Conceptual model of the evolution of groundwater quality at the wet zone in Sri Lanka

The evolution of groundwater quality at a wet zone in Sri Lanka was made clear using field investigation, chemical and isotopic analyses methods. In the wet zone, the concentrations of major ions and electrical conductivity (EC) in the groundwater are low with small seasonal change. Except for sodium, silica and chloride, the EC and other major ion concentrations increase along the groundwater flow direction. The contributions of bicarbonate and calcium ions to the increase in EC are the largest among the major ions. The groundwater quality shows calcium-bicarbonate type, the initial stage of the Chebotarev series. There is a seasonal change in isotopic composition. The isotopically lighter groundwater was found at the valley bottom in the rainy season. Under the very heavy precipitation conditions, the slope of the regression line between [dgr ]D and [dgr ]18O and deuterium excess for groundwater are close to 8 and 10, respectively. In other cases, the slopes of the regression lines and deuterium excess are, less than 8 and 10, respectively.