Abstract—The chemical and physical parameters of groundwater in some areas of dry and wet zones of Sri Lanka are described. Hydrochemical data from 114 water samples are used to evaluate water quality and to identify the processes that control fluoride levels in water. The results indicate that fluoride levels of groundwater in the dry zone are very high (< 8.0 mg/L) compared to those of the wet zone (< 0.8 mg/L). The measured nutrients (NO3- < 15 mg/L, PO43− < 5 mg/L) concentrations and chemical oxygen demand (< 18 mg/L) in both regions inferred that higher fluoride levels reported in the groundwater are not from anthropogenic sources. The pH-Eh stability diagrams show that nitrate, phosphate and iron does not co-exist with fluoride under prevailing redox condition. Physical parameters further show that fluoride values increase in slightly alkaline in pH (7.5-8.2), relatively low EC (1.0-2.5 mS/m) and highly oxidized water (50-200 mV). Groundwater movements of shallow regolith aquifers in the country are mainly controlled on joint and fault system in the partially weathered basement. This study observed that their variation in the dry and wet zones is a major parameter for the control fluoride levels in water. Thus less fractured rocks in the dry zone water discharge areas show higher values and may be due to lesser mixing of water with non-fluoride sources. Conversely, highly fractured rocks are predominant in the wet zone and hence mixing of fluoride poor and rich waters in both recharge and discharge regions in the zone results in low fluoride levels.

Index Terms—groundwater, fluoride, physical properties.

^aShimane University, Graduate School of Science and Engineering, Department of Geosciences, 690-8504, Matsue, Japan.
^bPeradeniya University, Department of Geology, 20400, Peradeniya, SriLanka.
¹Corresponding author. Shimane University, Graduate School of Scienceand Engineering, Department of Geosciences, 1060 Nishikawatsu-cho, Matsue, 690-8504, Japan. Tel: +81 08056208290; Fax: +81 0852326469
Email: taranga23@yahoo.com
² Tel: +81 852326459 Email: Ishiga@riko.shimane-u.ac.jp
³ Tel: +94 812389156, apitawala@pdn.ac.lk

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Cite: D. T. Jayawardana, H. M. T. G. A. Pitawala and H. Ishiga, "Groundwater Quality in Different Climatic Zones of Sri Lanka: Focus on the Occurrence of Fluoride," International Journal of Environmental Science and Development vol. 1, no. 3, pp. 244-250, 2010.