Geochemical & Groundwater Studies

This study presents a comprehensive hydrochemical investigation of the multi-layered coastal aquifer system in the Great Maputo Area, Mozambique, to characterize the complex interactions between groundwater quality, recharge dynamics, and saltwater intrusion. Utilizing PHREEQC modeling with chemical diagnostics, the research evaluated the electroneutrality of 21 water samples, identifying analytical errors exceeding 5% in eight cases and necessitating specific bicarbonate corrections for the lake water proxy (Sample 60) to achieve an Electrical Balance (EB) of 0%.

Hydrochemical facies classification via the Stuyfzand scheme and Piper diagrams revealed a predominant transition from fresh calcium-bicarbonate waters to brackish sodium-chloride types, with Gibbs diagrams confirming that while interior geochemistry is driven by silicate and carbonate weathering, coastal zones are heavily influenced by intensive evaporation and cation exchange.

Using stable isotope analysis ( and ) and the Chloride Mass Balance (CMB) method—with Sample 60 serving as a rainwater proxy ( = 8.2 mg/L)—groundwater recharge was estimated to range from 0.4% to 75.4% of annual rainfall, with the highest infiltration rates occurring in low-elevation alluvial shrublands. Redox analysis further identified highly reduced conditions in specific samples, marked by elevated Fe²⁺ and depleted NO₃⁻, while widespread Manganese concentrations exceeding 0.08 mg/L highlight significant drinking water quality concerns. Ultimately, the integration of Cl/Br ratios and seawater mixing fractions demonstrates that regional water security is increasingly compromised by a combination of marine fingerprints, mineral dissolution, and anthropogenic influences, necessitating robust management strategies to mitigate salinization and contamination risks.

This study characterizes the hydrogeological and geochemical dynamics of the 9.08 km² Sole Catchment in Digne, France, to evaluate water flow pathways and the regional water balance. Utilizing a multi-disciplinary approach, the research integrated high-resolution discharge monitoring, lysimeter-based evapotranspiration measurements, and geophysical Vertical Electrical Soundings (VES) to delineate the subsurface architecture.

Geochemical analysis, interpreted through Stuyfzand classification, identified a transition between oligohaline-fresh Ca-HCO₃ and Ca-SO₄ water types, with alkalinity levels (145.2–461.3 mg/L) reflecting the dominant dissolution of Jurassic marl-limestone and Quaternary alluvial deposits. Piper diagram analysis confirmed that while the geochemistry is primarily lithogenically driven, specific trends in Electrical Conductivity (EC) and pH at the catchment outlet reveal significant anthropogenic influences from agricultural irrigation and wastewater treatment plant (WWTP) inflows.

Hydrological monitoring during the May 2023 period indicated a highly dynamic system, with Actual Evapotranspiration (AET) rates of 6.15 to 11.55 mm/day driving substantial short-term storage fluctuations (-106,076 to 39,460.8 m³). Geophysical surveys at the outlet identified thick, low-resistivity alluvial layers, suggesting significant untapped groundwater potential for drought resilience. However, the prevalence of disused wells and the close hydraulic connectivity between surface and groundwater indicate high vulnerability to contamination. The study concludes that while the alluvial aquifer is a vital strategic reserve, sustainable management requires long-term monitoring to bridge data gaps in groundwater-surface water interactions and anthropogenic mass balances.

This study investigates groundwater chemistry and contaminant transport processes in the urban environment of Arusha, Tanzania, using PHREEQC simulations to analyze ion balance, electrical conductivity, mineral saturation, and pollutant degradation pathways. Water samples from a local dug well were analyzed for key physicochemical parameters, including pH, alkalinity, major cations and anions, and microbial contaminants, with PHREEQC calculations indicating an ion balance error of 0.08% and an electrical conductivity of 1633 µS/cm, closely matching the measured value of 1600 µS/cm, confirming calcite precipitation due to supersaturation. The environmental fate of sulfamethoxazole (SMX), a commonly detected antibiotic, was explored, with expected groundwater metabolites under aerobic conditions identified as 4-aminobenzolsulfonate and 3-amino-5-methyl-isoxazole. Additionally, a 1D transport model was developed to simulate septic wastewater infiltration over 50 years in the Sombetini neighborhood, highlighting key geochemical processes such as pyrite oxidation, nitrate reduction, and iron mobilization, where pyrite reactivity intensified beyond 25 meters, generating Fe²⁺ and SO₄²⁻ as nitrate concentrations declined. Findings demonstrate that nitrate contamination from onsite sanitation significantly impacts aquifer chemistry, reinforcing the need for improved wastewater management strategies to mitigate water quality degradation, while controlled wastewater infiltration approaches could aid in nitrate reduction via pyrite interactions, supporting sustainable groundwater resource management and policy development for groundwater protection in urbanizing regions.

