SHALLOW GROUNDWATER GEOCHEMISTRY IN A SELECTED AREA OF SAMANALAWEWA CATCHMENT

Abstract

The demand for freshwater is increasing due to the increasing population. As an alternative to the surface water, groundwater sources play a significant role in water-scarce areas. Groundwater quality is a major determinant of its suitability for human consumption purposes. The lower part of the Samanalawewa catchment area is known as water-scarce area with poor water quality during the dry season. Therefore, good quality groundwater may be an alternative water source for daily domestic consumption and the electrical resistivity survey helps to identify appropriate locations for groundwater. This research aimed to analyse the groundwater quality and potential areas with shallow groundwater around Sabaragamuwa University in the Samanalawewa catchment. Twenty groundwater samples from dug wells and eleven surface water samples from streams and pond were collected to analyse water quality. Alkalinity, hardness, pH, total dissolved solids, major anions and cations of the samples were analysed. Piper diagram was used to identify major groundwater types, and digital elevation models were used to identify the spatial distribution of water quality in the study area. Using the water levels respective to the mean sea level, a groundwater potential map was produced. Depending on groundwater quality results, fifteen vertical electrical soundings were carried out in the study area. In nineteen locations, pH levels of water exceeded SLS 614:2013 and WHO permissible levels and five locations exceed permissible levels for iron. According to piper diagram, Ca-HCO3 and Ca-Mg-Cl are the major groundwater types in the study area, and the abundance of cation and anion varied in the sequence of Ca2+ > Mg2+ > Na+ > K + and HCO3 - > Cl- > SO4 2- indicating rock weathering process being the leading cause for the composition of groundwater in the area. The results suggest, calcareous rocks may cause the groundwater types, however, the unpublished data suggest, the study area is lack of calcareous rocks. According to the developed groundwater potential map, the university premises is rather unfavourable for the shallow groundwater abstraction in terms of the groundwater flow pattern. The resistivity survey revealed the presence of eight locations with groundwater potential and two locations with better water quality