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Influence of surface water infiltration on groundwater Fluoride concentration in an area of endemic Fluorosis in Sri Lanka

IWRA World Water Congress 2008 Montpellier France
1. Water availability, use and management
Ashvin Kamal Wickramasooriya * and Hingulwala Arachchilage Dharmagunawardena ** * Faculty of Applied Sciences, South Eastern University of Sri Lanka, Sammanthurai (E.P), Sri Lanka, telephone : 0094-67-2260073, e_mail : awickramasooriya@yahoo.com **

Keyword(s): fluoride, infiltration

AbstractFluoride is an essential element for the human body because it promotes dental health, essential for growth of bones and also permits tooth decay. Many health problems may arise by either deficiency or excess of Fluoride. Drinking water is the main source of Fluoride required by humans. Therefore, Fluoride concentration in drinking water may influence on human health caused by Fluoride. Majority of the Sri Lankan population does not have modern pipe-bone water systems especially in the rural areas. They depend on surface water and groundwater sources such as dug and deep hand pump wells, rivers and channels for their domestic water requirements. Therefore, study of the natural hydraulic processes and their effect on the behavior of Fluoride in surface water and groundwater are great importance in these areas. A problem of growing concern is the excessive concentrations of Fluoride found in many low plains of the dry zone, notably in the Anuradhapura and Polonnaruwa districts. The Fluoride concentration in many wells of these areas exceeds 1.5 mg/l and poses a health hazard to the consumers.in In these areas, wide prevalence of dental fluorosis specially among children of school going age. The slow rate of groundwater movement and high evapo-transpiration in the low plains of the dry zone tend to increase the Fluoride concentration.Within the areas of high Fluoride bearing groundwater, it is still possible to find certain areas specially close to an irrigation tanks, with considerably low Fluoride concentrations with regards to the safe limits of drinking water standards. Since surface water contain low Fluoride concentrations compared to groundwater by infiltration of surface water from the irrigation tanks could be a major governing factor for this situation. The possible effects of hydraulic processes specially the surface water infiltration of Fluoride content of groundwater was studied in the Polonnaruwa district, in a small village situated below the major irrigation tank; Parakrama Samudraya. The behavioral patterns of the groundwater table and groundwater Fluoride content revealed that the concentration of Fluoride in groundwater of the area is controlled by the infiltration of the surface water from the tank and the irrigation channel. It was found that the Fluoride of groundwater is low in the vicinity to the surface water bodies especially in the down-slope sides. Fluoride concentration increases in the direction of groundwater flow and away from the surface water bodies within the area of influence of the surface water. On account of the widely spread surface water irrigation network in the Polonnaruwa district, it could be expected that the low Fluoride areas close to irrigation tanks and channels are a result of infiltration and dilution of Fluoride content by the surface water.
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