Assessment of Groundwater Nitrate Level and Source of Pollution within Dire Dawa City, Dire Dawa, Eastern Ethiopia

Abstract

This research was conducted to study the ground water nitrate level, bacterial contamination and its sources. To achieve the objective, water samples were collected from 32 water points in both rural and urban areas for testing nitrate, chloride, sulfate and fecal coliform using photometer and membrane filtration method. The research revealed that nearly 86 percent of the study area was polluted with nitrate which exceed the natural/normal 9 mg l -1 nitrate in the groundwater. The pollution was very high in the urban center and advances from the southeastern part towards the north and northwestern part of the study area. The maximum concentration of nitrate (89 mg l-1 ) was found in Addis Ketema and Ras Hotel area while minimum concentration (0.86 mg l-1 ) at Tome area which is far away from the town. Moreover, the result showed that the concentration of nitrate unevenly declines with increasing water well depth. The research also finds out that the source of nitrate was mainly attributed to infiltration of sewage from the pit latrines. Moreover, fecal coliform was found in 36 percent of the water wells covering nearly 56 percent of the study areas. The presence of fecal coliform clearly indicates the source of pollution is feces. The main determinant factor for the presence or absence of bacterial contamination is the confined aquifer nature of the water well. The correlation plot of nitrate versus chloride and sulfate indicated that there was low or no correlation in the urban center while average correlation away from the town area mainly related to the presence of excreta (single factor) that contribute for the rise of chloride. In general, the nitrate and bacterial pollution covers 86 percent and 56 percent of the study areas with the pollution source is mainly traced back to infiltration of sewage from the pit latrines