Assessment Of Dissolved Ions And Microbial Coliforms In Water From Selected Sites Of The Upper Athi River Subcatchment Area, Kenya.
Muraga, Joseph Mwangi
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The Upper Athi River sub-catchment area has experienced exponential growth of human population since the turn of the century. This has led to establishment of satellite towns such as Ngong, Kiserian, Ongata Rongai, Mlolongo, Kitengela and Ruai. These towns have either no or inadequate supply of water from the local governments, that is, Kajiado, Machakos and Nairobi. Communities in this area of study have therefore resorted to obtaining ground water through drilling boreholes and digging shallow wells for their domestic needs. This is done without proper information on whether the water meets quality standards set out by Kenya Bureau of Standards (KEBS). This study therefore sought to assess the water quality in this area to determine whether ground water meets these standards. It also compared these levels of dissolved ions and coliforms to those of river water in the recharge area of the Upper Athi sub-catchment area. Twenty one water samples comprising of eleven boreholes, five shallow wells and five river water samples were collected from the Upper Athi sub-catchment area in the months of December 2011 which was a dry month and in May 2012 which was a wet month. The samples were analysed for dissolved ions and microbial coliforms. The metal ions analysed included Ca, Cd, Cr, Cu, Fe, Mg, Mn, Na, Pb and Zn while anions included Cl-, CO32-/HCO3-, F-, NO2-/NO3- and SO42- as well as faecal coliforms. Physical parameters analysed included pH, electrical conductivity (EC) turbidity, total dissolved solids and colour. The analysis of cations was carried out using atomic absorption spectrophotometry while chlorides and total alkalinity were analysed using titrimetric method. Levels of fluoride and nitrate were analysed using ion selective electrodes, sulphate using gravimetric method and microbial coliforms using lactose broth methods. The results showed that levels of dissolved ions in ground water were higher than in surface water while surface water had higher number of faecal coliforms. The high levels of dissolved ions in ground water was attributed to the geology of area while high levels of iron and faecal coliforms in river water samples was attributed to anthropogenic activities The results from the samples analyzed show that pH of boreholes and shallow wells (ground water) water was higher than that of river water (surface water). pH levels ranged from 7.16±0.003 - 9.34±0.004 for ground water and 7.24±0.002-8.00±0.003 for surface water. Electrical conductivity was also higher in ground water ranging from 669±0.002μS/cm-1568±0.004μS/cm while that of surface water ranged from 382±0.003μS/cm-1202±0.002μS/cm at Magadi road. Turbidity was vi higher for surface water than that of ground water ranging from 74.3±0.004 NTU- 95.4±0.003 NTU and below detection limits (BDL) levels for ground water with the exception being borehole at Athi Primary school which had turbidity of 18.6±0.03 NTU. Colour was high for surface water ranging from 159±0.002 c.u to 343±.004 c.u while that of ground water ranged from 1.5±0.003 51.2±0.004 c.u in borehole 5 located at Athi Primary School. Total Dissolved Solids were higher in ground water ranging from 231.68.00±0.003mg/l - 1003.52±0.004mg/l in shallow well located at near Brookshine School, Kangundo road while that of surface water ranged from 244.48±0.002mg/l-769.28±0.003mg/l. From the chemical parameters analysis, fluorides were significantly higher in ground water ranging from 0.37±0.003 to 9.36±0.002 ppm at Mlolongo which exceeded the KEBS limits for drinking water of 1.5ppm. Iron levels were higher in river water samples ranging from 2.11±0.002 to 18.401±0.003 ppm at Kangundo Road Bridge. Even though ground water had lower levels of iron that river water, it ranged from <0.001ppm to 1.93ppm against the 0.3ppm recommended by KEBS. Lead levels in ground water ranged from <0.001ppm to 2.64ppm at borehole BH4 located at Brookshine School. This was way above the recommended levels of 0.03ppm by KEBS. The levels of microbial coliforms were higher in river water ranging from 140-294 c.f.u/100ml during the dry month of December 2011 and 156-309 c.f.u/100ml during the wet month of May 2012. Ground water recorded coliforms ranging from zero to 40 c.f.u/100ml. Within the ground water system shallow wells had a higher count of coliforms than in boreholes. The high levels of fluorides have led to increased cases of dental fluorosis especially among young children in the area of study. Adults are at risk on increased bone fractures in their lifetime. High levels of lead in some ground water could lead to mental retardation since lead is a very toxic metal even at very low levels. There is therefore need to develop a long-term plan of providing safe drinking water by the county governments. There is also the need to establish regulations that require private water vendors and water companies to invest in water treatment plants that reduce levels of dissolved ions in ground water before distributing the water to local communities
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