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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 up 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 times 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 from 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 bar 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 spatialtemporal
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
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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 provides recommendations to governmental and nongovernmental
institutions that are mandated with the responsibility of ground water
development planning and quality monitoring.