“…Studies in Ghana and Burkina Faso have shown that the oxidation of arsenic-containing sulphide minerals found in rocks of the Birimian formation is the initial process responsible for high arsenic levels found in some groundwater (Asante et al, 2007;Barro-Traoré et al, 2008;Buamah et al, 2008;Sako et al, 2016;Smedley, 1996;Smedley et al, 2007;Somé et al, 2012). However, an understanding of the extent of the problem and a detailed investigation of the sources and geological conditions leading to arsenic contamination is currently lacking.…”
Arsenic contamination in groundwater from crystalline basement rocks in West Africa has only been documented in isolated areas and presents a serious health threat in a region already facing multiple challenges related to water quality and scarcity. We present a comprehensive dataset of arsenic concentrations from drinking water wells in rural Burkina Faso (n=1498), of which 14.6% are above 10μg/L. Included in this dataset are 269 new samples from regions where no published water quality data existed. We used multivariate logistic regression with arsenic measurements as calibration data and maps of geology and mineral deposits as independent predictor variables to create arsenic prediction models at concentration thresholds of 5, 10 and 50μg/L. These hazard maps delineate areas vulnerable to groundwater arsenic contamination in Burkina Faso. Bedrock composed of schists and volcanic rocks of the Birimian formation, potentially harbouring arsenic-containing sulphide minerals, has the highest probability of yielding groundwater arsenic concentrations >10μg/L. Combined with population density estimates, the arsenic prediction models indicate that ~560,000 people are potentially exposed to arsenic-contaminated groundwater in Burkina Faso. The same arsenic-bearing geological formations that are positive predictors for elevated arsenic concentrations in Burkina Faso also exist in neighbouring countries such as Mali, Ghana and Ivory Coast. This study's results are thus of transboundary relevance and can act as a trigger for targeted water quality surveys and mitigation efforts.
“…Studies in Ghana and Burkina Faso have shown that the oxidation of arsenic-containing sulphide minerals found in rocks of the Birimian formation is the initial process responsible for high arsenic levels found in some groundwater (Asante et al, 2007;Barro-Traoré et al, 2008;Buamah et al, 2008;Sako et al, 2016;Smedley, 1996;Smedley et al, 2007;Somé et al, 2012). However, an understanding of the extent of the problem and a detailed investigation of the sources and geological conditions leading to arsenic contamination is currently lacking.…”
Arsenic contamination in groundwater from crystalline basement rocks in West Africa has only been documented in isolated areas and presents a serious health threat in a region already facing multiple challenges related to water quality and scarcity. We present a comprehensive dataset of arsenic concentrations from drinking water wells in rural Burkina Faso (n=1498), of which 14.6% are above 10μg/L. Included in this dataset are 269 new samples from regions where no published water quality data existed. We used multivariate logistic regression with arsenic measurements as calibration data and maps of geology and mineral deposits as independent predictor variables to create arsenic prediction models at concentration thresholds of 5, 10 and 50μg/L. These hazard maps delineate areas vulnerable to groundwater arsenic contamination in Burkina Faso. Bedrock composed of schists and volcanic rocks of the Birimian formation, potentially harbouring arsenic-containing sulphide minerals, has the highest probability of yielding groundwater arsenic concentrations >10μg/L. Combined with population density estimates, the arsenic prediction models indicate that ~560,000 people are potentially exposed to arsenic-contaminated groundwater in Burkina Faso. The same arsenic-bearing geological formations that are positive predictors for elevated arsenic concentrations in Burkina Faso also exist in neighbouring countries such as Mali, Ghana and Ivory Coast. This study's results are thus of transboundary relevance and can act as a trigger for targeted water quality surveys and mitigation efforts.
