Seyni Ndoye

The Quaternary sand aquifer of the Samba Dia lens is a critically important water reserve for the municipalities of Fimela, Djilass, and Diofior, located near the Atlantic Ocean and hypersaline waters of the Saloum estuary in central-western Senegal. To assess the influence of this environment on groundwater quality, two water sampling campaigns were carried out in March 2021 and January 2024 on 33 wells. The objective of this study is to evaluate the evolution of groundwater chemical quality during this period. Data interpretation was performed using a multidisciplinary approach based on descriptive statistics of physicochemical parameters, identification of chemical facies using Piper's diagram, analysis of the mineralization process, the use of the hydrochemical facies evolution diagram (HFE-D) to measure the impact of recharge and basic ion exchange processes, and Stuyfzand classification to identify water types. A study of the suitability of water for various uses was also conducted to assess the evolution of water suitability between the two periods. The results indicate that this aquifer consists mainly of chloride facies. Four facies were identified in 2021: NaCl (72.72%), CaCl (12.12%), CaHCO ₃ (9.09%) and NaHCO ₃ (6.07%) increasing to five in 2024: NaCl (66.66%), CaHCO ₃ (24.24%), NaHCO ₃ (3.03%), CaCl (3.03%), MgCl (3.03%) with the emergence of a new magnesian facies. This evolution is marked by a generalized increase in seawater intrusion, which rises from 33.33% in 2021 to 66.66% in 2024. Several wells located in the center of the area, which were characterized in 2021 by a softening process, find themselves under the influence of saline water intrusion after three years. The Stuyzand classification indicates an increase in the representativeness of salt water in the aquifer, varying from 24.24% to 30.30% over three years. However, the suitability of the water for drinking and irrigation is not yet affected by the increase in salinity. This widespread increase in water salinity is the result of saltwater intrusion due to excessive pumping of the Quaternary aquifer, leaching of saline soils from the surface in coastal areas, reduced recharge in the center between the two periods, and a reverse ion exchange process in which Ca ²⁺ and Mg ²⁺ ions replace Na ⁺ ions.

This study provides a detailed assessment of groundwater salinization in the Quaternary aquifer of the Samba Dia region, Senegal, using an integrated approach that combines hydrochemical, stable isotopic (δ²H, δ¹⁸O), and electrical resistivity tomography (ERT) techniques. Fourteen high-resolution ERT profiles, along with comprehensive chemical and isotopic analyses, were performed to identify the main causes of salinity and their spatial distribution. Results show that groundwater salinization in the area is primarily driven by three mechanisms: seawater intrusion, surface salt leaching, and ion exchange. Hydrochemical facies evolution diagrams, ionic ratios, and isotopic signatures helped differentiate marine-influenced zones from inland salinization areas. ERT imaging also mapped the three-dimensional extent and geometry of saline interfaces, confirming zone-specific mixing of seawater and freshwater. The findings indicate that salinization of the coastal aquifer has worsened over the past twenty years, mainly due to human activities and climate variability. This study recommends a sustainable monitoring strategy to support aquifer management, focusing on accurately identifying vulnerable zones and enabling adaptive resource planning in semi-arid Senegal.

A wastewater treatment plant (WWTP) prototype coupled with Moringa oleifera seeds (MOSs) was developed to evaluate its effectiveness to reduce metallic trace elements (MTEs) in domestic wastewater. The WWTP is composed of a septic tank (F0) where wastewater is treated by biological processes under anaerobic conditions, followed by a bacterial filter (F1) where wastewater is filtered under aerobic conditions, followed by an infiltration well (F2), which provides additional filtration of wastewater before discharge into the soil. MTEs present in waters can bind with humic substances contained in colloid particles and then be eliminated by coagulation–flocculation with a cationic polyelectrolyte. MOSs contain positively charged cationic polymers that can neutralize the colloids contained in waters, which are negatively charged. Based on this observation, 300 mg·L⁻¹ of MOS was added into F0, 50 mg·L⁻¹ into F1, and 50 mg·L⁻¹ into F2 mg·L⁻¹. MOS activation in samples was performed by stirring rapidly for 1.5 min, followed by 5 min of gentle stirring and 3 h of settling. The data analysis shows that wastewater samples had significant concentrations of MTEs, particularly for Cu, Ni, Sr, and Ti, and sediment samples had high amounts of Cr, Cu, Ni, Sr, Ti, and V. The addition of MOS to F0, F1, and F2 samples resulted in reductions in MTE concentration of up to 36%, 71%, 71%, 29%, 93%, 81%, 13%, 52%, and 67% for Co, Cr, Cu, Ni, Pb, Se, Sr, Ti, and V, respectively. The quantified MTEs (As, Co, Cr, Cu, Ni, Pb, Se and V) in treated samples were reported to be lower than UN-EP standards for a safe reuse for irrigation and MOS proved to be as effective as chemical coagulants such as lime and ferric iron for the removal of MTEs contained in wastewater. These results highlight the potential of MOSs as natural coagulants for reducing MTE content in domestic wastewater. This study could be the first to evaluate the effectiveness of MOS in reducing 10 MTEs, including As, Co, Se, Sr, Ti, and V, which are currently understudied. It could also provide a better understanding of the origin of MTEs found in domestic wastewaters and how an effective treatment process can result in high-quality treated wastewaters that can be reused for irrigation without posing health or environmental risks. However, more research on MOSs is needed to determine the type and composition of the coagulant substance found in the seeds, as well as the many mechanisms involved in the decrease in MTEs by MOSs, which is currently understudied. A better understanding of MOS structure is required to determine the optimum alternative for ensuring the optimal effect of MOS paired with WWTP in removing MTEs from domestic wastewaters.

