Abstract:
The study is primarily an assessment of groundwater quality in the Yatta Plateau of Kitui County. The study focused on the spatial temporal distribution of key chemical parameters namely pH, TDS, Colour, Total hardness, Turbidity, Conductivity, Total alkalinity, Fluoride and Iron. Yatta Plateau is a volcanic formation which is characteristically flat at the top thus limiting overland flow and depression storage necessary for other methods of water supply to the community resident on the Plateau. Surface water sources are therefore not readily available as most of the rain water percolates easily owing to the flat nature of the plateau. The development of groundwater sources has therefore taken preference to other sources of water supply in the study area. Reliable and good quality water supply on the Yatta Plateau corridor may be affected by the type of chemicals found in the ground water, concentration of the dissolved minerals or even ground water quality changes over time. The purpose of this study was therefore to determine the variability or changes on ground water quality in Yatta Plateau in relation to rainfall, land use, geology among others and determine how the same influences water utilization. Groundwater samples were collected in boreholes distributed on the plateau and the key physicochemical parameters were measured using standard methods . These were then analyzed in order to determine the variability of groundwater quality on the Yatta plateau, the extent of influences of the groundwater chemical parameters on water utilization and, finally come u p with recommendations on the appropriate ways of addressing groundwater quality degradation. The study is also important in that the findings provide a better understanding of possible changes in groundwater quality over time and this will prompt planning for appropriate treatment that is required to address the quality changes. The samples were collected in the period between March 2015 and March 2016 covering two dry seasons and two wet seasons experienced in the study area. Samples were collected four t imes from each of the six target boreholes. In total, twenty four (24) water samples were collected for analysis. The samples were analyzed at the Water Resources Management Authority (WARMA) Water Quality Testing Laboratory in Nairobi. The data obtained f rom the laboratory tests was analyzed using Surfer for spatial - temporal analysis, and were also subjected to Statistical analysis using SPSS (Statistical Package for Social Science). A questionnaire was also administered on the users of water derived from the sampled boreholes. The questionnaires were analyzed using various statistical methods including the analysis of variance (ANOVA), correlation analysis, and regression analysis, test of hypothesis, frequency distribution tables, means, percentages and b ar charts. The results of the study show that there is no direct relationship between rainfall and variations of groundwater quality in the Yatta plateau. It was however found that there was spatial - temporal variability in different groundwater quality parameters that were analysed. The spatial - temporal variability was attributed to differences in the geologic formations forming the aquifers of individual boreholes that were sampled within the study area. Although the groundwater is generally of good quality, electrical conductivity, TDS and fluoride were found to be increasing drastically and may surpass the WHO and KEBS drinking water standards in future. The increase in the parameters was attributed to the nature of the geological formations common on the plateau. The results of the analysis of the questionnaires showed that groundwater chemical parameters do not influence water utilization in the Yatta Plateau. The major water quality concern was taste and this was attributed to salinity. The study provide s recommendations to governmental and non - governmental institutions that are mandated with the responsibility of ground water development planning and quality monitoring.