Analysis of Raw Water Quality of Water Supply Intakes of Maha Oya

Abstract

Maha Oya is one of the main rivers in Sri Lanka, very much used for drinking waterextraction. It flows through five important districts of Sri Lanka offering water throughfourteen water supply intakes, eight of which are located along the main river while othersare scattered along the tributaries. Only three of the associated plants offer conventionaltreatment for water. This river receives much organic waste from the upstream. Industrialdischarges and harmful anthropogenic activities are common in the final stretch of the river.This study aims to investigate the contamination of Maha Oya water around each intakepoints along the main river and to find causes. Samples were collected from water supplyintakes during both high and low flow rate conditions. Analysis was done on pH, turbidity,DO, COD, BOD, phosphate, Nitrate, Sulfate, Chloride, Fluoride, Coliform and heavy metalswhich were selected based on the drinking water quality requirements of the country.According to the results, Mawanella Intake records high BOD and Coliform counts due to themunicipal and house hold discharges from the townships, overflow of Soakage pit and septictanks of Mawanella town during rainy seasons. Waste load coming from three tributariesconfluences was attributed to high values of BOD, COD and coliform count while cultivationin the vicinity has increased the nutrient at the Hirwadunna intake. COD value of thesampling location at the Allawwa intake is very high. As it is located in the Allawwa town,waste from the town is disposed to the river directly and concentration is very high duringlow flow conditions. Girulla intake is polluted mainly from bank erosion due to theanthropogenic activities like cay mining. COD and BOD values are comparatively high dueto direct discharges. Pollution associated with Bamukuliya intake is due to the discharge ofMakandura IP. The effect is reduced when it comes to the Bambukuliya intake even though itexceeds the COD for drinking water with simple treatment. Sea intrusion has not affected theBambukuliya intake due to the salinity barrier at Bambukuliya. Heavy metal concentration ofall intakes are below the respective standards.