Assessment of Seawater Intrusion in Coastal Aquifers Using Multivariate Statistical Analyses and Hydrochemical Facies Evolution-Based Model

Groundwater (GW) studies have been conducted worldwide with regard to several pressures, including climate change, seawater intrusion, and water overexploitation. GW quality is a very important sector for several countries in the world, in particular for Tunisia. The shallow coastal aquifer of Sfax (located in Tunisia) was found to be under the combined conditions of continuous drop in GW and further deterioration of the groundwater quality (GWQ). This study was conducted to identify the processes that control GWQ mainly in relation to mineralization sources in the shallow Sfax coastal aquifer. To perform this task, 37 wells are considered. Data include 10 physico-chemical properties of groundwater analyzed in water samples: pH, EC, calcium (Ca), sodium (Na), magnesium (Mg), potassium (K), chloride (Cl), sulfate (SO4), bicarbonate (HCO3), and nitrate (NO3), i.e., investigation was based on a database of 370 observations. Principal component analysis (PCA) and hydrochemical facies evolution (HFE) were conducted to extract the main factors affecting GW chemistry. The results obtained using the PCA model show that GWQ is mainly controlled by either natural factors (rock–water interactions) or anthropogenic ones (agricultural and domestic activities). Indeed, the GW overexploitation generated not only the GWQ degradation but also the SWI. The inverse distance weighted (IDW) method, integrated in a geographic information system (GIS), is employed to achieve spatial mapping of seawater intrusion locations. Hydrochemical facies evolution (HFE) results corroborate the seawater intrusion and its spatial distribution. Furthermore, the mixing ratio showed that Jebeniana and Chaffar–Mahares localities are characterized by high SWI hazard. This research should be done to better manage GW resources and help to develop a suitable plan for the exploitation and protection of water resources.

Groundwater geochemistry and hydrogeochemical processes assessment in Bantul, Yogyakarta, Indonesia

In Bantul, Southern Yogyakarta, groundwater is the main source of domestic water needs. Therefore, knowing the hydrogeochemistry of groundwater is crucial in order to manage a sustainable groundwater resource. To characterize the compelling geochemical processes that control the groundwater chemistry, further hydrogeochemical examinations were directed in the area. Thirty groundwater samples were collected from shallow dug wells during the early dry season (April 2021). Sampling procedures and chemical analysis were carried out as per standard methods with secondary data obtained in 2006. The geochemical evaluations were depicted using several graphical plots dependent on the ionic constituents, hydrochemical facies, and controlling factors of groundwater quality. Two major hydrochemical facies were identified: alkaline-earth water with higher alkali; bicarbonate predominated (62%) and alkaline-earth water; bicarbonate predominated (32%). Weathering of silicate minerals occurs in 70% of recent samples and predominantly regulates major ion chemistry such as calcium, magnesium, sodium, and potassium. Chloro-alkaline indices 1,2 values signify that there are two potential rock-water interaction processes in the study region, namely the ion exchange and reverse ion exchange. Concentrations of nitrate, sulfate, and chloride indicate that the water chemistry has not been heavily contaminated by the land use in the area and is still mainly controlled by geogenic processes rather than anthropogenic activities.

Hydrogeochemical Characterization and Its Seasonal Changes of Groundwater Based on Self-Organizing Maps

Water resources are scarce in arid or semiarid areas; groundwater is an important water source to maintain residents’ lives and the social economy; and identifying the hydrogeochemical characteristics of groundwater and its seasonal changes is a prerequisite for sustainable use and protection of groundwater. This study takes the Hongjiannao Basin as an example, and the Piper diagram, the Gibbs diagram, the Gaillardet diagram, the Chlor-alkali index, the saturation index, and the ion ratio were used to analyze the hydrogeochemical characteristics of groundwater. Meanwhile, based on self-organizing maps (SOM), quantification error (QE), topological error (TE), and the K-means algorithm, groundwater chemical data analysis was carried out to explore its seasonal variability. The results show that (1) the formation of groundwater chemistry in the study area was controlled by water–rock interactions and cation exchange, and the hydrochemical facies were HCO3-Ca type, HCO3-Na type, and Cl-Na type. (2) Groundwater chemical composition was mainly controlled by silicate weathering and carbonate dissolution, and the dissolution of halite, gypsum, and fluorite dominated the contribution of ions, while most dolomite and calcite were in a precipitated state or were reactive minerals. (3) All groundwater samples in wet and dry seasons were divided into five clusters, and the hydrochemical facies of clusters 1, 2, and 3 were HCO3-Ca type; cluster 4 was HCO3-Na type; and cluster 5 was Cl-Na type. (4) Thirty samples changed in the same clusters, and the groundwater chemistry characteristics of nine samples showed obvious seasonal variability, while the seasonal changes of groundwater hydrogeochemical characteristics were not significant.

