The Effect of Septic Tanks Sewage Disposal System Distances on Borehole Water Quality in Ongata Rongai, Kajiado County, Kenya.
Onsite disposal of domestic effluent by septic tank systems is the most common method practiced by the people that live in Ongata Rongai in Kajiado County, Kenya. Moreover, water for domestic use is primarily supplied from private water boreholes because of absence of piped water and lack of sewerage system in the area. The main goal that this research was targeting was, to assess the effect of septic tanks disposal system on the borehole water quality. Water for physical, chemical and bacteriological laboratory analysis, was sampled from ten different boreholes at different distances from five septic tanks in the high to medium density settlement areas that rely on borehole water for their domestic use. The parameters analyzed and results were: pH 6.5±0.2 to 8.4±0.4; Turbidity 1.9±0.8 to 4.9±1.5 (NTU); Alkalinity 116±2.3 to 186.9±6.1 (mg/l); Phosphates below detection limit (BDL) to 0.12±0.01 (mg/l); Chlorides 134±3.8 to 144.4±4.6 (mg/l); Nitrite 4.12±1.1 to 16.8±1.0 (mg/l) ; Nitrate 2.17±1.5 to 7.07±3.2 (mg/l); Ammonia BDL to 1.4±0.7 (mg/l); Sodium 8±2.38 to 217±4.24 (mg/l); TDS 174±2.1 to 896±1.9 (mg/l); Conductivity 802±0.7 to 1265±1.32 (μS/cm), Sulphates 66.7±3.6 to 198±1.25 (mg/l); Phenol BDL to 0.15±0.0 (mg/l); COD 4.0 ±1.7 to 75.0 ±8.0 (mg/l); E.coli BDL to 3±1.0 (cfu), surfactants (as methylene blue active substances, MBAS) were not detected. The parameters analyzed are those that were relevant to the assessment of water contamination by domestic effluent disposal system. The differences in concentrations of the selected parameters were also determined in wet and dry seasons. The samples were collected in the months of March (dry) and May (wet), 2014, to represent the dry and wet seasons respectively. The levels of contaminants increased with decreasing distance from septic tank systems and were also higher in May, compared to March, 2014. Total dissolved solids (TDS), conductivity and sulphates did not show any seasonal variation in all the sites. The results indicated that the selected boreholes in Ongata Rongai that were more than 70 m away from the septic tanks, the values of most physico- chemical parameters were within the World Health Organization (WHO) standards. The findings from this study showed that water quality is affected by seasonal variations and the distance of the borehole from the septic tank sewage disposal system. The contamination problems in borehole water from Ongata Rongai call for stringent management measures to be put in place by the Kajiado County Government to safeguard the human health and environment.
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