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Safe Distances Between Groundwater-based Water Wells and Pit Latrines at Different Hydrogeological Conditions in the Ganges Atrai Floodplains of Bangladesh

M. Sirajul Islam
International Centre for Diarrhoeal Disease Research, Bangladesh, Mohakhali, Dhaka, 1212, Bangladesh

Zahid Hayat Mahmud
International Centre for Diarrhoeal Disease Research, Bangladesh, Mohakhali, Dhaka, 1212, Bangladesh

M. Shafiqul Islam
International Centre for Diarrhoeal Disease Research, Bangladesh, Mohakhali, Dhaka, 1212, Bangladesh

Ganesh Chandra Saha
Dhaka University of Engineering and Technology, Gazipur, Bangladesh

Anwar Zahid
Hydrogeology and Environmental Geology Section, Department of Geology, University of Dhaka, Dhaka, 1000, Bangladesh

AHM Zulfiquar Ali
Department of Soil, Water and Environment, University of Dhaka, Dhaka, 1000, Bangladesh

M. Qumrul Hassan
Hydrogeology and Environmental Geology Section, Department of Geology, University of Dhaka, Dhaka, 1000, Bangladesh

Khairul Islam
WaterAid Bangladesh, Banani, Dhaka, 1213, Bangladesh

Hasin Jahan
WaterAid Bangladesh, Banani, Dhaka, 1213, Bangladesh

Yakub Hossain
Village Education Resource Center, Savar, Dhaka, 1340, Bangladesh

M. Masud Hasan
Village Education Resource Center, Savar, Dhaka, 1340, Bangladesh

Sandy Cairncross
London School of Hygiene and Tropical Medicine, London, UK

Richard Carter
WaterAid, London, UK

Stephen P. Luby
International Centre for Diarrhoeal Disease Research, Bangladesh, Mohakhali, Dhaka, 1212, Bangladesh

Alejandro Cravioto
International Centre for Diarrhoeal Disease Research, Bangladesh, Mohakhali, Dhaka, 1212, Bangladesh

Hubert Ph. Endtz
International Centre for Diarrhoeal Disease Research, Bangladesh, Mohakhali, Dhaka, 1212, Bangladesh

Shah M. Faruque
International Centre for Diarrhoeal Disease Research, Bangladesh, Mohakhali, Dhaka, 1212, Bangladesh

John D. Clemens
International Centre for Diarrhoeal Disease Research, Bangladesh, Mohakhali, Dhaka, 1212, Bangladesh

Abstract/ Executive Summary:

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.

Keywords: Safe distances, Groundwater-based water wells, Pit latrines, Ganges Atrai floodplains, Bangladesh

Location: Three upazilas (sub-districts) namely Manda of Naogaon district and Mohanpur and Bagmara of Rajshahi district of Bangladesh

Start Date: 00-03-2008

End Date: 00-12-2008

Program Area: Risk Management in Agriculture

Commodity: Water pollution

Objectives:

The present study was carried out to determine a minimum safe distance between a tubewell and a pit latrine under different hydrogeological conditions in the Ganges Atrai flood plain areas of Bangladesh.

Methodology:

Study area

The study was conducted during the period from March to December 2008 in three upazilas (sub-districts) namely Manda of Naogaon district and Mohanpur and Bagmara of Rajshahi district of Bangladesh. The monsoon season (May to August) is included in the study period. Hydrogeologically, the study sites fall under the Ganges and Atrai flood plains bordered by the Barind Tract from the west, north and north-east. The soils of the study areas cover the agroecological regions of the Tista Meander Floodplain, Lower Atrai Basin and High Ganges River Floodplain. The tubewell water was free from arsenic and iron contamination. The depths of the latrines varied from 2 to 2.5 m. The water level in Manda, Mohanpur and Bagmara varied from 2–9.5, 4–14 and 1.5 to 10 m, respectively, during the study period.

