An assessment on the effectiveness of the sanitary seal in protecting boreholes from contamination: A case of Mbare Suburb, Harare. (June 2022) - Takavada, Iginations
Abstract: Zimbabwe is projected to suffer water stress by 2025. Water availability is decreasing in the capital Harare, particularly in high density settlements where people rely mainly on boreholes. Anthropogenic pollution and poorly constructed boreholes lead to high levels of bacteriological contamination of borehole water sources, posing an increased risk of diarrheal disease for beneficiaries. To mitigate the risk of recurrent diarrheal outbreaks, Médecins Sans Frontiers piloted the incorporation of borehole sanitary seal in accordance with the local geology while drilling new boreholes in Harare. This study compared physical, chemical and bacteriological parameters between boreholes with two different sanitary seal types and no sanitary seal in Harare's Mbare suburb. 14 boreholes were classified into three categories based on the installed sanitary seal. Water quality analysis were conducted to describe physical, chemical and bacteriological parameters across three categories. The three categories included 4 boreholes with no seal, 6 with 3–6 m seal (random seal) and 4 with 18–25 m seal (proper seal; done in accordance with local geology). Water samples were collected between February 2019 to January 2020 in 3 sampling periods and analysed according to APHA standards. Groundwater vulnerability assessment to map pollution risk of the study areas showed 80% of the study area had high vulnerability. Results of water quality analysis revealed that only boreholes with 18–25m sanitary seal satisfied the WHO guidelines for drinking water. This study suggests that local geology should be considered to install borehole sanitary seals for contaminated shallow water aquifers in urban settlements. Highlights: Groundwater extraction is increasing in Harare as surface water continuously decrease in quality due to pollution and failure by the City council to treat the water to good quality. Mbare is highly vulnerable to pollution as 80% of the area had high vulnerability Index. Water quality for boreholes drilled in highly vulnerable area and equipped with proper sanitary seal in satisfied the WHO guidelines for drinking water. Therefore, sanitary seals are effective in protecting boreholes from contamination if constructed according to the local geology. The local geology should be considered when installing borehole sanitary seals in contaminated shallow water aquifers.