Case study 2 - Managing intercepted groundwater by mining as a product in the Pilbara
Background and geographic area
There are multiple localised pockets of fresh water that have accumulated in the fractured rocks of the Pilbara region in Western Australia. The region is mineral rich: it has immense reserves of iron ore, many of which lie below the groundwater table. To enable access to the ore deposits, large volumes of water, often of excellent quality, must be moved. As the majority of mine sites have significant excess water there is a limited market, and as the sites are generally remote, the cost of transporting it to areas of demand is prohibitive at present.
Management aims to minimise risks to the environment and other users and to support a culture of effective water management within the industry, regardless of location. Management is effected though a water licence, which is the regulatory instrument that entitles the holder to take the water subject to conditions.
Application of a risk–based approach
Excess water at remote locations is managed against a hierarchy of objectives. The priority is to maintain groundwater dependent ecosystems that are affected by the drawdown or release of groundwater. For example, water is piped to mimic natural springs, and excess water is released downstream of the groundwater dependent system to prevent inundation.
Excess water is used onsite as far as possible, though consumptive use is generally only a small proportion of the total volume. Water is used to manage dust, and importantly, to limit dust from ore transport. This also includes conditioning of the ore to prevent dust during delivery to port operations. Often water efficiency isn't a key goal at these sites, as onsite use of water can offset the potential impacts of disposing of excess water.
Where feasible, once onsite needs are met, water is transported to nearby mining camps, towns or neighbouring water-short mines and used to supplement supplies.
Should there be no consumptive use options, then the possibility of injection back into the aquifer at designated sites must be assessed. If this is not an option, then controlled release to the environment is assessed.
In an environment of long, hot, dry periods punctuated by extreme floods, sustained inundation caused by release of excess water does cause localised changes. Initially, riparian vegetation flourishes along the drainage line from the point of release to where water dissipates into alluvial deposits along the creek bed. After several years of inundation, tree deaths can occur in this zone of inundation. Where there are no other viable options and long-term harm is localised and not greater than the natural variation, managed surface discharge is considered acceptable.
This water management approach seeks to align with other government project approvals to ensure a consistent approach to managing excess water from mining operations that operate below the groundwater table. In less remote sites, initiatives to enhance the economic potential of this water are currently being explored.
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