Establishment of monitoring wells

The nest of monitoring wells in Manda upazila was installed at Master Para in Kusumba union. The area is located on the bank of the river Atrai and the river flows towards the southeast. Wells were installed at Manda, Mohanpur and Bagmara to monitor the groundwater flow from a target latrine at each site. Monitoring wells were installed along the groundwater flow path from the latrine. Each latrine was used by five persons or more for at least 1 year. The flow path was predicted by the examination of the local disposition of surface water, hand-tube wells and pumping irrigation wells.

Collection and analysis of samples

Soil samples were collected from three study upazilas by pit method until the water table was reached. Hydraulic conductivity rating of sediment was determined according to the method described by O’Neal. Bulk density was determined by core sampling method, and bulk samples were used for particle size analysis. A metallic core of known volume was pressed or driven into the soil at the desired depth and thus an undisturbed soil sample was collected. Mass of the soil sample was found by weighing after oven drying the soil. The volume was calculated from the core dimension used for drawing the sample. Particle size analysis was determined by the hydrometer method. Hydraulic conductivity was determined following the procedure described by Klute.

Sediment samples were collected during drilling of the wells and used to prepare the lithological logs in order to identify the sediment type and extension of the aquifers and aquitard. Manual hand percussion method was used by local drillers to drill the wells. Samples were collected from every 1.5-m depth. Representative samples were selected for sieve analysis of aquifer sediments to determine physical and hydraulic properties. The uniformity coefficient (Uc), i.e. D60/D10, of the sediment samples was calculated from grain-size analysis. The hydraulic conductivity of aquifer sediments was determined from the grain size distribution curve following Hazen’s method.

Water samples were collected from existing tubewells and from the established monitoring wells which were installed 1 week earlier following procedures described earlier. In brief, the tubewell mouths were first cleaned using tissue paper. The interior of the pump spout was sterilised using alcohol and a gas burner. The tubewell water was pumped out and allowed to flow for 2 min. Then, 500-ml water samples were aseptically collected in sterile Nalgene plastic bottles. All samples were transported directly to the Environmental Microbiology Laboratory of International Centre for Diarrhoeal Disease Research, Bangladesh (icddr,b) in an insulated box filled with cool packs (Johnny Plastic Ice, Pelton Shepherd, Stockton, CA, USA) and processed within 24 h. The monitoring wells were sampled three times to cover three seasons during the study period.

The FC and FS were counted following procedures described elsewhere [6, 28]. In brief, for FC and FS, 100-ml water samples were filtered through a 0.22-μm pore-size membrane filter (Millipore Corp., Bedford, MA, USA), and the filters were placed on membrane faecal coliforms (mFC) and KF-streptococcus agar plates. The mFC plates were incubated at 44 °C for 18 to 24 h. Then, the characteristic blue colonies were counted as FC and expressed as colony-forming unit (CFU) per 100 ml. The KF-streptococcus agar plates were incubated at 37 °C for 48 h, and the characteristic light and dark red colonies were counted as FS.

Source of Information: Journal of Health, Population and Nutrition volume 35, Article number: 26 (2016)

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Funding Source:

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Achievement/Findings:

Pit latrines enhanced microbial contamination of adjacent shallow tubewell water where hydrogeological conditions (i.e. thickness and hydraulic properties such as hydraulic conductivity of surface clay aquitard, depth of groundwater table and groundwater flow direction) played important role on the transport of bacteria. Existence and level of contamination of bacteria differed in different hydrogeological conditions in both lateral and vertical distances, and where the surface clay was thick and compact, there was less or no contamination. Where there was a contamination, the level also varied at different seasons. During monsoon, the contamination was higher due to higher infiltration rate of precipitation water and shallow depth to water table. The present study did not produce sufficient data to develop general guidelines for the entire Bangladesh for the minimum safe distance of a tubewell from a pit latrine. Therefore, further studies need to be conducted including more physiographic divisions of Bangladesh with different hydrogeological conditions. Though microbiological contamination of the groundwater was found, most wells sampled showed good bacteriological quality of water, mostly where the hydrogeological conditions did not allow the transport of bacteria.

Knowledge Management: Journal