“…In the present study, the Piper diagram of the seasonal distribution of major ions revealed four distinct water facies in the Passakongo's dug wells ( Figure 6). Thirteen water samples were classified as Ca-HCO 3 type and one sample as mixed Ca-Mg-Cl and another sample as Na-Cl type during the dry season, reflecting the predominant influence of water -rock interaction on the hydrogeochemical signature of the well water (Smedley et al, 2007;Mall et al, 2015;Sako et al, 2016;Rakotondrabe et al, 2017). The hydrochemical facies shifted from predominately Ca -HCO 3 type to mixed Ca-Na-HCO 3 (2 well), Na-HCO 3 (5 wells), Ca-Mg-Cl (2 wells), Ca-Cl (1 well) and Na-Cl (1 well) types during the wet period.…”
Section: Hydrogeochemical Evolution Of Dug Well Watermentioning
Hydrogeochemical characterization and suitability study of dug well water for domestic purpose were carried out in a semi-arid rural village in Burkina Faso. Thirty water samples were collected from 15 wells in dry and wet seasons, 2017. Electrical conductivity (EC) and total dissolved solids as well as major ions of all samples were within the World Health Organization (WHO) permissible limits for drinking water. In contrast, nine wells had pH beyond the WHO limit during the dry season and one well had very high NO3- concentration in the wet season. Most wells were seriously polluted with total Cr (CrT) in both seasons (11 and 14 wells in dry and wet seasons, respectively). Although Pb was not detected in the wells during the dry season, six wells showed Pb concentrations exceeding the WHO guideline limit for drinking water in the wet season. Graphic interpretation, including the Piper diagram, major ion ratios and Na/Cl versus EC, were used to characterize the hydrochemistry and water – rock interaction within the wells. The dominant hydrochemical facies of the wells was Ca-HCO3 during the dry season, reflecting the influence of silicate weathering. Following loadings of agricultural and domestic effluent, the hydrochemical facies shifted to more mixed type during the wet season. All samples had negative chloro-alkaline indices, suggesting retention of Ca2+ and Mg2+ by the aquifer materials and release of Na+ and K+ into the groundwater. In addition to silicate weathering, the hydrochemistry and water quality of the majority of the wells were partially controlled by the evaporation process and longer water–rock interaction in the dry season. In contrast, recharge and dilution effects appeared to alter the natural hydrochemistry of the wells in the wet season. Geochemical characterization has clearly shown that seasonal changes do affect the dug well water quality. The study also demonstrated that, in terms of CrT and Pb, water from the majority of the wells was not suitable for drinking. A special attention should be therefore paid to groundwater quality protection in the
“…An increasing number of people would rely on groundwater resources (Scanlon et al, 2006), the availability of which is an essential issue in drylands with relatively vulnerable water resources systems (Scanlon et al, 2009; Zhang & Dang, 2014). Aquifers obtain water via the process of groundwater recharge (Condon et al, 2020; Huang, Pang, et al, 2020), which also affects groundwater quality (Huang et al, 2013; Kim et al, 2005; Sako et al, 2016; Scanlon et al, 2007). Therefore, a reliable estimation of the recharge rate is of great significance for the assessment of groundwater quantity and quality.…”
The use of the sulphate mass balance (SMB) between precipitation and soil water as a supplementary method to estimate the diffuse recharge rate assumes that the sulphate in soil water originated entirely from atmospheric deposition; however, the origin of sulphate in soil and groundwater is often unclear, especially in loess aquifers.This study analysed the sulphur (δ 34 S-SO 4 ) and oxygen (δ 18 O-SO 4 ) isotopes of sulphate in precipitation, water-extractable soil water, and shallow groundwater samples and used these data along with hydrochemical data to determine the sources of sulphate in the thick unsaturated zone and groundwater of a loess aquifer. The results suggest that sulphate in groundwater mainly originated from old precipitation.When precipitation percolates through the unsaturated zone to recharge groundwater, sulphates were rarely dissolved due to the formation of CaCO 3 film on the surface of sulphate minerals. The water-extractable sulphate in the deep unsaturated zone (>10 m) was mainly derived from the dissolution of evaporite minerals and there was no oxidation of sulphide minerals during the extraction of soil water by elutriating soil samples with deionized water. The water-extractable concentration of SO 4 was not representative of the actual SO 4 concentration in mobile soil water.Therefore, the recharge rate cannot be estimated by the SMB method using the water-extractable concentration of SO 4 in the loess areas. This study is important for identifying sulphate sources and clarifying the proper method for estimating the recharge rate in loess aquifers. K E Y W O R D S groundwater recharge, loess tableland, sulphur and oxygen isotopes, unsaturated zone 1 | INTRODUCTION Drylands are distributed worldwide, which account for 45% of the global land area (Pr av alie, 2016) and 38% of the world's population lives in this area (Zhang & Dang, 2014). An increasing number of people would rely on groundwater resources (Scanlon et al., 2006
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