By Dennis Gibson, Sergio González, Raymond Philippe and Corné Pretorius
Designing well-integrated and holistic water management infrastructure for mining operations is a complex undertaking. The overarching infrastructure needs to integrate each individual system that supplies water to the mine – including those systems that transfer water within the mine site, and those that recycle, reuse and discharge effluent into the environment.
When developing a water balance model, miners should consider all key input and output supply, use and discharge. The model needs to be based on a thorough understanding of the water infrastructure, pipelines and pumping stations, including storage systems, water treatment systems, infiltration systems, and diversion channels. External variables such as hydrology, hydrogeology, climate change and environmental regulations will also be influencer, along with social requirements and regulatory considerations.
In order to deliver accurate outcomes at any given time, miners should regularly review their water balance and identify any changes in supply, storage and demand. This means addressing supply, treatment and effluent discharge from the perspective of the overall operational mineral processing capacity. Understanding the mine’s time-dependent water requirements will offer two primary benefits by helping to lower the risk of production losses and reducing the risk of increased water management costs.
A well-designed water balance model will ensure that miners lower the risk of incorrect sizing of water management infrastructure, be it over or under sizing. For example, if a mine overestimates its water needs, it could result in overly inflated infrastructure, with higher capital expenditure and increased operating and maintenance costs. But if a mine underestimates demand, it could end up with undersized infrastructure, which would result in insufficient supply and inadequate treatment.
Designing for Various Water Situations
In order to design an appropriate integrated water infrastructure plan, miners need to gain a thorough understanding of the seasonal availability of both surface and underground water, and the levels of flow rates at the mine site. Mine operators typically encounter three different water environments when designing for specific mining locations: an ongoing excess of water; continuous regional water shortages; and a mixed-variable situation, where mine operators deal with both wet and dry seasons.
In excess water situations, most commonly found in tropical regions, the challenge comes down to managing discharge to minimize potential environmental impact. This includes optimizing effluent treatment capacity and peak flow management and storage.
In the past, several mines have had to deal with the repercussions of mismanaging discharge. This has caused significant reputational damage and has even led to production stoppages and a loss of license to operate. To help minimize the risk of potential contact water generation, the mine should incorporate diversion infrastructure designed to help keep clean water clean. Stormwater also needs to be managed, both to protect the mine water infrastructure and the environment.
Designing for water shortages is common in regions such as northern Chile, southern Peru, South Africa and Australia, and other arid regions. When designing mines in these areas, operators need to implement water-efficient conservation design strategies and prioritize the need for an adequate storage system that can supply water as needed. To appropriately size the infrastructure, miners should look to comprehensive water make-up requirements including evaporation, infiltration, processing, tailings and other losses, while the storage systems should be designed to compensate for changes in the water balance. Taking this approach helps mitigate risk in two ways – by tightening investment and capital expenditure, and by managing production losses.
The most common scenario is the mixed-variable scenario, where miners need to deal with both water excess and shortage. These situations may be the most complex, as mine operators need to prepare for both floods and droughts. The primary challenge comes down to balancing the risk of insufficient supply during dry periods with risks resulting from contamination during wet periods and floods.
This where a well-designed, robust dynamic water balance model is invaluable. Using this model, miners can explore various extreme scenarios by producing statistical functions that quantify the probability of these outcomes. This type of modelling enables the designer to plan a system that is not only optimally sized, but suitably priced and with sufficient protective measures in place. The water balance model also allows the mine’s water management team to monitor forecasts and identify trends, while offering the option to re-calibrate the model as needed to help mitigate risk and optimize mine production.