Assessment and mapping of groundwater quality for drinking purposes: A case study on Vallipuram coastal area, Jaffna peninsula, Sri Lanka.

Abstract

The people of the Jaffna Peninsula completely rely on groundwater for all of their water requirements. The Vallipuram water supply scheme has been started by National Water Supply & Drainage Board (NWS&DB) with the construction of four groundwater wells in the Vadamarachchi sand dune aquifer. However, due to the over-extraction of groundwater from these wells, there could be a severe groundwater imbalance in the area, where aquifers are depleting and the water table is lowering. Therefore, the present study was designed to identify the availability and quality of the well water surrounding a 1.5 km radius from the four NWS&DB dug wells, and 120 domestic wells were selected for the study. This study aims at the assessment and mapping of groundwater quality parameters and assessing the Water Quality Index (WQI) to determine the potability of groundwater. Sample collection and water quality analyses were conducted according to using standard procedures. The coordinates of each sampling location were established using Global Navigation Satellite System (GNSS) RTK Receivers at the site and an interpolation technique was used to analyze the spatial patterns of drinking water quality parameters in the case study area. The Weighted Arithmetic Water Quality Index method was used to find the suitability of water for drinking purposes. The test results revealed that turbidity, colour, TDS, total hardness, total alkalinity, Chloride, Fluoride, Total Iron, Calcium, and Sulphate concentrations exceeded the Sri Lankan drinking water quality standards values. Further, pH, nitrate, nitrite, and total phosphates are within the Sri Lankan Standards for all 120 wells. Heavy metals such as Arsenic and cadmium were not detected in any of the samples but lead contamination was detected in six samples. The microbiological results indicate that the entire study area was contaminated with total coliform and E.coli bacteria. According to the physical and chemical parameters, the WQI value varies from 4.5 to 287.2 and 72 wells are suitable for drinking purposes. When microbiological parameters were incorporated, a mere 3 wells were deemed suitable for drinking purposes. Therefore, it is highly recommended to conduct regular chlorination or disinfection of the wells.