwater in central Tunisia. Seismic reflection lines intersecting the region show the role of halokinetic movements, by the intrusion along preexisting faults, in the restructuring of the hydrogeological basin. The salt domes associated with a chaotic facies at the base of outcrops, that limit the Horchane basin, puch to outcrops the areas of recharge area. Geoelectric section shows the anisotropy and the importance of Mio-Plio-Quaternary (MPQ) sediment along the gutters, between the outcrops of El Hafay and Kebar on the one hand, and outcrops of Kebar and Majoura on the other. These gutters are communicated with channels that facilitate drainage of the Horchane complex groundwater by that Gammouda in North-East and Braga in East. The results of this study clearly indicate the important role of the geology in the restructuring of groundwater basins, through early halokinetic movements. (i.e. halokinetic movements). The aquifer geometry is controlled by the ascent of Triassic salt material, from the Middle Jurassic, in central Tunisia.

Numerical simulation of dewatering thick unconsolidated aquifers for safety of underground coal mining

With an increase of mining the upper limits under unconsolidated aquifers, dewatering of the bottom aquifer of the Quaternary system has become a major method to avoid water and sand inrushes.In the 8th District of the Taiping Coal Mine in south-western Shandong province, the bottom aquifer of the Quaternary system is moderate to excellent in water-yielding capacity.The base rock above the coal seam is very thin in the concealed coal field of the Carboniferous and Permian systems.Therefore, a comprehensive dewatering plan from both the ground surface and the panel was proposed to lower the groundwater level in order to ensure mining safety.According to the hydrogeologic conditions of the 8th District, we established a numerical model so that we could simulate the groundwater flow in the dewatering process.We obtained the simulation parameters from previous data using backward modeling, such as the average coefficient of permeability of 12 m/d and the elastic storage coefficient of 0.002.From the same model, we predicted the movement of groundwater and water level variables and obtained the visible effect of the dewatering project.Despite the overburden failure during mining, no water and/or sand inrush occurred because the groundwater level in the bottom aquifer was lowered to a safe water level.

Hydrochemical characteristics of aquifers in Northern Gezira State,Central Sudan

This paper presents an assessment of the hydrochemical characteristics of groundwater in Northern Gezira State, Central Sudan. The approaches followed here include the chemical analyses for major ions chemistry and construction of hydrochemical maps of total dissolved solids (TDS), sodium (Na +), bicarbonate (HCO 3 -), and chloride (Cl -) ions. The hydrochemical characteristics of the groundwater in each aquifer and management consideration are discussed. Sources of major ions in groundwater are analyzed. The hydrochemical maps of important species are constructed. The relationship of groundwater to use is elaborated. High concentrations of the chemical and hydrochemical constituents and the occurrence of calcretes (CaCO 3) in upper zones suggest a long history of evaporation and increasing leachates.

Ground Subsidence in Areas of Loose Porous Aquifers

Groundwater is one of the important water resources in northern China's plain areas. Many severe geological hazards have occurred in these areas due to ground subsidence which is caused by over exploitation of groundwater. This paper introduces and analyses the ground subsidence caused by groundwater exploitation and its mechanism in the northern China's plains. A ground subsidence prediction model has been developed based on the consolidation theory. The authors have tested this model in a case study of Fuyang City, Anhui Province, where ground subsidence is a severe environmental problem. In the case study, the model results match very well with those of the actual measurement. Two schemes of groundwater exploitation are assessed. The conclusion from the study could be used in the long-term water and economical management planning. The strategies for the control of ground subsidence are discussed.

Hydrogeological Conceptual Model of Groundwater from Carbonate Aquifers Using Environmental Isotopes (¹⁸O, ²H) and Chemical Tracers: A Case Study in Southern Latium Region, Central Italy

The present work provides hydrochemical and stable isotope data and their interpretations for 54 springs and 20 wells, monitored from 2002 to 2006, in the Southern Latium region of Central Italy to identify flow paths, recharge areas and hydrochemical processes governing the evolution of groundwater in this region. The hydrogeological conceptual model of the carbonate aquifers of southern Latium was based on environmental isotopic and hydrochemical investigation techniques to characterize and model these aquifer systems with the aim of achieving proper management and protection of these important resources. Most of the spring samples, issuing from Lepini, Ausoni and Aurunci Mts., are characterized as Ca-Mg-HCO3 water type, however, some samples show a composition of Na-Cl and mixed Ca-Na-HCO3-Cl waters. Groundwater samples from Pontina Plain are mostly characterized by Na-Cl and Ca-Cl type waters. Geochemical modeling and saturation index computation of the Lepini, Ausoni Aurunci springs and Pontina Plain wells shows an interaction with carbonate rocks. Most of the spring and well water samples were saturated with respect to calcite and dolomite, however all sampled waters were undersaturated with respect to gypsum and halite. The relationship between δ18O and δ2H, for spring and well water samples, shows shifts of both the slope and the deuterium excess when compared to the world meteoric (WMWL) and central Italy meteoric (CIMWL) water lines. The deviation of data points from the meteoric lines can be attributed to evaporation both during the falling of the rain and by run-off on the ground surface before infiltration. Most springs and wells have a deuterium excess above 10 ‰ suggesting the precipitation in the groundwater comes from the Mediterranean sector. On the basis of local isotopic gradients, in combination with topographic and geologic criteria, four recharge areas were identified in the Aurunci Mountains. In Pontina Plain, the elevations of the recharging areas suggest that the Lepini carbonate aquifers are feeding them.

Uncertainty and Sensitivity Analyses of the Simulated Seawater—Freshwater Mixing Zones in Steady-State Coastal Aquifers

The uncertainty and sensitivity of predicted positions and thicknesses of seawater-freshwater mixing zones with respect to uncertainties of saturated hydraulic conductivity, porosity, molecular diffusivity, longitudinal and transverse dispersivities were investigated in both head-control and flux-control inland boundary systems. It shows that uncertainties and sensitivities of predicted results vary in different boundary systems. With the same designed matrix of uncertain factors in simulation experiments, the variance of predicted positions and thickness in the flux-control system is much larger than that predicted in the head-control system. In a head-control system, the most sensitive factors for the predicted position of the mixing zone are inland freshwater head and transverse dispersivity. However, the predicted position of the mixing zone is more sensitive to saturated hydraulic conductivity in a flux-control system. In a head-control system, the most sensitive factors for the predicted thickness of the mixing zone include transverse dispersivity, molecular diffusivity, porosity, and longitudinal dispersivity, but the predicted thickness is more sensitive to the saturated hydraulic conductivity in a flux-control system. These findings improve our understandings for the development of seawater-freshwater mixing zone during seawater intrusion processes, and give technical support for groundwater resource management in coastal aquifers.