4 research outputs found
The public health significance of latrines discharging to groundwater used for drinking.
Faecal contamination of groundwater from pit latrines is widely perceived as a major threat to the safety of drinking water for several billion people in rural and peri-urban areas worldwide. On the floodplains of the Ganges-Brahmaputra-Meghna delta in Bangladesh, we constructed latrines and monitored piezometer nests monthly for two years. We detected faecal coliforms (FC) in 3.3-23.3% of samples at four sites. We differentiate a near-field, characterised by high concentrations and frequent, persistent and contiguous contamination in all directions, and a far-field characterised by rare, impersistent, discontinuous low-level detections in variable directions. Far-field FC concentrations at four sites exceeded 0 and 10 cfu/100 ml in 2.4-9.6% and 0.2-2.3% of sampling events respectively. The lesser contamination of in-situ groundwater compared to water at the point-of-collection from domestic wells, which itself is less contaminated than at the point-of-consumption, demonstrates the importance of recontamination in the well-pump system. We present a conceptual model comprising four sub-pathways: the latrine-aquifer interface (near-field); groundwater flowing from latrine to well (far-field); the well-pump system; and post-collection handling and storage. Applying a hypothetical dose-response model suggests that 1-2% of the diarrhoeal disease burden from drinking water is derived from the aquifer, 29% from the well-pump system, and 70% from post-collection handling. The important implications are (i) that leakage from pit latrines is a minor contributor to faecal contamination of drinking water in alluvial-deltaic terrains; (ii) fears of increased groundwater pollution should not constrain expanding latrine coverage, and (iii) that more attention should be given to reducing contamination around the well-head
Safe distances between groundwater-based water wells and pit latrines at different hydrogeological conditions in the Ganges Atrai floodplains of Bangladesh.
BACKGROUND: Groundwater drawn from shallow tubewells in Bangladesh is often polluted by nearby pit latrines, which are commonly used toilets in rural and sub-urban areas of the country. METHODS: To determine the minimum safe distance of a tubewell from a pit latrine in different hydrogeological conditions of Bangladesh, 20 monitoring wells were installed at three study sites (Manda, Mohanpur and Bagmara) with the vertical and horizontal distances ranging from 18-47 to 2-15 m, respectively. Water samples were collected three times in three seasons and tested for faecal coliforms (FC) and faecal streptococci (FS) as indicators of contamination. Soil samples were analysed for texture, bulk density and hydraulic conductivity following standard procedures. Sediment samples were collected to prepare lithological logs. RESULTS: When the shallow aquifers at one of the three sites (Mohanpur) were overlained by 18-23-m-thick aquitards, the groundwater of the monitoring wells was found contaminated with a lateral and vertical distances of 2 and 31 m, respectively. However, where the aquitard was only 9 m thick, contamination was found up to lateral and vertical distances of 4.5 and 40.5 m, respectively. The soil textures of all the sites were mainly composed of loam and sandy loam. The hydraulic conductivities in the first aquifer at Manda, Mohanpur and Bagmara were 5.2-7.3, 8.2 and 1.4-15.7 m/h, respectively. CONCLUSIONS: The results showed that the safe distance from the tubewell to the pit latrine varied from site to site depending on the horizontal and vertical distances of the tubewell as well as hydrogeological conditions of a particular area
Safe distances between groundwater-based water wells and pit latrines at different hydrogeological conditions in the Ganges Atrai floodplains of Bangladesh
Background: Groundwater drawn from shallow tubewells in Bangladesh is
often polluted by nearby pit latrines, which are commonly used toilets
in rural and sub-urban areas of the country. Methods: To determine the
minimum safe distance of a tubewell from a pit latrine in different
hydrogeological conditions of Bangladesh, 20 monitoring wells were
installed at three study sites (Manda, Mohanpur and Bagmara) with the
vertical and horizontal distances ranging from 18\u201347 to
2\u201315 m, respectively. Water samples were collected three times in
three seasons and tested for faecal coliforms (FC) and faecal
streptococci (FS) as indicators of contamination. Soil samples were
analysed for texture, bulk density and hydraulic conductivity following
standard procedures. Sediment samples were collected to prepare
lithological logs. Results: When the shallow aquifers at one of the
three sites (Mohanpur) were overlained by 18\u201323-m-thick
aquitards, the groundwater of the monitoring wells was found
contaminated with a lateral and vertical distances of 2 and 31 m,
respectively. However, where the aquitard was only 9 m thick,
contamination was found up to lateral and vertical distances of 4.5 and
40.5 m, respectively. The soil textures of all the sites were mainly
composed of loam and sandy loam. The hydraulic conductivities in the
first aquifer at Manda, Mohanpur and Bagmara were 5.2\u20137.3, 8.2
and 1.4\u201315.7 m/h, respectively. Conclusions: The results showed
that the safe distance from the tubewell to the pit latrine varied from
site to site depending on the horizontal and vertical distances of the
tubewell as well as hydrogeological conditions of a particular area