Drinking water quality research of the soum centers and settled areas in south Gobi of Mongolia

Groundwater is vital resource for both the local people and livestock of the Gobi region of Southern Mongolia where surface water distribution is limited. Apparently, whether the water is suitable for drinking purpose is significant issue to study. The purpose of this study is to assess the quality of water in local water supply wells and to identify  hydrochemical facies and origin of the micro elements of the water. In the study, totally 233 water samples were collected from the existing water wells located in 77 soum centers and settled areas of 10 provinces of southern Mongolia. The water samples were analyzed at the Central Geological Laboratory in Ulaanbaatar. Major cations (K+, Na+, Ca2+, Mg2+, SiO2) and anions (Cl-, HCO3-, SO4-, NO2-, NO3-, F-) were determined. In addition, total 12 trace metals (Be, B, Cr, Mn, Cu, As, Se, Sr, Mo, Cd, Ba, U) have been determined by the ICP-124. As a result, the groundwater of the target region is identified to be alkaline and as for the mineralization, it refers to fresh or brakishwater type. Hydrochemical facies are identified to be the types of Ca-HCO3, NaCl, Ca-Na-HCO3 and Ca-Mg-Cl. Moreover, the sources of major ions of the groundwater in the region is characterized by more dominance of water and rock unit interaction and less impact of recharge and evaporation. When compared to drinking water standard, the hardness, Na ion and Mg ion exceed the maximum allowable limits in the water samples taken from water wells of 28 soums, 24 soums and 47 soums, respectively. The concentration of arsenic was higher than drinking water standards of World Health Organization (WHO) in 21 soums of the study area and other metals including uranium, strontium and selenium in water exceeded drinking water standards in 9 soums centers water supply wells.