Evaluation of the Variability of Drinking Water Quality within Bamenda Metropolis, North West Region, Cameroon

Aims: The quality of drinking water within Bamenda metropolis was evaluated for it variability and suitability. Place and Duration of Study: Twenty-two (22) samples were collected (11 in the dry season and 11 in the wet season) from 4 main drinking water network in Bamenda (public, community, non-distributed and private network). Methodology: The samples were tested for physico-chemical and bacteriological parameters. American Society for Testing and Materials (ASTM) and Norme Française (NF) were the methods used to determine the organoleptic, natural structure, undesirable, toxic and bacteriological parameters of the different samples. Water Quality Index (WQI), Na/Cl ratio and hydrochemical facies were deduced from the physiochemical parameters. Results: The findings indicate that water quality in Bamenda varies with seasons, location and sources. The pH of the study area was acidic with a higher dry season mean percentage of 52.6% against 47.4% for wet season. Turbidity showed amean percentage of 75: 25% for wet and dry season respectively. Wet season cations, showed abundance Ca2+ and Mg2+ while dry season showed Ca2+ and Na+. Bicarbonate and Chloride were the most abundant anions in both seasons but varied with seasonal concentrations. Bacteriological analysis identified faecal coliform in 3 dry season samples. Hydrochemical facies showed dominant of magnesium and bicarbonate for wet season samples while Sodium and Chlorine were dominant for dry season samples. Water Quality Index (WQI) ranged from 72 to 94 for the wet season and 84 to 100 for dry season. Conclusion: Though the results for WQI were within the acceptable standard for drinking water, pH for 21 samples and turbidity of 6 samples were not within the Cameroon nor World Health Organisation (WHO) Standard for drinking water. It is important that drinking water be tested seasonally to ascertain the quality being consumed.

Origins And Processes of Groundwater Salinization Beneath Playa Lake Aquifers In Iran: A Chemical And Stable Isotope Approach

Groundwater salinization and interaction between Playa Lake and regional groundwater was investigated using multi-chemo-isotopic evidences. Forty groundwater and 26 Kashan Playa Lake (KPL) water samples collected and analyzed for their geochemical compositions. The evolution of hydrochemical facies in Kashan Plain Aquifer (KPA) to KPL is Ca-HCO3 (19%), Mix Ca-Cl (9%), Ca-Cl (17%), and Mix Na-Cl and Na-Cl (55%). Also, the Hydrochemical Facies Evolution Diagram (HFE-D) proposed cation exchange as the main process of salinization in KPA. Based on the binary hydrogeochemical diagrams of (Na+/ Cl-)/Cl-, (Ca2++Mg2+)/HCO3-+SO42-, and Cl/Br, dissolution of halite and gypsum in the Miocene marlstone in the KPA is the main source of salinity. The isotopic composition δ18O in aquifer and playa water samples varies from -10.03 to 7.03‰ (VSMOW) with an average of -6.95 ‰ and -60.73 to 25.08 ‰ with average of -45.82 ‰ for δ2H. Based on the result, the relation between δ18O and δ2H, and δ18O and Br, approve discharge of saline water from KPA to KPL. Likewise, the isotopic composition of δ34SO4, varies from 5.95 to 22.55 ‰ CDT in KPA, and 5.95 to 9.99 ‰ CDT in KPL. Also, the relation between δ18O- δ34SSO4 and Cl- δ34S were non-linear, indicating that sulphur concentration in KPA and KPL changed due to sulphide oxidation and sulphate reduction in the freshwater and deep brines in the aquifer and mixed during the over-pumping in the KPA. Oxidation of sulphide minerals such as galena (PbS), and Chalcopyrite (CuFeS2) may have been the source of sulfur in Dore mine in western part of the aquifer (recharge zone) leached by seasonal runoff. In general, water–rock interaction, ion exchange, and hydraulic gradient have been the dominating factors in changing the water chemistry between aquifer and playa leading to saline groundwater discharged to the playa.

Geothermal potential, chemical characteristic and utilization of groundwater in Serbia

In order to collect and unify data about all geothermal resources in Serbia, a database is formed. The database allows us to perceive the geothermal resources of Serbia and their potential for utilization. Based on the data available in the geothermal database, the estimated temperatures of reservoirs, heat power, and geothermal energy utilization were calculated. The database contains 293 objects (springs, boreholes) registered at 160 locations with groundwater temperature in the range between 20°C and 111°C. The maximum expected temperature of the reservoir is 146°C (according to the SiO2 geothermometer). Some thermal water is cooled while mixed with cold, shallow water. Geothermal resources are mostly used for balneology and recreation, and less for heating, water supply, bottling, fish and animal farms, agriculture, and technical water. 26% of all geothermal resources is used by the local population or has not been used at all. The annual utilization of geothermal energy for direct heat is 1507 TJ/yr, and the estimated capacity of geothermal energy in Serbia is 111 MWt. The results of analytical work were presented in the form of maps with a geological and hydrogeological background. Thermal waters are mostly registrated in the area of Tertiary magmatism. The three geothermal potential areas are identified: Pannonian basin-Vojvodina Province, Mačva-Srem and area from Jošanička Banja to Vranjska Banja (southern Serbia). Based on chemical analyses, four hydrochemical facies are distinguished. Thermal water mainly belongs to NaHCO3 or CaMgHCO3 hydrochemical facies, usually depending on the primary aquifer: karst, karst-fissured, intergranular or fissured.

