Evaluation of Water Resources Quality in Sabodala Gold Mining Region and Its Surrounding Area (Senegal)

peer reviewedGeochemical and Geostatistical tools were used to assess: 1) the chemical quality and, geochemical processes in crystalline rock aquifers in Sabodala (Eastern Senegal) and its surroundings and 2) the impact of mining activities on their quality. A total of 26 water samples collected at boreholes, dug wells and stream, were analyzed to determine major and trace elements concentration focused on elements that represent more threats on human health. Boxplots define chemical characteristics of water for each aquifer formation compared to surface waters. Geostatistical analysis show two sources of water mineralization with regard to major elements: a first natural source characterized by Ca-Mg-HCO3 water type from boreholes and unpolluted surface water and a second group characterized by polluted water by nitrates with Na-NO3-Cl type mainly observed in upper weathered aquifers. However, considering trace element, geostatistical analysis showed three water groups: water with very low trace element concentrations encountered in boreholes and unpolluted surface waters, and waters with relatively high trace element concentrations such as Al observed in areas affected by gold mining activities and finally, polluted waters by Ni, Co, Mn and Cr observed at Sabodala. Results show that in eastern Senegal well waters are vulnerable and often affected by pollution

Hydrogeological characterization and hydrodynamic behaviour of the overexploited Diass aquifer system (Senegal) inferred from long term groundwater level monitoring

peer reviewedDakar, the Capital city of Senegal concentrates about 23.2% (about 3 millions inhabitants) of the total population and a large proportion of the industrial activities. Water supply is ensured by surface water pumped and piped from the Guiers Lake (250 km distant from the capital) and from groundwater resources. Among these latter, the Diass aquifer system contributes to a substantial proportion (31% in 2019) of the total water supply distribution due to growing demand induced by the rapid demographic growth (about 2.5%). The Diass horst aquifer system located 50 km east of Dakar (Senegal) is exploited with two main aquifers covered by a sandy superficial aquifer: the confined/unconfined Palaeocene karstic limestone and the confined Maastrichtian sandstone aquifer underneath. This system has experienced intensive groundwater abstraction during the last 60 years to meet the increasing water demand. Abstraction for urban drinking water occurs in nine pumping fields with a rate reaching 174,000 m3/d in 2019. This high yield together with the drought conditions since the 1970s is likely to affect groundwater imbalance and change the flow regime. The objective of the study is to improve our understanding of the system dynamic with regards to the high pumping rate in order to build a conceptual scheme for further hydrogeological modeling of the system. In this study, we use monitored pumping rates, piezometric level from 1960s to 2019 and rainfall data from 1931 to December 2016 together with the hydrogeological configuration to infer the dynamics of the aquifer system. The high abstraction rate during the period 1958-2019 which vary from 16,000 to 174,000 m3/d has caused a continuous groundwater level decline (up to 30 m), a modification of the flow patterns and to some extent a quality deterioration through salinization processes as shown in a few boreholes in Sébikotane and Mbour. The piezometric levels which were above the sea level prior 1959 exhibit now negative values and can even reach -40 m in the vicinity of the pumping fields creating therefore piezometric depressions and convergent flow pattern. The hydrodynamic of the system derived from the results show that the reservoir acts as a multilayer aquifer system with interconnected compartments by faults that allow flux exchanges except the confining Ponty and Sébikotane faults. Overexploitation inducing important drawdown has induced an increase of the drainance fluxes between those different compartments. In order to foster more appropriate and sustainable groundwater abstraction in the complex hydrogeological system with regards to demand and water quality conservation, it is important to assess the main system behavior

Evaluation of Water Resources Quality in Sabodala Gold Mining Region and Its Surrounding Area (Senegal)

Geochemical and Geostatistical tools were used to assess: 1) the chemical quality and, geochemical processes in crystalline rock aquifers in Sabodala (Eastern Senegal) and its surroundings and 2) the impact of mining activities on their quality. A total of 26 water samples collected at boreholes, dug wells and stream, were analyzed to determine major and trace elements concentration fo-cused on elements that represent more threats on human health. Boxplots define chemical cha-racteristics of water for each aquifer formation compared to surface waters. Geostatistical analy-sis show two sources of water mineralization with regard to major elements: a first natural source characterized by Ca-Mg-HCO3 water type from boreholes and unpolluted surface water and a second group characterized by polluted water by nitrates with Na-NO3-Cl type mainly observed in upper weathered aquifers. However, considering trace element, geostatistical analysis showed three water groups: water with very low trace element concentrations encountered in boreholes and unpolluted surface waters, and waters with relatively high trace element concentrations such as Al observed in areas affected by gold mining activities and finally, polluted waters by Ni, Co, M

Evaluation of the LumiraDx SARS-CoV-2 antigen assay for large-scale population testing in Senegal

Purpose: Real-time reverse-transcription polymerase chain reaction (RT-PCR)-based testing remains the gold standard for the diagnosis of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Due to the high diagnosis demand of SARS-CoV-2 and the limited resources for RT-PCR testing, especially in Low-Income Countries (LICs), antigen-based methods are being considered as an option. The aim of this study was to assess the performance of LumiraDx SARS-CoV-2 antigen assay for large population screening compared to RT-PCR.Methods: This evaluation was conducted on 4146 participants including travelers and participants under household survey and vaccine evaluation studies before injection of the first dose. Oropharyngeal and nasopharyngeal swaps were collected from each participant into 2 mL of viral transport medium (VTM) and 400 μl of VTM were used to assess the performance of LumiraDx SARS-CoV-2 antigen assay, compared to RT-PCR. Results: The prevalence of SARS-CoV-2 of the cohort was 4.5% with RT-PCR and 4.1% with LumiraDx antigen test. Compared to the RT-PCR, the sensitivity and specificity of the LumiraDx antigen SARS-CoV-2 test were 82,7% [95% CI 74.1-89,7] and 99.9% [95% CI 99.6-99.9] respectively. Given the RT-PCR threshold cycle (Ct) range, the sensitivity was 92.1% [95% CI 84.6-96.3] when the Ct value was below or equal 33 cycles, and 38.1% [95% CI 18.9-61.3] when it was above 33 cycles. The inter-rater reliability showed a kappa coefficient of 0.88 when considering all the patients and 0.94 for Ct values below 33 cycles. Conclusion: Our data have shown that the LumiraDx platform can be considered for large-scale testing of SARS-CoV-2