This study examines the geo-electrical characteristics of groundwater formations in Breevenen, Netherlands, aiming to interpret subsurface lithological variability and aquifer potential. Borehole data were grouped and schematised into lithological logs for integration with geo-electrical Vertical Electrical Sounding (VES) measurements. West-East and South-West to North-East cross-sections reveal connections between fine sand, coarse sand, and clay layers, contributing to aquifer identification. Resistivity interpretations highlight saline marine clays within the Breda formation as critical features influencing aquitard properties. Calibration tables of formation and pore-water resistivities enabled detailed classification of rock types and water content, distinguishing freshwater from saline zones. The study underscores the importance of accurate geo-electrical analysis for groundwater resource management in complex lithologies.

This study explores variable-density groundwater flow modeling using SEAWAT to simulate saline-freshwater interactions in coastal and island aquifers under various hydrogeological scenarios. It evaluates the performance of different advection solvers, examines the effects of parameters such as dispersion, density variation, and freshwater inflow reduction, and determines sustainable groundwater extraction rates to prevent saline upconing. Analytical and numerical solutions are compared to assess model accuracy, and measures like artificial recharge and saltwater barriers are proposed to improve coastal aquifer management. Real-world cases, including Henry's and Elder's benchmarks, illustrate saltwater intrusion dynamics and mitigation strategies, highlighting SEAWAT's utility in groundwater quality analysis and sustainable resource planning.

Assisted in MSc thesis work of Md. Nazrul Islam, under the supervision of Dr. Shyamal Karmakar, Associate Professor, IFESCU.

Abstract

Assessment of heavy metal loads in the Karnaphuli upstream water was carried out in the present study for Iron (Fe), Cadmium (Cd), Chromium (Cr), Copper (Cu), Nickel (Ni), Lead (Pb), Zinc (Zn), and Arsenic (As). The main objective of the investigation was to assess the heavy metal concentrations and understand geogenic reactions. The highest concentrations of the heavy metals in the water samples were found to be 1.869 mg/l for Fe, 0.417 mg/l for Zn, 0.245 mg/l for Cr, 0.086 mg/l for Cu, 0.034 mg/l for Ni, and 0.010 mg/l for Arabunia, Kolabunia, Subolong Bazar, Borodham, Near Circle waterfall, and Borodham areas, respectively. The highest concentrations of heavy metals in sediment samples were found to be 6.187 μg/g for Fe, 1.932 μg/g for Zn, 1.713 μg/g for Ni, 1.296 μg/g for Cu, 1.095 μg/g for Cr, and 0.009 μg/g for Cd. The mean values of the heavy metal loads in water were found to be 1.023 mg/l for Fe, 0.167 mg/l for Zn, 0.020 mg/l for Ni, 0.019 mg/l for Cu, 0.019 mg/l for Cr, and 0.006 mg/l for Cd. The mean concentrations of the heavy metals in the sediment samples were found to be 5.397 μg/g for Fe, 1.351 μg/g for Zn, 1.002 μg/g for Ni, 0.809 μg/g for Cu, 0.632 μg/g for Cr, and 0.007 μg/g for Cd. According to the concentration order of metal ions in water, they were Fe > Zn > Ni > Cu > Cd > Cr, and in sediment, they were Fe > Zn > Ni > Cu > Cr > Cd. Significant variations were found among stations for all heavy metals except Cd in water and sediment. The mean values of Fe, Zn, Ni, Cu, Cd, and Cr were found to be lower than the prescribed standard values for the safe limit of heavy metals in surface water. Conversely, Cu, Ni, Zn, and Cr were found to be higher than the recommended value for riverbed sediment, as per ECR 1997 and WHO Standard 2004. The concentrations of As and Pb were not detected by the atomic adsorption spectrophotometer, which suggests these metal ions were below the detection limit in the study area.