Open access, Peer-reviewed and Indexed international journal (www.journalresearchijf.com) 30 Environmental contaminants and their impact on subsurface water by using Water Quality Index (WQI) method of different wells - A case study of Wama Hagelo District, Western Ethiopia. * Dr. Shayaq Ali 1 , Lalisa Asefa Mekonin 2 1 Professor, Department of Earth Sciences, Wollega University, P.O Box 395, Nekemte, ETHIOPIA 2 Researcher, Department of Earth Sciences, Wollega University, P.O Box 395, Nekemte, ETHIOPIA The Water Quality Index (WQI) in different wells in Wama Hagalo district, Oromia region, western part of Ethiopia, was calculated in order to ascertain the quality of water for public consumption.WQI indicates water quality in terms of index numbers and offers a useful representation of overall quality of water. In this study, WQI was determined on the basis of various physic-chemical parameters, Ph, hardness ,calcium,magnesium,sodium,chloride,nitrite,TDS,iron,manganese,and fluorides. This has been determined based on the physic-chemical water sample analyzed during past time when the well- developed measured at the water works design and supervision Enterprise laboratory of Addis Ababa. The WQI for these wells ranges from14.39 to 83.36. The high value of WQI has been found to be mainly from the higher values of iron, nitrite, total dissolved solids, hardness, fluorides and manganese in the subsurface water. The results of analyses have been used to suggest models for predicting water quality. The analysis reveals that the some subsurface water of the area needs some degree of treatment before consumption, and it also needs to be protected from the perils of contamination. The computed WQI for point W4indicates an excellent quality of water while the value of W5 (42.64) falls within (26-50) of the classification of water quality based on weighted arithmetic WQI method and falls in the rank of good quality. The three wells namely of: Ketare, Laga Dhoke and Kushi Dima have poor quality of subsurface water and hence needs treatment before consumption. The WQI for the well point W6, ranges between 76-100 and indicates very poor quality of water which needs especial treatment to use it for drinking purpose. We already concluded that the WQI method is a very effective tool for determining the quality of water susceptible to leachate pollution and communicating it in an unambiguous manner to the stakeholders in the water industry. Keywords : Parameters, Physico-chemical, Subsurface water, Water Quality Index, Weighted Arithmetic method. I. INTRODUCTION Water is one of the most important major natural resources of the ecosystem, necessary for human consumption, domestic services, agriculture, industry, manufacturing and other sectors. The quality of the subsurface water receivers is influenced by pollution of soil and air, industrial and domestic waste disposal, organic components, pathogenic microorganisms, application of fertilizers and pesticides in agriculture .The subsurface water quality is normally characterized by different physico-chemical characteristics. These parameters change widely due to the various types of pollution, seasonal fluctuation, subsurface water extraction, The nature of the rock formations, topography, soils, atmospheric precipitation, quality of the recharged water and subsurface geochemical process and affects subsurface water quality (Todd, 1980, Fetter, 1994). Hence a continuous monitoring on subsurface water becomes mandatory in order to minimize the subsurface water pollution and have control on the pollution-caused agents. Water quality index is one of the most effective tools to communicate information on the quality of water to the concerned citizens and policy makers. It, thus, becomes an important parameter for the assessment and management of subsurface water. WQI is defined as a rating reflecting the composite influence of different water quality parameters. The use of water quality index (WQI) in ADVANCE RESEARCH JOURNAL OF MULTIDISCIPLINARY DISCOVERIES ISSN : 2456-1045 VOL.39 I ISSUE-1 I CHAPTER-4 PUBLISHER : INTERNATIONAL JOURNAL FOUNDATION (IJF) ISSN : 2456-1045 (Online) (ICV-APS/Impact Value): 72.30 (GIF) Impact Factor: 5.188 Publishing Copyright @ International Journal Foundation Journal Code: ARJMD/APS/V-39.0/I-1/C-4/JULY-2019 Category : APPLIED SCIENCE Volume : 39.0/Chapter- IV/Issue -1 (JULY-2019) Journal Website: www.journalresearchijf.com Paper Received: 23.07.2019 Paper Accepted: 02.08.2019 Date of Publication: 10-08-2019 Page: 30-37 ORIGINAL RESEARCH ARTICLE Name of the Corresponding author: Shayaq Ali * Professor, Department of Earth Sciences, Wollega University, P.O Box 395, Nekemte, ETHIOPIA CITATION OF THE ARTICLE Ali S., Mekonin LA. (2019) Environmental contaminants and their impact on subsurface water by using Water Quality Index (WQI) method of different wells - A case study of Wama Hagelo District, Western Ethiopia.; Advance Research Journal of Multidisciplinary Discoveries;39(4)pp.30-37 ABSTRACT