Oyu Tolgoi Water Supply Project/ Galbyn and Gobi Gunii groundwater resource exploitation
IMMI is the owner and proponent of the development of the Oyu Tolgoi Project (the Project) which is located in the South Gobi region of Mongolia, approximately 570 km south of Ulaanbaatar and 80 km north of the Chinese-Mongolian border. IMMI is a wholly owned subsidiary of Ivanhoe Mines Ltd, a mining and exploration company listed in Canada and the United States.
The Oyu Tolgoi Project is proposed to use conventional crushing, grinding and flotation treatment processes to initially treat 70000 tonnes per day (tpd) of ore, increasing to 85000 tpd during the first five years of operation, for the production of a copper concentrate suitable for sale to smelters. The process requires sufficient water to meet peak demands and variations associated with process dynamics and the effect of extreme temperature variations.
The initial Project water supply requirement is expected to vary between 130 and 729 L/s (11 232 and 63 000 m3/day ) with an average operating demand of 430 L/s (37152 m3/day) for the 70 000 tpd production rate rising to an average of 518L/s (44 755 m3/day) for the 85 000 tpd rate .
The availability of a reliable and economically feasible water supply for the Oyu Tolgoi Project is critical to the success of the project. The project is located in an area with an average precipitation of approximately 80 mm per year. The surrounding desert and semi-desert steppe contains no significant surface water resources and no water supply infrastructure exists in the region apart from shallow hand dug wells and occasional deep water bores that supply traditional nomadic herders and communities.
IMMI has carried out water exploration for the Project since 2002. Geological and hydrogeological information has been collected and analyzed within a 100 to 200 km zone surrounding the Project. Prospective areas for water resources were selected for further investigation through geophysical survey and, on the basis of results; exploratory drilling of potential target aquifers was completed in the Galbyn Gobi, Gunii Hooloi and Nariin Zag area. The results from initial exploratory drilling identified the Galbyn Gobi and Gunii Hooloi areas as the most likely water resource and detailed hydrogeological surveys in these areas was completed during 2003 and 2004.
The hydrogeological characteristics of these aquifers are presented in: “Report of Groundwater Exploration for Oyu Tolgoi Mine Water Supply Carried out Within Galbyn Gobi and Gunii Hooloi Areas in 2003-2004 (Munkhbaatar et al, 2004)”. This hydrogeological report forms the technical basis for water resource availability within the two aquifers and was submitted to the Mongolian Ministry for Nature and Environment in December 2004, in accordance with the requirements of Article 21.2 of the Mongolian Law on Water. The main findings of the resource study are:
- The total reserve of Gunii Hooloi water resource area was estimated by hydrodynamic method as 812.5 L/s (70 200 m3/day) over 25 years of continuous use. The total inferred reserves of the Galbyn Gobi water resources area is estimated at 370 L/s (32000 m3/day) over 25 years of continuous use. The available water reserve is calculated over 25 years in accordance with Mongolian practice and aligns with the water use contract period prescribed in the Mongolian Law on Water.
- The water quality of Gunii Hooloi regional aquifer can be used for industrial use but not for human consumption due to concentrations of dissolved salts up to 2.8 g/L. Galbyn Gobi groundwater quality varies with geological formations from 0.9 g/L in the unconfined aquifer to more than 8 g/L in the confined aquifer.
In undertaking EIA of the abstraction of project water supply from the identified groundwater resource, detailed surveys have been completed on the existing environmental condition and the inter-relationships between environmental components of these areas. Potential negative environmental, including socioeconomic, impacts of water abstraction over a 40 year mine life have been identified and assessed. Measures to prevent, minimize and mitigate identified negative impacts are recommended and environmental management and monitoring plans developed. All results of surveys and discussion of impacts and intended control measures are included in this report.
The objective of EIA is to determine all potential impacts during the period of groundwater abstraction with particular emphasis on soil moisture, groundwater, vegetation, fauna and local community and herder water supply. To satisfy this goal, Eco Trade LLC Environmental Consultants completed specific surveys, including:
- Environmental baseline studies in the territory of Galbyn Gobi and Gunii Hooloi water resource exploration areas during September and October, 2003, and from March to May 2004. Baseline studies included geological characteristics, hydrogeology, hydrological condition, soil cover, vegetation cover, fauna and local communities and their domestic livestock within the aquifer areas.
