Journal of Water Resource and Protection, 2011, 3, 398-414 doi:10.4236/jwarp.2011.36050 Published Online June 2011 (http://www.SciRP.org/journal/jwarp) Copyright © 2011 SciRes. JWARP Application of Index Analysis to Evaluate the Water Quality of the Tuul River in Mongolia Ochir Altansukh 1* , G. Davaa 2 1 Department of Geo-ecology and Environmental Study, School of Earth Sciences, National University of Mongolia, Ulaanbaatar, Mongolia 2 Water Research Sector, Institute of Meteorology and Hydrology, Mongolia E-mail: altansukh@num.edu.mn Received April 9, 2011; revised May 11, 2011; accepted June 11, 2011 Abstract A study of water pollution determinands of the Tuul River was carried out in surrounding area of Ulaan- baatar, the capital of Mongolia at 14 monitoring sites, using an extensive dataset between 1998 and 2008. An index method, developed by Ministry of Nature and Environment of Mongolia, applied for assessment and total, seven hydro-chemicals used in the index calculation. The research indicates that the Tuul River is not polluted until the Ulaanbaatar city and the contamination level spike appears when the river entering the city. The upper reaches of the river and tributaries have relatively good quality waters. Several pollution sources exist in the study area. Among them, the Central Wastewater Treatment Plant (CWTP) is a strongest point source in the downstream section of the river, recently. Pollutions at sites 7 - 10 are strongly dependant ef- fluent treatment levels from the plant, and it contains a high amount of chemicals that can cause of major decrement of the water quality. This would definitely kill aquatic fauna in the stretch of the river affected. It certainly happened in 2007. The general trend of water quality gradually has been decreased in the study pe- riod. Clearly, there is a need to improve the water quality in the Tuul River in surrounding area of the Ulaanbaatar. In order to change this situation, operation enhancement of treatment plants, a water quality modeling and artificial increment of dissolved oxygen concentrations become crucial to improve the water quality significantly. Perhaps a new wastewater treatment plant is needed for Ulaanbaatar city. Keywords: Tuul River, Water Quality Assessment, Pollution Point Source, Water Quality Map, Water Quality Index 1. Introduction Unpolluted waters in rivers are a vital natural resource, providing drinking and irrigation water for humans, live- stock and agriculture. However, water quality in many large river waters has deteriorated significantly world wide due to anthropogenic activities in the past two-three decades [1]. It is also widely accepted that discharges from sewage treatment plants provide major fluxes of P and N to rivers, predominantly in populated urban areas [2,3]. Nutrient enrichment can result in excessive growth of aquatic plants and reductions in dissolved oxygen [4,5]. Rising pollution levels and the increasing demand for water and the associated increased discharges of pollut- ants are having significant impacts on the water cycle and water quality [6,7]. Climate change is also starting to have some effects with increasing temperatures and changed rainfall patterns. The increasing air temperatures and decreasing river flows in warmer months are the main concerns, and intensive water use is often con- strained by the lack of natural low flow, and low flow rivers are more affected by effluent discharges from cit- ies, industries, and agriculture [8,9]. Surface waters in Mongolia have tended to decrease in recent years due to the combined effect caused by the decrease of precipita- tion and the increase of potential evaporation as a result of rising air temperature. This situation indicates that droughts may occur more frequently due to the effects of global warming [10]. The use of water quality index (WQI) simplifies the presentation of results of an investigation related to a water body as it summarises in one value or concept a series of parameters analysed. In this way, the indices are