Undai River Diversion Project in Oyu Tolgoi

Undai river diversion project in Oyu Tolgoi Bazardorj, Sod-Erdene; Purevsuren, Uuganbayar Oyu Tolgoi is copper and gold mining project located in Gobi Desert region of southern Mongolia. The Oyu Tolgoi mine is situated in a desert-steppe ecosystem, where surface water, in the form of alluvial sub-surface flows and intermittent surface flows in dry river channels play an important role in supporting ecosystems and traditional herding practices. The Undai River (an ephemeral river) flows through the Oyu Tolgoi mine lease area and is close to the open pit. The development of the Oyu Tolgoi open pit and dewatering operations were going to affect Undai dry river bed, which required relocating a portion of the river channel mitigate effect to downstream water movement. Undai River diversion system was developed in 2012-2013 and consists of diversion dams, flood water diversion channel, and subsurface flow diversion. Thus subsurface and surface flows of Undai dry river bed were diverted from its original course, away from effect zone of the open pit, and rejoined the natural channel downstream of Mine Lease Area. Upon completion of construction works in 2013, long term comprehensive environment monitoring has been conducted. Monitoring has included water level (in monitoring wells and herder wells), water laboratory analysis, surface and subsurface flow rates, flood monitoring and observations. Water quality has improved at the New Bor ovoo spring fresh water and water quality now complies with the Mongolian potable water standard parameters. Measured flow rate range at the New Bor ovoo spring have been 0.3 – 2.6 L/s, depending on summer- autumn rain events. No adverse effect on herders’ shallow groundwater wells and local water courses downstream of the diversion structure have been identified in five years of monitoring. Heavy floods occurred in the summers 2017 and 2018 due to the heavy rainfall events. Surface flows successfully passed through the flood water diversion channel. The Undai River Diversion Project has been successfully constructed and tested through high rainfall years of 2017 and 2018. The diversion has enabled the development and operation of the open pit, while maintain water levels in shallow wells downstream of the Oyu Tolgoi. The monitoring has demonstrated no change natural regime of downstream alluvial water levels and an improvement in water quality. An unexpected benefit has been the wide range of wildlife species and domestic animals that utilize the New Bor ovoo spring.

Wolkersdorfer, Ch.; Khayrulina, E.; Polyakova, S.; Bogush, A. (Editors) 295 IMWA 2019 “Mine Water: Technological and Ecological Challenges”

Undai river diversion project in Oyu Tolgoi Environment department, Oyu Tolgoi LLC, Mongolia Sod-Erdene Bazardorj, Uuganbayar Purevsuren

Oyu Tolgoi mine site Environment monitoring

The Oyu Tolgoi copper-gold mine is located in the southeast region of Gobi Upon completion of construction works in 2013, long term comprehensive region of Mongolia, approximately 80 km north of China-Mongolian border. Oyu environment monitoring has been conducted. Monitoring has included water tolgoi is a remote project and extensive infrastructure has been constructed level (in monitoring wells and herder wells), water laboratory analysis, surface including: Water Supply Borefield, Tailings Storage Facility, Concentrator, Waste and subsurface flow rates, flood monitoring and observations. . Water Treatment Plant, Water Treatment & Bottling Plant, highways, housing, and Undai river diversion project.

It is situated in a desert-steppe ecosystem, where surface water, in the form of alluvial sub-surface flows and intermittent surface flows in dry river channels play an important role in supporting ecosystems and traditional herding practices.

Water quality has improved at the New Bor ovoo spring fresh water and water quality now complies with the Mongolian potable water standard parameters. Measured flow rate range at the New Bor ovoo spring have been 0.3 – 2.6 L/s, depending on summer-autumn rain events.

Water quality parameters of water point located in Undai river New Bor ovoo spring flow rate 1000 3 3.00 623 298.00 286.7 146.45

100 77.0 59.61 2.5 2.50 Introduction 88.3 55.74 43.8 40.84 72.9 42.54 V-notch

10 16.8 5.04 2 2.00

5.02 2.54 Undai dry riverbed is about 120 km long and has 1081 m2 basin area collecting 2.8 1.48 2.1 1 0.72 1.5 1.50

0.51 Flow L/sec rate,

clean subsurface water source for both local community and wildlife. The Undai (Log) Concentration 0.3 0.1 0.08 1 1.00 River (an ephemeral river) flows through the Oyu Tolgoi mine lease area and is 0.05 0.03

<0.01 close to the open pit. The development of the Oyu Tolgoi open pit and 0.01 0.5 A little 0.50 Frozen Frozen Frozen Frozen dewatering operations were going to affect Undai dry riverbed, which relocated Frozen water

0 0.00 a portion of the river channel to mitigate impacts to downstream water Old Bor-Ovoo spring New Bor-Ovoo spring MNS 900-2018. Potable water standard 2013 Sep 2014 Mar 2014 Sep 2015 Mar 2015 Sep 2016 Mar 2016 Sep 2017 Mar 2017 Sep 2018 Mar 2018 Sep movement. No adverse impact on herders’ shallow groundwater wells and local water courses downstream of the diversion structure have been identified in five years of monitoring.

New Bor Ovoo spring area variation

37787 36000

33003 32000

28000

24000 24363 ) 2     20000 19476 18515 Area ( 16000

12000

8000 7850

4000

0 2013 Sep 2014 Mar 2014 Sep 2015 Mar 2015 Sep 2016 Mar 2016 Sep 2017 Mar 2017 Sep 2018 Mar 2018 Sep

The Undai River Diversion Project has been successfully constructed and tested through high rainfall years of 2017 and 2018. The diversion has enabled the development and operation of the open pit, while maintain water levels in shallow wells downstream of the Oyu Tolgoi. The monitoring has demonstrated no change natural regime of downstream alluvial water levels and an improvement in water quality. An unexpected benefit has been the wide range of wildlife species and domestic animals that utilize the New Bor ovoo spring.

Undai River diversion system was finalized in 2013 and consists of diversion dams, flood water diversion channel, and subsurface flow diversion.

Thus subsurface and surface flows of Undai dry river bed were diverted from its original course, away from impact zone of the open pit, and rejoined the natural channel downstream of Mine Lease Area.

296 Wolkersdorfer, Ch.; Khayrulina, E.; Polyakova, S.; Bogush, A. (Editors)