Nitrate Pollution and Fecal Coliform Contamination in Domestic Wells in the Vavuniya District Sri Lanka with Special Reference to Hospital Area

Abstract

Ground water is generally  polluted by leachates  from sewage and  agricultural lands. The main pollutants from sewages are nitrate nitrogen and fecal coliform. Both are hazardous when its level at high concentration in drinking water.  The objectives of the study were to evaluate the nitrate nitrogen and fecal coliform count  in  wells and identify the wells that are not suitable for drinking purpose in Vavuniya District, Sri Lanka.  Thirty three   dug wells  and three tube wells were selected around the general hospital Vavuniya to measure the Nitrate Nitrogen (N0₃-N), and fecal coliform count from March 2008 to February  2009. Mean NO₃- N ranged from 0.40 to 16.2 mg/l over a twelve months period and  30.5 % of the wells were above the  permissible limit of 10mg/l (well No11,12,13, 17,18,20,21,23, 25, 29  & 33) and these  wells are not suitable for drinking purpose in almost all the months. Nitrate nitrogen in wet season was significantly higher than dry season (p= 0.072). The depth of wells varied from 4m to 8m and most of  these wells were shallow wells. Shallow wells  are very vulnerability to nitrate pollution  in permeable soil. Almost all the wells were contaminated  with fecal coliform.  Wells closer to sand beds  were contaminated with very high amount (more than 500) of  fecal coliform. Improper  sewage disposal system could be the reason for high nitrate nitrogen and  fecal coliform contamination in wells around the hospital area.