Monsoon effect on the variation of groundwater quality in Vavuniya City area, Sri Lanka

Abstract

Groundwater is one of most precious natural resources and the assessment of groundwater quality is the key towards protecting and conserving the quality of groundwater. The objective of this study is to assess the groundwater quality of Vavuniya city during pre and post- monsoon phases and identify the monsoon effect on groundwater quality variation. Samples were collected from Nine (09) common drinking water wells within the radius of 5 km from the centre of the Vavuniya town during the year 2016 (Pre-monsoon: July, August and September) and 2017 (post-monsoon: January, February and March). Electrical conductivity (EC), Turbidity, total dissolved solids (TDS) and pH were tested at the site using portable HACH branded instruments. Total hardness (TH), Calcium and chloride ions were measured by titrimetric method and nitrate, phosphate, fluoride and sulphate ions were measured by reference method of HACH DR5000 at regional laboratory Vavuniya. All the testing procedures were based on APHA (2005) and SLS 614:2013. Turbidity, EC, TDS, TH, and Calcium, nitrate, phosphate and chloride ions were high in post-monsoon period than pre monsoon period. pH and Alkalinity were almost the same in both periods and fluoride was high in pre-monsoon than post monsoon. High turbidity, high concentration of ions and high hardness in post-monsoon period may be due to dissociation and leachate of geochemical compounds into groundwater with rain, and contamination of well-water by runoff and seepage. High concentration of fluoride in groundwater may be due to high evaporation rate in pre-monsoon period. Mostly EC, TDS, TH, alkalinity and fluoride ion concentration were above the SLS 614:2013 level while turbidity, Calcium ions, nitrate and phosphate ions, and pH were within the SLS 614:2013 level in both periods.