Groundwater has been the main resource used for drinking, domestic and agricultural activities in West central Senegal for the past few decades. Thus, this study investigates the quality of groundwater and assesses its suitability for drinking and irrigation purposes. To this end, 42 samples were collected and analyzed for various chemical parameters (major ions, fluoride, pH, total dissolved solids (TDS)). Chemical data were interpreted using water quality indexes, Wilcox and USSL salinity diagrams, bivariate plots, ionic ratios and by comparing with the WHO standards. Results indicated that the groundwater is neutral to slightly alkaline with pH values between 7.1 and 8.2. Piper diagram shows that mixte-Ca-Na-Mg-HCO₃ is the dominant hydrochemical facies. TDS and water quality index (WQI) values indicated respectively that 69% and 64.3% of samples were suitable for drinking. Moreover, major ions concentrations were found below the desirable limits in most of groundwater samples. However, for fluoride, 69% of samples exceed the WHO guideline, limiting their use for drinking. The computed index of irrigation water quality and Wilcox diagram reveal that 87% and 78% of samples belong, respectively, to excellent to good category and excellent to good and good to permissible. Similarly, according to the US salinity classification, the majority of samples were acceptable for irrigation. Gibbs plots illustrate that water-rocks interaction with some extent evaporation is the main hydrochemical process controlling groundwater chemistry while bivariate plots and ionic ratios indicate that mineral dissolution and ion exchange play important role in groundwater chemistry.

Senegal central regions face rainfall deficit combined with scarcity of surface water and poor quality. Populations use groundwater for drinking and irrigation. A Groundwater assessment studiebased on 42 samples aims to determine their quality. Several parameters (TDS, TH, WQI, SAR, RSC, %N, PI, KR and MR) and ion chemistry determined . Samples exhibit an alcaline pH (7.6) and hydrochemical facies mainly Ca-Na-Mg-HCO3. The ionic dominance is Na+ ˃ Ca2+ ˃ Mg2+ ˃ K+ and HCO3- ˃ Cl- ˃ SO42- ˃ NO3- ˃ F-. From TDS and WQI index most of the groundwaters are suitable for drinking. Irrigation quality (based on SAR, %N, RSC, KR, MR) varie from excellent to good water type. Plotting chemical data (USSL salinity & Wilcox diagrams) reveals that the majority of the groundwater samples belong to the fields excellent to good and from good to permissible . Natural processes (rock weathering, mineral dissolution, evaporation and ion exchange) control groundwater quality. As the region faced a persistent rainfall deficit combine with fragile groundwater quality should alert the stakeholders. A sustainable development of the region can be faced if strong measures are planned to follow water quality evolution and quantity available for human purposes

Hydrogeochemical analyses were conducted on groundwater sampled from the Saloum aquifer, in southern Senegal. The objective was to identify the chemical processes that control hydrochemistry and to assess the quality of groundwater for determining its suitability for drinking and agricultural purposes. Water samples were collected from 79 wells during the dry season in May 2012, and were subjected to analysis for chemical characteristics (major ions), pH, electrical conductivity (EC) and total dissolved solid (TDS). The dominant hydrochemical facies observed for the groundwater samples are NaCl and CaHCO₃. Gibbs plot depicts predominance of rock water interaction and evaporation processes controlling the water chemistry. Percentage of Na⁺, Residual Sodium Carbonate (RSC), Total Hardness (TH) and Sodium Adsorption Ratio (SAR) values were calculated. The results were compared with the standard guideline values recommended by the World Health Organization and agricultural water standards. The TDS in groundwater is less than 1200 mg/L and SAR values are less than 10. RSC values overall are less than 1.25 meq/L. Results show that the groundwater in the area has generally a low hardness and is fresh (95%) to brackish. The majority of groundwater samples are appropriate for domestic uses. The indexes for water irrigation compared with standard limits revealed that most of the Saloum groundwater samples fall in the suitable range for irrigation.