Water quality assessment of agro wells in Vavuniya district for the use of agricultural and domestic purposes

Abstract

This study was conducted to assess agro-well water quality for the use of agriculture and domestic purposes in Vavuniys District. Water quality assessments were done on randomly selected 10 wells in the Thandikulum and Kurumakadu area from July, 2004 to October, 2005. pH, turbidity, conductivity, and feacal coliform were analyzed using the water quality kit while Nitrate-N, Nitrite-N, Ammonia-N, Phosphate, Chloride, Fluoride, Calcium, Magnesium, Sulphate, were analyzed using the UV/Visible Spectrophotometer. Nitrate-N was analyzed using the Ultraviolet Spectrophotometric screening method and others were analyzed with colorimetric methods. Even though, the agro wells are constructed for agricultural purposes, due to the water scarce conditions more than 70% of the wells are used for drinking, washing and bathing purposes too. In all wells, Turbidity, Nitrite-N, Sulphate, Chloride, Electrical conductivity were within the recommended level for drinking water. The feacal coliform (thermotolerant E.coli) was much higher in wells near residential areas. Nitrate-N was above the recommended level of 10 mg/l for drinking water in some wells. For agricultural purposes, the recommended range 5-30 mg/l of Nitrate-N was not exceeded by any of the wells. The ammonia concentration was increased after rainfall and it exceeds the recommended level of 0.2 mg/l. The maximum limit of Fluoride for insignificant risk (1.5 mg/l) was exceeded by some of the wells and were in the range of 0.28 mg/l to 1.74 mg/l.Based on the recharge estimates, depths of well, nearness to agricultural,livestock and pit latrine, the areas associated with the agro wells were categorized into three aquifer vulnerability zones; AVA1, AVA2 and AVA3. Deeper wells away from the pollution sources are better for domestic purposes compared to the others. This research indicates that the water quality of agro wells is recommended for agricultural purposes in this area but not for drinking purposes unless these wells are located in AVA3 zone and the water is treated.