- Detailed surveys on the relationship between deep rooted vegetation and shallow water including: Siberian elm; saxaul; tamarisk, and Asiatic poplar trees which occur over the shallow aquifers and drainage systems within and surrounding the aquifer areas. The vegetation communities that occur over the aquifer areas were also studied to identify soil moisture dependence, drought tolerance and dormancy.
- Survey of water sources for local communities and herder families in and surrounding the water resource area including wells and surface water use by domestic livestock.
- A study of predicted hydrogeological impacts, groundwater drawdown, of long term abstraction from deep regional aquifers of Gunii Hooloi and Galbyn Gobi on the regional hydrogeology with specific attention to shallow groundwater resource impacts .
The main EIA study findings include:
- The Gunii Hooloi area has far less groundwater-dependent vegetation communities than the Galbyn Gobi and no direct connection between the deep and shallow aquifer. The saxaul plants (Haloxylon ammodendron) in Gunii Hooloiare not considered at threat from regional aquifer drawdown as they are shallow- rooted and access near-surface soil moisture. The Galbyn Gobi saxaul groves are substantially different in form and habit and access the water table beneath the terminal drainage basins.
- The Galbyn Gobi investigations have found some evidence of connection between the near-surface aquifer and the deeper regional aquifer. The potential for shallow-water depletion resulting from long-term drawdown of the Galbyn Gobi regional aquifer poses a risk to deep-rooted perennial vegetation within the low-lying terminal drainage basins of the Galbyn Gobi.
- Judging from the location of the wells and water supply for herder families within ground water resource areas, there are 41 wells within the Galbyn Gobi ground water resource area (17 of them in the drawdown area), and 72 wells within Gunii Hooloi ground water resource area (6 of them in the drawdown area). The results of detailed surveys on drawdown risk of shallow herder wells shows that shallow wells within the near surface aquifer are at low risk, especially in the Gunii Hooloi area. However, if long-term monitoring of the wells indicates an impact from the Project water supply, then IMMI has committed to providing alternative water supplies to affected herders.
The findings of the EIA, including an assessment of risk associated with long-term drawdown of the regional aquifer, indicates that the Gunii Hooloi ground water resource area can be used as the main resource for the project to supply an average ranging from 430 to 518 L/s ( 37 152 to 44 755 m3/day) . The use of the Gunii Hooloi aquifer for all the expected Project water requirements may result in an estimated maximum drawdown of the regional aquifer of up to 75 m over the expected mine life (Aquaterra, 2004) without undue risk to environmental and socio-economic values of the region
The potential for groundwater drawdown of the shallow water resources in the Galbyn Gobi requires that the development of this aquifer should be limited to the central aquifer area and drawdown of the regional aquifer limited to no more than 10m. The available water supply from the Galbyn Gobi has been modeled, with consideration of the limitations, and found to be capable of providing an additional 130 L/s (11 232 m3/day ) should this resource be required (Aquaterra, 2004)
The aquifer characteristics will be further defined during the first two years of borefield use as the long-term monitoring of shallow systems and drawdown responses will provide essential data for accurately defining the resource characteristics. It is recommended that a review of predicted drawdown and proposed borefield abstraction plans be undertaken following the first two years of operation. This review should include a review of the potential environmental impacts based on the revised drawdown predictions.
The initial period of operation will also provide information on the vegetation characteristics of the identified groundwater-dependent species and communities. Long-term monitoring of plant physiology is required over the initial two year period to obtain a greater understanding of the risk to vegetation species from changes to soil moisture availability and lowering of water levels. This research will be undertaken by a team which includes plant physiologists, botanists, soil scientists and hydro geologists in consultation with the Mongolian water resource agencies and relevant academic institutions.
The monitoring of groundwater, vegetation, fauna, herder wells and surface water features within the groundwater resource areas over the operational life of the borefield will be undertaken in accordance with the Environmental Monitoring Plan. The results from the monitoring program will be made available to relevant authorities, community leaders and existing groundwater users within the resource area. If the monitoring program indicates negative impacts from aquifer abstraction, the appropriate response to prevent or mitigate impacts will be developed in consultation with the relevant authorities and community representatives.
