Study of Heavy and Trace Elements in Regional Groundwater Around MahaOya Thermal Springs

Abstract

Clusters of thermal springs are observed at ten localities along the Highland and Vijayanlitho- techtonic boundary of Sri Lanka (Dissanayake and Jayasena, 1988). MahaOya is one such cluster of thermal springs.The thermal springs are situated about 3 km north of MahaOya town on A5 road. The selected study area falls near the boundary between the Eastern province and Uva province and bounded by 7° 18’ and 7° 35’N and 81° 14’ and 81° 25’E. The area is characterized by rolling topograghy dominated by some flat terrains around 50m above mean sea level. The area is underlain by the Vijayan Complex (Chandrajith et al., 2013; Dissanayake and Jayasena, 1988). Granitic gneisses, granites and dolerite are the common rock types found (Cooray, 1994, 1984).

In terms of climate, MahaOya is located in the dry zone of Sri Lanka The average temperature of the area is in between 33.3ºC and 34.7ºC. The highest temperature is recorded in the month of August. The average annual rainfall is about 1500mm gaining from the Northeastern monsoon during the period of October to February. The area falls within the drainage basin of MahaOya, which flows, from Southwest to Northeastern direction. MahaOya thermal spring clusters are situated within a distance of 1-1/2 km from the river. MahaOya thermal springs consist with seven thermal springs having mean flow rate of 3 L per minute. Springs never run dry in dry period. The thermal springs show a surface temperature range of 37 - 55 C.

Thermal water sometimes mix with regional or local groundwater and surface water. Such mixing can be identified with their geochemical characterization (Gibson and Hinman, 2013; Petrini et al., 2013; Vitale et al., 2008). Thus, the study intended to analyze the regional and intermediate groundwater around the springs and thermal water in order to examine any relationship between different water categories. The database can be developed into a model which could predict possible occurrences of thermal springs.

Methodology

Eighty four locations including dug wells, tube wells and thermal springs were sampled in the study area. Those included seven thermal springs, seventy three dug wells and four tube wells. It is important to note that one dug well (L8) is located very close to the thermal springs and all other wells were selected within the extent of 2 km from the MahaOya thermal springs. The electrical conductivity was measured in situ with Orion 3 Star EC meter. The collected water samples were analyzed for 21 parameters including major cations, anions, heavy metals and trace elements. Cations, heavy metals and trace elements concentration with the Varian standard solutions were used for the calibration of the instrument. Anions including SO4 ,Cl and HCO3 were measured using standard methods. (APHA, 2005). The major cations and anions were plotted in the Piper plot in order to distinguish the water types with their chemistry. Visual MINTEQ software was used to identify the possible speciation, saturation indices and geochemical composition of water. Principal Component Analysis was performed by using Minitab software in order to generate a correlation between different water types in terms of their chemical composition.