Journal of Water, Sanitation and Hygiene for Development, 2020
In rapidly urbanising low-income towns and cities, there remains an absence of scientific evidenc... more In rapidly urbanising low-income towns and cities, there remains an absence of scientific evidence and regulatory structures to sustain the quality and quantity of groundwater used for low-cost water supplies and to reconcile this with continued use of the subsurface for low-cost sanitation. Here, we analyse the relationship between the density of on-site sanitation and shallow groundwater quality in the Thiaroye aquifer of Quaternary sands in Dakar, Senegal. On-site sanitation was mapped using object-oriented classification and visual interpretation of high-resolution, optical satellite images and ground-truthing surveys. Groundwater quality was assessed over a three-year period (2017–2019) from a network of 61 sources comprising boreholes, dug-wells, hand tubewells and piezometers. More than 253,000 on-site sanitation facilities are identified over an area of 520 km2 with densities ranging from 1 to 70 per hectare. A moderate, statistically significant linear relationship (r2 = 0....
Two billion people still consume drinking water contaminated with faeces. To improve this situati... more Two billion people still consume drinking water contaminated with faeces. To improve this situation, it has been recognised by UNICEF and the WHO that a more rapid approach to detecting faecally contaminated drinking water is necessary. We have previously demonstrated that fluorescence spectroscopy is a significant real-time indicator of the presence/absence and number of faecal indicator bacteria in drinking waters in low-income countries of the tropics. We have also established its potential as an online indicator of faecal contamination of public water supplies in the UK. Outstanding questions remain, however, over the source of the fluorescence and its uniqueness to faecal-indicator bacteria. To address these, we sampled potable groundwater supplies in Kenya, Malawi, Senegal and Uganda across an urbanisation transect from rural Malawi through to the city of Dakar (Senegal) where pollution sources and pressures vary considerably. We report on whether the fluorescence signal in th...
Fluorescent natural organic matter at tryptophan-like (TLF) and humic-like fluorescence (HLF) pea... more Fluorescent natural organic matter at tryptophan-like (TLF) and humic-like fluorescence (HLF) peaks is associated with the presence and enumeration of faecal indicator bacteria in groundwater. We hypothesise, however, that it is predominantly extracellular material that fluoresces at these wavelengths, not bacterial cells. We quantified total (unfiltered) and extracellular (filtered at < 0.22 µm) TLF and HLF in 140 groundwater sources across a range of urban population densities in Kenya, Malawi, Senegal, and Uganda. Where changes in fluorescence occurred following filtration they were correlated with potential controlling variables. A significant reduction in TLF following filtration (ΔTLF) was observed across the entire dataset, although the majority of the signal remained and thus considered extracellular (median 96.9%). ΔTLF was only significant in more urbanised study areas where TLF was greatest. Beneath Dakar, Senegal, ΔTLF was significantly correlated to total bacterial c...
All in-text references underlined in blue are linked to publications on ResearchGate, letting you... more All in-text references underlined in blue are linked to publications on ResearchGate, letting you access and read them immediately.
Schriftenreihe des Vereins fur Wasser-, Boden- und Lufthygiene, 2000
Dakar is a peninsula inhabited by a population of about 2 million people in 1996. In some dug wel... more Dakar is a peninsula inhabited by a population of about 2 million people in 1996. In some dug wells and piezometers, the nitrate content (NO3.) in the groundwater is above the World Health Organization (WHO) limit of 50 mg/l. In the unconfined part of the aquifer of the peninsula, all the samples from wells are contaminated by high nitrate contents which increased over time from 100 mg/l in 1987 to more than 250 mg/l in 1996. Only a limited area is affected by nitrate pollution in the confined layer. The results indicate anthropogenic pollution, a fact which indicates the increasing risk of pollution of drinking-water resources. Studies in the unsaturated zone and familiarity with the sanitation practices in the area indicate that the horizontal and vertical flux are linked mainly to defective septic tanks and direct organic waste elimination into the soil by more than 40% of the inhabitants. The correlation between tritium values (3H) and nitrate shows that the source of nitrate is...
Meeting: International Conference on Advances in Ground Water Hydrology, 16-19 Nov. 1988, Tampa, ... more Meeting: International Conference on Advances in Ground Water Hydrology, 16-19 Nov. 1988, Tampa, Fla., US
This study intends to see the temporal and spatial evolution of groundwater salinization at the n... more This study intends to see the temporal and spatial evolution of groundwater salinization at the northern and western zone of the CT aquifer in the Sine-Gambie region (Senegal). To do this, a hydrochemical study was conducted in 2015 and compared with previous studies (2000 and 2012). This study is essentially based on the two parameters, electrical conductivity and chloride content. The results obtained show that the evolution of salinity observed in these areas is explained by a contamination of the groundwater by the waters from the Saloum River and the sea. The comparison of groundwater electrical conductivity maps showed a salinity increase between 2000 and 2015; with a salinization phenomenon which increases toward inland in phase with chloride levels that doubled in some wells. The study also shows that several calcium bicarbonate facies have evolved to calcium chloride facies, and calcium chloride facies to chloride sodium facies.
