Hydrogeochemical distribution and characteristics o f groundwater in Weligama area - in Southern Sri Lanka

Abstract

Groundwater table behavior and physico-chemical properties of the aquifer system in Weligama bay area were studied selecting 43 dug wells distributed over an approximately IS km2 area. Weligama is located in 80°22’Lat and, 5° 97 long; main river basin of the area is PolWattumodara Ganga. Continuous monitoring conducted from May to November 200S pertaining to groundwater levels, Electrical conductivity, total dissolved solids and salinity helped to prepare hydrogeological map and hydrogeochemical map of the area using the GIS package MAPINFO. Most of the dug wells distributed in the area are shallow and 3-5 m in depth and 0.5- 1.5 m diameter. According to the results of the chemical analysis in groundwater, distribution maps of Na+, K+, Mg2'*' and Ca2+ ions in the unconfined aquifer was plotted. The maps indicate distribution of the major ions in the groundwater associate with aquifer characteristics. The Mg2+: Ca2+ ratio of the groundwater various in between 0.5- 0.7 in the coastal line where the calcareous sandstone is dominant. Th£ Mg2+: Ca2+ ratio between 0.7- 0.9 in the western region where groundwater is distribute in the hard rock. The rest of the area Mg2+: Ca2+ ration is more than 0.9 where groundwater available in the alluvium aquifer.