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On-site sanitation density and groundwater quality : evidence from remote sensing and in situ observations in the Thiaroye aquifer, Senegal

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 ¼ 0.55, p « 0.01) is found between the density of on-site sanitation facilities and nitrate concentrations in sampled groundwater sources. Groundwater contamination beyond the WHO drinking-water guideline value (50 mg/L) occurs where densities of on-site sanitation facilities exceed 4 ( ±4) per hectare, a threshold commonly surpassed in peri-urban areas underlain by the Thiaroye aquifer of Dakar.

Auteur(s) : Mor Talla Diaw, Seynabou Cissé- Faye, Cheikh Bécaye Gaye, Seydou Niang, Abdoulaye Pouye, Luiza C. Campos and Ricahard G. Taylorr
Pages : 13 Pages
Année de publication : 2020
Revue : Journal of water, Sanitation and Hygiene for development
N° de volume : Published online: in press 2020
Type : Article
Statut Editorial : IWA Publishing 2020
Mise en ligne par : CISSE Seynabou