Evaluation of groundwater quality and its suitability for drinking and irrigation use in east wollega zone of oromia regional state, nekemte, Ethiopia.

Abstract

The study was conducted to evaluate the groundwater quality in order to analyze the suitability of the water for drinking and Irrigation uses in the Nekemte Town of Oromia Regional State, Ethiopia. The study area lies between 9002’47”N to 9006’56” N latitudes and 36028’53”E to 36036’40”E longitude covering the six administrative zones of the town. Water samples were purposively collected from hand dug bore holes, hand dug wells, protected spring and pipe borne water and analyzed following standard methods for the examination of water quality (APHA, 2005). The study examined selected physical, chemical and biological qualities of water from hand dug bore holes, hand dug wells, protected spring and pipe borne. The water samples were analysised for Temperature, pH, turbidity, dissolved oxygen, conductivity, total dissolved solids, total alkalinity, bicarbonate, carbonate, total hardness and selected cations (Ca2+, Mg2+ , Na+ and K+ ) and anions (Cland SO4 2- ), heavy metals (Mn2+ and Fe2+) and Coliforms (Total coliforms and Faecal coliforms),Water Salinity, Sodium adsorption ratio (SAR), Residual sodium carbonate (RSC), Permeability index and Magnesium ratio between July 2015 and October 2015. Nonconservable water quality parameters such as Temperature, pH, turbidity, dissolved oxygen and conductivity were determined onsite immediately after sampling using handleld portable water quality measuring instrumentation. These parameters were used to analyze the suitability of groundwater for drinking and domestic purpose by comparing with the WHO and Ethiopian standards. The results show that most of the studied physical, chemical and bacteriological parameters of the groundwater samples were above acceptable limits set by the WHO for drinking and domestic purpose. The water quality observed at all sampling points except at S10 shows that temperature (range between 24.86-26.78 0C) and pH (range 4.76-6.67) were above and below acceptable limits of WHO guideline for drinking water respectively. In addition, the water quality observed at locations S2, S3, S4, S5, S6, S8 and S9 shows that higher levels of turbidity (ranges between 5.54 - 7.90 NTU) than WHO recommended of 5 NTU. Conductivity above WHO recommended limit was observed at location S2. High levels of manganese (ranging between 0.26 - 1.61mg/L) than WHO prescribed limit of 0.1 mg/l was observed at all locations except at S7. Data from locations S3, S5, S6, and S10 shows that the water contains higher concentrations of iron than the WHO standards of 0.30mg/L. The bacteriological analysis also revealed that, coliforms (Fecal and Total Coliform counts ranging between 11 - 530 and 264.11 - 7802.67 CFU/100 mL respectively) were detected in all the water samples including the pipe borne water. The detection of coliforms in the water samples is an indication of fecal contamination which has been contaminated implies that the Consumption of water from water sources may cause public health problems. Two triangles plot, one for cations and the other for anions were used to draw Piper-Hill diagram that is used to infer hydrogeochemical facies. The cations and anion fields were combined to show a single point in a diamond-shaped field, from which inference was drawn on the basis of hydro-geochemical facies concept. The results conclusively indicated that at the moment the groundwater and pipe borne water in the area is not safe for human consumption. Thus, some form of treatment is necessary to make the water suitable for drinking and domestic use. However, to meet the millennium development goal of potable water supply, efforts are required to improve water supply, sanitation coverage and it is important to regularly assess the pollution risks to water sources posed by improper onsite sanitation systems. Based on the classification of irrigation water according to Water Salinity, Sodium adsorption ratio (SAR), Residual sodium carbonate (RSC), Permeability index and Magnesium ratio values, all the sample locations are suitable for irrigation purposes.