Vulnerability and pollution of groundwater in Kisauni, Mombasa, Kenya

Abstract

Rapid urbanisation in the Mombasa District, and in paliicular the Kisauni area, has increased the demand for essential services, notably water supply and waste management infrastructure. This is manifested in inadequate clean drinking water from the reticulated supply, leaving the inhabitants with groundwater to supplement their resources, or in most cases as the sole option. An assessment of the intrinsic aquifer vulnerability to contamination was carried out by applying the DRASTIC model coupled with GIS analytical tools. Monitoring data on physico-chemical characteristics showed raised concentrations of nitrates in groundwater, in particular, in the more densely populated Kisauni areas, attributed to contamination from on-site sanitation systems dominated by pit latrines and septic tank-soak pit systems and uncollected municipal refuse. Concentrations ofN031/NOi 1-N ranged from 0.4 to 44.4mg 1-1, with an indication of seasonal variations. About 50% and 70% of the water samples tested in June/July and November, respectively, did not exceed the 10mg 1-1 N031/NOi 1-N guideline level set for potable water by WHO~ The Kisauni area is indicated as experiencing a high degree of groundwater contamination by microbial contaminants, especially in the high-density housing settlements, attributed to on-site· sanitation. The contamination levels are more severe during the rainy season, when aquifer recharge is high. A suggested strategy for intervention includes the control ofpollution sources, education and awareness creation, and the implementation of existing laws and regulations to protect and manage groundwater resources.