[A-HW23] Hydrology & Water Environment

[AHW23-04] The spatial and temporal observation of heavy metals in groundwater around the Erdenet city, Mongolia

*Enkhuur Munkhsuld^1,3,4, Fukushi Keisuke², Murayama Takehiko¹, Altansukh Ochir^3,4, Nishikizawa Shigeo¹, Baasansuren Gankhurel², Solongo Tsetsgee^3,4, Ariuntungalag Yunden³, Tserenkhand Batbold³ (1.Department of Transdisciplinary Science and Engineering, School of Environment and Society, Tokyo Institute of Technology, Kanagawa 2268502, Japan, 2.Division of Natural System, Graduate School of Natural Science and Technology, Kanazawa University, Kanazawa 9201192, Japan, 3.Department of Environment and Forest Engineering, School of Engineering and Applied Sciences, National University of Mongolia, Ulaanbaatar 14200, Mongolia, 4.Institute for Sustainable Development, National University of Mongolia, Ulaanbaatar 14192, Mongolia)

Keywords:groundwater, heavy metals, Erdenet, spatial observation, temporal observation

While groundwater is a significant and valuable drinking water resource, it is vulnerable to different kinds of pollution including heavy metals, organic compounds, and many others and one of the common objects that have an impact on groundwater is mining. 99% of drinking water resources is groundwater in Mongolia represents research on groundwater is high importance. The research area, Erdenet city (49°01'40"N, 104°02'40"E) is known for Erdenet mine (Erdenet Mining Corporation), has been in operation since 1978, is considered one of the biggest copper-molybdenum mines in Mongolia and Asia. The Erdenet mine locates the south-eastern side of the city and transfers its wastewater to a tailing pond that locates the north-eastern side of the city. The wastewater in the tailing pond discharges into the river named Khangal flows out from the city. A total of 49 sampling points were chosen, including public and private wells, a natural spring and a tailing pond discharge. Trace metals and major metals, 27 metals were measured by ICP-OES and ICP-MS. Ga, Se, Bi were not observed at any sampling point. As a result of comparison with corresponding water quality permissible level by Mongolian National Standard (MNS) and World Health Organization (WHO), Mo and Ca concentrations were higher in several points. Mo concentration ranges between 1.04 - 1102.74 µg/l, and Ca concentration ranges between 36.63 – 277.24 mg/l. The most concerning result is that the tailing pond water contains high Mo with the highest concentration 1102.74 µg/l, and it exceeds the MNS 6148:2010 - “Water quality. Maximum limit of substance contaminating groundwater” by approximately 16 times higher. A natural spring locates 300 m away from tailing pond discharge contains 1064.02 µg/l Mo, which is high and similar with tailing pond discharge. Ca concentration was higher than the permissible level of the abovementioned standard at 21 points out of 49 points. The highest exceeded amount is 3 times higher than the permissible level. About the distribution of Ca, it is similar, the highest Ca concentrations were observed in a natural spring and a tailing pond discharge. Natural spring water contains a high concentration of Mo and Ca as mining tailing pond water. It makes the hypothesis that the wastewater is not purified effectively, and the wastewater in the tailing pond may affect groundwater.