Journal of Water, Sanitation and Hygiene for Development, 2020
In rapidly urbanising low-income towns and cities, there remains an absence of scientific evidenc... more In rapidly urbanising low-income towns and cities, there remains an absence of scientific evidence and regulatory structures to sustain the quality and quantity of groundwater used for low-cost water supplies and to reconcile this with continued use of the subsurface for low-cost sanitation. Here, we analyse the relationship between the density of on-site sanitation and shallow groundwater quality in the Thiaroye aquifer of Quaternary sands in Dakar, Senegal. On-site sanitation was mapped using object-oriented classification and visual interpretation of high-resolution, optical satellite images and ground-truthing surveys. Groundwater quality was assessed over a three-year period (2017–2019) from a network of 61 sources comprising boreholes, dug-wells, hand tubewells and piezometers. More than 253,000 on-site sanitation facilities are identified over an area of 520 km2 with densities ranging from 1 to 70 per hectare. A moderate, statistically significant linear relationship (r2 = 0....
Two billion people still consume drinking water contaminated with faeces. To improve this situati... more Two billion people still consume drinking water contaminated with faeces. To improve this situation, it has been recognised by UNICEF and the WHO that a more rapid approach to detecting faecally contaminated drinking water is necessary. We have previously demonstrated that fluorescence spectroscopy is a significant real-time indicator of the presence/absence and number of faecal indicator bacteria in drinking waters in low-income countries of the tropics. We have also established its potential as an online indicator of faecal contamination of public water supplies in the UK. Outstanding questions remain, however, over the source of the fluorescence and its uniqueness to faecal-indicator bacteria. To address these, we sampled potable groundwater supplies in Kenya, Malawi, Senegal and Uganda across an urbanisation transect from rural Malawi through to the city of Dakar (Senegal) where pollution sources and pressures vary considerably. We report on whether the fluorescence signal in th...
Fluorescent natural organic matter at tryptophan-like (TLF) and humic-like fluorescence (HLF) pea... more Fluorescent natural organic matter at tryptophan-like (TLF) and humic-like fluorescence (HLF) peaks is associated with the presence and enumeration of faecal indicator bacteria in groundwater. We hypothesise, however, that it is predominantly extracellular material that fluoresces at these wavelengths, not bacterial cells. We quantified total (unfiltered) and extracellular (filtered at < 0.22 µm) TLF and HLF in 140 groundwater sources across a range of urban population densities in Kenya, Malawi, Senegal, and Uganda. Where changes in fluorescence occurred following filtration they were correlated with potential controlling variables. A significant reduction in TLF following filtration (ΔTLF) was observed across the entire dataset, although the majority of the signal remained and thus considered extracellular (median 96.9%). ΔTLF was only significant in more urbanised study areas where TLF was greatest. Beneath Dakar, Senegal, ΔTLF was significantly correlated to total bacterial c...
All in-text references underlined in blue are linked to publications on ResearchGate, letting you... more All in-text references underlined in blue are linked to publications on ResearchGate, letting you access and read them immediately.
Schriftenreihe des Vereins fur Wasser-, Boden- und Lufthygiene, 2000
Dakar is a peninsula inhabited by a population of about 2 million people in 1996. In some dug wel... more Dakar is a peninsula inhabited by a population of about 2 million people in 1996. In some dug wells and piezometers, the nitrate content (NO3.) in the groundwater is above the World Health Organization (WHO) limit of 50 mg/l. In the unconfined part of the aquifer of the peninsula, all the samples from wells are contaminated by high nitrate contents which increased over time from 100 mg/l in 1987 to more than 250 mg/l in 1996. Only a limited area is affected by nitrate pollution in the confined layer. The results indicate anthropogenic pollution, a fact which indicates the increasing risk of pollution of drinking-water resources. Studies in the unsaturated zone and familiarity with the sanitation practices in the area indicate that the horizontal and vertical flux are linked mainly to defective septic tanks and direct organic waste elimination into the soil by more than 40% of the inhabitants. The correlation between tritium values (3H) and nitrate shows that the source of nitrate is...
Meeting: International Conference on Advances in Ground Water Hydrology, 16-19 Nov. 1988, Tampa, ... more Meeting: International Conference on Advances in Ground Water Hydrology, 16-19 Nov. 1988, Tampa, Fla., US
This study intends to see the temporal and spatial evolution of groundwater salinization at the n... more This study intends to see the temporal and spatial evolution of groundwater salinization at the northern and western zone of the CT aquifer in the Sine-Gambie region (Senegal). To do this, a hydrochemical study was conducted in 2015 and compared with previous studies (2000 and 2012). This study is essentially based on the two parameters, electrical conductivity and chloride content. The results obtained show that the evolution of salinity observed in these areas is explained by a contamination of the groundwater by the waters from the Saloum River and the sea. The comparison of groundwater electrical conductivity maps showed a salinity increase between 2000 and 2015; with a salinization phenomenon which increases toward inland in phase with chloride levels that doubled in some wells. The study also shows that several calcium bicarbonate facies have evolved to calcium chloride facies, and calcium chloride facies to chloride sodium facies.
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