Analysis of Groundwater Quality and Identification of Abstraction Points in Kahawa Wendani, Kiambu County

Abstract

Surface water is not enough to meet the needs of the increasing populace, which has led to groundwater use as an alternative source globally. It therefore becomes essential to monitor groundwater levels and quality to enhance water resource management and protection (Foster, 2002).The main objective of this study was to assess the groundwater quality and position the abstraction points on the map of the study area. Ground Water samples were collected from ten selected boreholes in Kahawa Wendani and each sample coded uniquely and systematically such as B1 for borehole one. The sampling period fell in the month of October, 2016 which was a hot and dry season. Sampling was by snowballing due to the unknown population size. Boreholes were identified and their geographical position shown on a map using ArcGIS software version 10.2.2.Two different samples (chemical/biological) were taken from each borehole. Samples for chemical analysis were collected in one litre plastic bottles prepared according to the WHO standard laboratory method. While those for biological analysis were collected in standard glass bottles well corked and with Aluminium foil reinforcement. The depth of the boreholes was also recorded. 19 parameters were selected for analysis, tested in accordance with the WHO Standard methods for the Examination of water and waste waters and their results compared to WHO drinking water standards. All the parameters measured in all the samples were within the required standards except fluoride and iron. Iron (Fe2+) ranged from 0.1mg/l in three samples,1, 2 & 3 and 0.3mg/l in boreholes 5, 6 & 8 compared to the WHO standard value of 0.3 mg/l. Fluorides recorded the highest value of 1.92mg/l in borehole 1 compared to the WHO standard value of 1.5mg/l. Groundwater in Kahawa Wendani is suitable for drinking purposes. However, the levels of fluoride in boreholes 1 (1.92mg/l), 4 (1.54mg/l) & 5 (1.84mg/l), which were above 1.5mg/l, the WHO standard value, should be managed by the relevant authorities before they exceed this threshold to avoid risk to health. This implies that the aquifer in this site has fluoride deposits as the area falls in the hydrogeological zone made of volcanic rocks. The groundwater abstraction points were found to be clustered in distribution towards Matopeni and Booster areas of the study. Meaning more groundwater is abstracted in these particular positions in Kahawa Wendani. Further research should be done to achieve the trend in groundwater quality not only for this site but across the nation in order to have a reliable groundwater database.