The Contribution of Groundwater to the Salinization of Reservoir-Based Irrigation Systems

This study evaluates the cause of salinization in an irrigation scheme of 100 ha supplied from a reservoir. The scheme is located in Gumselasa catchment (28 km2), Tigray region, northern Ethiopia. The catchment is underlain by limestone–shale–marl intercalations with dolerite intrusion and some recent sediments. Water balance computation, hydrochemical analyses and irrigation water quality analyses methods were used in this investigation. Surface waters (river and reservoir) and groundwater samples were collected and analyzed. The water table in the irrigated land is ranging 0.2–2 m below the ground level. The majority of groundwater in the effective watershed area and the river and dam waters are fresh and alkaline whereas in the command area the groundwater is dominantly brackish and alkaline. The main hydrochemical facies in the groundwater in the effective watershed area are Ca-Na-SO4-HCO3, Ca-Na- HCO3-SO4, and Ca-Na-Mg-SO4-HCO3. The river and dam waters are Mg-Na-HCO3-SO4 and HCO3-SO4-Cl types, respectively. In the command area the main hydrochemical facies in the groundwater are Ca-Na-HCO3-SO4 and Ca-Na-Mg-SO4-HCO3. Irrigation water quality analyses revealed that salinity and toxicity hazards increase from the effective watershed to the irrigated land following the direction of the water flow. The results also showed that the analyzed waters for irrigation purpose had no sodicity hazard. The major composition controlling mechanisms in the groundwater chemistry was identified as the dissolution of carbonate minerals, silicate weathering, and cation exchange. One of the impacts of the construction of the dam in the hydrologic environment of the catchment is on its groundwater potential. The dam is indirectly recharging the aquifers and enhances the groundwater potential of the area. This increment of availability of groundwater enhanced dissolution of carbonate minerals (calcite, dolomite, and gypsum), silicate weathering and cation exchange processes, which are the main causes of salinity in the irrigated land. The rising of the brackish groundwater combined with insufficient leaching contributed to secondary salinization development in the irrigated land. Installation of surface and subsurface drainage systems and planting salt tolerant (salt loving) plants are recommended to minimize the risk of salinization and salt accumulation in the soils of the irrigated land.

Assessment of river water–groundwater–seawater interactions in the coastal delta of Bangladesh based on hydrochemistry and salinity distribution

A synchronization study among hydrochemistry, hydrochemical facies evaluation, EC observation, salinity distribution and groundwater flow direction has been addressed to assess river water–groundwater–seawater interactions in the coastal delta of southern Bangladesh. The findings show that river water, shallow groundwater and deep groundwater interact with seawater at various intensities within the complex dynamics of hydrochemical facies evaluation. Deep groundwater is intensively influenced by seawater, where shallow groundwater is moderately affected and river water is very negligibly affected. Major cation and anion have been plotted in the Piper diagrams and hydrochemical facies diagrams (HFE-D) to clarify the result. More than 60% of the water samples of the river lie on the Ca-HCO3 (or Mg-HCO3) facies quadrant, and more than 70% of the shallow groundwater samples and more than 95% of the deep groundwater samples lie on the Na-Cl facies quadrant of the HFE-D diagram. River water types are dissimilar, and approximately 82% of facies are characterized by freshening phases and 18% by intrusion phases. Mixed water types with predominate of Na-Cl were observed in shallow groundwater where the hydrochemical facies are characterized by 53 percent freshening phases and 47 percent intrusion phases. Deep groundwater hydrochemistry clearly indicates the dominant Na-Cl type of water in the study area where only four hydrochemical facies are observed and 78 percent correspond to the intrusion phases and 22 percent to the freshening phases. Both direct and reverse cation exchange reactions take place in shallow groundwater, where deep groundwater is predominantly characterized by reverse cation exchange reactions. Two end members: seawater of Bay of Bengal and freshwater, contribute to the exchange reactions in the coastal aquifer of the study area. In terms of nitrate contamination, river waters are affected by negligible to low concentrations, shallow groundwater is affected by moderate to high concentrations and deep groundwater is affected by moderate to very high nitrate concentrations. Dissimilarity in electrical conductivity (EC) values, variation of salinity distribution maps and groundwater flow direction suggest the possible interconnections among river water, groundwater and aquifer sediments. Significant concentrations of Na+ and Cl− ions lead to seawater contamination in groundwater, and HCO3− along with Na+, Ca2+, Mg2+ in river water suggests mixing of freshwater and seawater, which could have adverse effects both in coastal delta aquatic life and in agriculture.